diff --git a/upstream_utils/fmt.py b/upstream_utils/fmt.py
index daad0523fd..13684622a7 100755
--- a/upstream_utils/fmt.py
+++ b/upstream_utils/fmt.py
@@ -34,7 +34,8 @@ def copy_upstream_src(wpilib_root: Path):
 def main():
     name = "fmt"
     url = "https://github.com/fmtlib/fmt"
-    tag = "11.1.4"
+    # master on 2025-07-06
+    tag = "300ce75ca610cc33cf51366572261bb974aada7b"
 
     fmt = Lib(name, url, tag, copy_upstream_src)
     fmt.main()
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/args.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/args.h
index 3ff4788074..d8fe241c73 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/args.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/args.h
@@ -71,7 +71,7 @@ class dynamic_arg_list {
  * It can be implicitly converted into `fmt::basic_format_args` for passing
  * into type-erased formatting functions such as `fmt::vformat`.
  */
-template <typename Context> class dynamic_format_arg_store {
+FMT_EXPORT template <typename Context> class dynamic_format_arg_store {
  private:
   using char_type = typename Context::char_type;
 
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/base.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/base.h
index b886317d6a..81d8fc0369 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/base.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/base.h
@@ -21,7 +21,7 @@
 #endif
 
 // The fmt library version in the form major * 10000 + minor * 100 + patch.
-#define FMT_VERSION 110104
+#define FMT_VERSION 110201
 
 // Detect compiler versions.
 #if defined(__clang__) && !defined(__ibmxl__)
@@ -209,20 +209,6 @@
 #  define FMT_DEPRECATED /* deprecated */
 #endif
 
-#ifdef FMT_ALWAYS_INLINE
-// Use the provided definition.
-#elif FMT_GCC_VERSION || FMT_CLANG_VERSION
-#  define FMT_ALWAYS_INLINE inline __attribute__((always_inline))
-#else
-#  define FMT_ALWAYS_INLINE inline
-#endif
-// A version of FMT_ALWAYS_INLINE to prevent code bloat in debug mode.
-#ifdef NDEBUG
-#  define FMT_INLINE FMT_ALWAYS_INLINE
-#else
-#  define FMT_INLINE inline
-#endif
-
 #if FMT_GCC_VERSION || FMT_CLANG_VERSION
 #  define FMT_VISIBILITY(value) __attribute__((visibility(value)))
 #else
@@ -249,6 +235,28 @@
 #  define FMT_MSC_WARNING(...)
 #endif
 
+// Enable minimal optimizations for more compact code in debug mode.
+FMT_PRAGMA_GCC(push_options)
+#if !defined(__OPTIMIZE__) && !defined(__CUDACC__) && !defined(FMT_MODULE)
+FMT_PRAGMA_GCC(optimize("Og"))
+#  define FMT_GCC_OPTIMIZED
+#endif
+FMT_PRAGMA_CLANG(diagnostic push)
+
+#ifdef FMT_ALWAYS_INLINE
+// Use the provided definition.
+#elif FMT_GCC_VERSION || FMT_CLANG_VERSION
+#  define FMT_ALWAYS_INLINE inline __attribute__((always_inline))
+#else
+#  define FMT_ALWAYS_INLINE inline
+#endif
+// A version of FMT_ALWAYS_INLINE to prevent code bloat in debug mode.
+#if defined(NDEBUG) || defined(FMT_GCC_OPTIMIZED)
+#  define FMT_INLINE FMT_ALWAYS_INLINE
+#else
+#  define FMT_INLINE inline
+#endif
+
 #ifndef FMT_BEGIN_NAMESPACE
 #  define FMT_BEGIN_NAMESPACE \
     namespace fmt {           \
@@ -297,13 +305,6 @@
   using unused = int[];          \
   (void)unused { 0, (expr, 0)... }
 
-// Enable minimal optimizations for more compact code in debug mode.
-FMT_PRAGMA_GCC(push_options)
-#if !defined(__OPTIMIZE__) && !defined(__CUDACC__) && !defined(FMT_MODULE)
-FMT_PRAGMA_GCC(optimize("Og"))
-#endif
-FMT_PRAGMA_CLANG(diagnostic push)
-
 FMT_BEGIN_NAMESPACE
 
 // Implementations of enable_if_t and other metafunctions for older systems.
@@ -325,8 +326,8 @@ using underlying_t = typename std::underlying_type<T>::type;
 template <typename T> using decay_t = typename std::decay<T>::type;
 using nullptr_t = decltype(nullptr);
 
-#if FMT_GCC_VERSION && FMT_GCC_VERSION < 500
-// A workaround for gcc 4.9 to make void_t work in a SFINAE context.
+#if (FMT_GCC_VERSION && FMT_GCC_VERSION < 500) || FMT_MSC_VERSION
+// A workaround for gcc 4.9 & MSVC v141 to make void_t work in a SFINAE context.
 template <typename...> struct void_t_impl {
   using type = void;
 };
@@ -466,8 +467,7 @@ template <typename T> constexpr const char* narrow(const T*) { return nullptr; }
 constexpr FMT_ALWAYS_INLINE const char* narrow(const char* s) { return s; }
 
 template <typename Char>
-FMT_CONSTEXPR auto compare(const Char* s1, const Char* s2, std::size_t n)
-    -> int {
+FMT_CONSTEXPR auto compare(const Char* s1, const Char* s2, size_t n) -> int {
   if (!is_constant_evaluated() && sizeof(Char) == 1) return memcmp(s1, s2, n);
   for (; n != 0; ++s1, ++s2, --n) {
     if (*s1 < *s2) return -1;
@@ -526,20 +526,20 @@ template <typename Char> class basic_string_view {
 
   constexpr basic_string_view() noexcept : data_(nullptr), size_(0) {}
 
-  /// Constructs a string reference object from a C string and a size.
+  /// Constructs a string view object from a C string and a size.
   constexpr basic_string_view(const Char* s, size_t count) noexcept
       : data_(s), size_(count) {}
 
   constexpr basic_string_view(nullptr_t) = delete;
 
-  /// Constructs a string reference object from a C string.
+  /// Constructs a string view object from a C string.
 #if FMT_GCC_VERSION
   FMT_ALWAYS_INLINE
 #endif
   FMT_CONSTEXPR20 basic_string_view(const Char* s) : data_(s) {
 #if FMT_HAS_BUILTIN(__builtin_strlen) || FMT_GCC_VERSION || FMT_CLANG_VERSION
-    if (std::is_same<Char, char>::value) {
-      size_ = __builtin_strlen(detail::narrow(s));
+    if (std::is_same<Char, char>::value && !detail::is_constant_evaluated()) {
+      size_ = __builtin_strlen(detail::narrow(s));  // strlen is not constexpr.
       return;
     }
 #endif
@@ -548,7 +548,7 @@ template <typename Char> class basic_string_view {
     size_ = len;
   }
 
-  /// Constructs a string reference from a `std::basic_string` or a
+  /// Constructs a string view from a `std::basic_string` or a
   /// `std::basic_string_view` object.
   template <typename S,
             FMT_ENABLE_IF(detail::is_std_string_like<S>::value&& std::is_same<
@@ -585,7 +585,6 @@ template <typename Char> class basic_string_view {
     return starts_with(basic_string_view<Char>(s));
   }
 
-  // Lexicographically compare this string reference to other.
   FMT_CONSTEXPR auto compare(basic_string_view other) const -> int {
     int result =
         detail::compare(data_, other.data_, min_of(size_, other.size_));
@@ -616,7 +615,7 @@ template <typename Char> class basic_string_view {
 
 using string_view = basic_string_view<char>;
 
-/// Specifies if `T` is an extended character type. Can be specialized by users.
+// DEPRECATED! Will be merged with is_char and moved to detail.
 template <typename T> struct is_xchar : std::false_type {};
 template <> struct is_xchar<wchar_t> : std::true_type {};
 template <> struct is_xchar<char16_t> : std::true_type {};
@@ -625,7 +624,7 @@ template <> struct is_xchar<char32_t> : std::true_type {};
 template <> struct is_xchar<char8_t> : std::true_type {};
 #endif
 
-// DEPRECATED! Will be replaced with an alias to prevent specializations.
+// Specifies if `T` is a character (code unit) type.
 template <typename T> struct is_char : is_xchar<T> {};
 template <> struct is_char<char> : std::true_type {};
 
@@ -1032,6 +1031,11 @@ enum {
 
 struct view {};
 
+template <typename T, typename Enable = std::true_type>
+struct is_view : std::false_type {};
+template <typename T>
+struct is_view<T, bool_constant<sizeof(T) != 0>> : std::is_base_of<view, T> {};
+
 template <typename Char, typename T> struct named_arg;
 template <typename T> struct is_named_arg : std::false_type {};
 template <typename T> struct is_static_named_arg : std::false_type {};
@@ -1064,6 +1068,16 @@ template <typename Char> struct named_arg_info {
   int id;
 };
 
+// named_args is non-const to suppress a bogus -Wmaybe-uninitialized in gcc 13.
+template <typename Char>
+FMT_CONSTEXPR void check_for_duplicate(named_arg_info<Char>* named_args,
+                                       int named_arg_index,
+                                       basic_string_view<Char> arg_name) {
+  for (int i = 0; i < named_arg_index; ++i) {
+    if (named_args[i].name == arg_name) report_error("duplicate named arg");
+  }
+}
+
 template <typename Char, typename T, FMT_ENABLE_IF(!is_named_arg<T>::value)>
 void init_named_arg(named_arg_info<Char>*, int& arg_index, int&, const T&) {
   ++arg_index;
@@ -1071,6 +1085,7 @@ void init_named_arg(named_arg_info<Char>*, int& arg_index, int&, const T&) {
 template <typename Char, typename T, FMT_ENABLE_IF(is_named_arg<T>::value)>
 void init_named_arg(named_arg_info<Char>* named_args, int& arg_index,
                     int& named_arg_index, const T& arg) {
+  check_for_duplicate<Char>(named_args, named_arg_index, arg.name);
   named_args[named_arg_index++] = {arg.name, arg_index++};
 }
 
@@ -1084,12 +1099,13 @@ template <typename T, typename Char,
           FMT_ENABLE_IF(is_static_named_arg<T>::value)>
 FMT_CONSTEXPR void init_static_named_arg(named_arg_info<Char>* named_args,
                                          int& arg_index, int& named_arg_index) {
+  check_for_duplicate<Char>(named_args, named_arg_index, T::name);
   named_args[named_arg_index++] = {T::name, arg_index++};
 }
 
 // To minimize the number of types we need to deal with, long is translated
 // either to int or to long long depending on its size.
-enum { long_short = sizeof(long) == sizeof(int) };
+enum { long_short = sizeof(long) == sizeof(int) && FMT_BUILTIN_TYPES };
 using long_type = conditional_t<long_short, int, long long>;
 using ulong_type = conditional_t<long_short, unsigned, unsigned long long>;
 
@@ -1662,12 +1678,12 @@ template <typename... T> struct arg_pack {};
 template <typename Char, int NUM_ARGS, int NUM_NAMED_ARGS, bool DYNAMIC_NAMES>
 class format_string_checker {
  private:
-  type types_[max_of(1, NUM_ARGS)];
-  named_arg_info<Char> named_args_[max_of(1, NUM_NAMED_ARGS)];
+  type types_[max_of<size_t>(1, NUM_ARGS)];
+  named_arg_info<Char> named_args_[max_of<size_t>(1, NUM_NAMED_ARGS)];
   compile_parse_context<Char> context_;
 
   using parse_func = auto (*)(parse_context<Char>&) -> const Char*;
-  parse_func parse_funcs_[max_of(1, NUM_ARGS)];
+  parse_func parse_funcs_[max_of<size_t>(1, NUM_ARGS)];
 
  public:
   template <typename... T>
@@ -1706,7 +1722,17 @@ class format_string_checker {
       -> const Char* {
     context_.advance_to(begin);
     if (id >= 0 && id < NUM_ARGS) return parse_funcs_[id](context_);
-    while (begin != end && *begin != '}') ++begin;
+
+    // If id is out of range, it means we do not know the type and cannot parse
+    // the format at compile time. Instead, skip over content until we finish
+    // the format spec, accounting for any nested replacements.
+    for (int bracket_count = 0;
+         begin != end && (bracket_count > 0 || *begin != '}'); ++begin) {
+      if (*begin == '{')
+        ++bracket_count;
+      else if (*begin == '}')
+        --bracket_count;
+    }
     return begin;
   }
 
@@ -2006,6 +2032,17 @@ struct has_back_insert_iterator_container_append<
                         .append(std::declval<InputIt>(),
                                 std::declval<InputIt>()))>> : std::true_type {};
 
+template <typename OutputIt, typename InputIt, typename = void>
+struct has_back_insert_iterator_container_insert_at_end : std::false_type {};
+
+template <typename OutputIt, typename InputIt>
+struct has_back_insert_iterator_container_insert_at_end<
+    OutputIt, InputIt,
+    void_t<decltype(get_container(std::declval<OutputIt>())
+                        .insert(get_container(std::declval<OutputIt>()).end(),
+                                std::declval<InputIt>(),
+                                std::declval<InputIt>()))>> : std::true_type {};
+
 // An optimized version of std::copy with the output value type (T).
 template <typename T, typename InputIt, typename OutputIt,
           FMT_ENABLE_IF(is_back_insert_iterator<OutputIt>::value&&
@@ -2020,6 +2057,8 @@ FMT_CONSTEXPR20 auto copy(InputIt begin, InputIt end, OutputIt out)
 template <typename T, typename InputIt, typename OutputIt,
           FMT_ENABLE_IF(is_back_insert_iterator<OutputIt>::value &&
                         !has_back_insert_iterator_container_append<
+                            OutputIt, InputIt>::value &&
+                        has_back_insert_iterator_container_insert_at_end<
                             OutputIt, InputIt>::value)>
 FMT_CONSTEXPR20 auto copy(InputIt begin, InputIt end, OutputIt out)
     -> OutputIt {
@@ -2029,7 +2068,11 @@ FMT_CONSTEXPR20 auto copy(InputIt begin, InputIt end, OutputIt out)
 }
 
 template <typename T, typename InputIt, typename OutputIt,
-          FMT_ENABLE_IF(!is_back_insert_iterator<OutputIt>::value)>
+          FMT_ENABLE_IF(!(is_back_insert_iterator<OutputIt>::value &&
+                          (has_back_insert_iterator_container_append<
+                               OutputIt, InputIt>::value ||
+                           has_back_insert_iterator_container_insert_at_end<
+                               OutputIt, InputIt>::value)))>
 FMT_CONSTEXPR auto copy(InputIt begin, InputIt end, OutputIt out) -> OutputIt {
   while (begin != end) *out++ = static_cast<T>(*begin++);
   return out;
@@ -2236,6 +2279,7 @@ template <typename Context> class value {
   }
 
   // Formats an argument of a custom type, such as a user-defined class.
+  // DEPRECATED! Formatter template parameter will be removed.
   template <typename T, typename Formatter>
   static void format_custom(void* arg, parse_context<char_type>& parse_ctx,
                             Context& ctx) {
@@ -2311,8 +2355,9 @@ template <typename Context, int NUM_ARGS, int NUM_NAMED_ARGS,
           unsigned long long DESC>
 struct named_arg_store {
   // args_[0].named_args points to named_args to avoid bloating format_args.
-  arg_t<Context, NUM_ARGS> args[1 + NUM_ARGS];
-  named_arg_info<typename Context::char_type> named_args[NUM_NAMED_ARGS];
+  arg_t<Context, NUM_ARGS> args[1u + NUM_ARGS];
+  named_arg_info<typename Context::char_type>
+      named_args[static_cast<size_t>(NUM_NAMED_ARGS)];
 
   template <typename... T>
   FMT_CONSTEXPR FMT_ALWAYS_INLINE named_arg_store(T&... values)
@@ -2345,7 +2390,7 @@ struct format_arg_store {
   // +1 to workaround a bug in gcc 7.5 that causes duplicated-branches warning.
   using type =
       conditional_t<NUM_NAMED_ARGS == 0,
-                    arg_t<Context, NUM_ARGS>[max_of(1, NUM_ARGS)],
+                    arg_t<Context, NUM_ARGS>[max_of<size_t>(1, NUM_ARGS)],
                     named_arg_store<Context, NUM_ARGS, NUM_NAMED_ARGS, DESC>>;
   type args;
 };
@@ -2703,7 +2748,7 @@ template <typename... T> struct fstring {
   template <size_t N>
   FMT_CONSTEVAL FMT_ALWAYS_INLINE fstring(const char (&s)[N]) : str(s, N - 1) {
     using namespace detail;
-    static_assert(count<(std::is_base_of<view, remove_reference_t<T>>::value &&
+    static_assert(count<(is_view<remove_cvref_t<T>>::value &&
                          std::is_reference<T>::value)...>() == 0,
                   "passing views as lvalues is disallowed");
     if (FMT_USE_CONSTEVAL) parse_format_string<char>(s, checker(s, arg_pack()));
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/chrono.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/chrono.h
index 50c777c841..6f9a363efd 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/chrono.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/chrono.h
@@ -22,21 +22,6 @@
 
 #include "format.h"
 
-namespace fmt_detail {
-struct time_zone {
-  template <typename Duration, typename T>
-  auto to_sys(T)
-      -> std::chrono::time_point<std::chrono::system_clock, Duration> {
-    return {};
-  }
-};
-template <typename... T> inline auto current_zone(T...) -> time_zone* {
-  return nullptr;
-}
-
-template <typename... T> inline void _tzset(T...) {}
-}  // namespace fmt_detail
-
 FMT_BEGIN_NAMESPACE
 
 // Enable safe chrono durations, unless explicitly disabled.
@@ -341,7 +326,7 @@ inline auto get_classic_locale() -> const std::locale& {
 }
 
 template <typename CodeUnit> struct codecvt_result {
-  static constexpr const size_t max_size = 32;
+  static constexpr size_t max_size = 32;
   CodeUnit buf[max_size];
   CodeUnit* end;
 };
@@ -435,14 +420,11 @@ auto write(OutputIt out, const std::tm& time, const std::locale& loc,
   return write_encoded_tm_str(out, string_view(buf.data(), buf.size()), loc);
 }
 
-template <typename Rep1, typename Rep2>
-struct is_same_arithmetic_type
-    : public std::integral_constant<bool,
-                                    (std::is_integral<Rep1>::value &&
-                                     std::is_integral<Rep2>::value) ||
-                                        (std::is_floating_point<Rep1>::value &&
-                                         std::is_floating_point<Rep2>::value)> {
-};
+template <typename T, typename U>
+using is_similar_arithmetic_type =
+    bool_constant<(std::is_integral<T>::value && std::is_integral<U>::value) ||
+                  (std::is_floating_point<T>::value &&
+                   std::is_floating_point<U>::value)>;
 
 FMT_NORETURN inline void throw_duration_error() {
   FMT_THROW(format_error("cannot format duration"));
@@ -501,9 +483,9 @@ auto duration_cast(std::chrono::duration<FromRep, FromPeriod> from) -> To {
 #endif
 }
 
-template <
-    typename To, typename FromRep, typename FromPeriod,
-    FMT_ENABLE_IF(!is_same_arithmetic_type<FromRep, typename To::rep>::value)>
+template <typename To, typename FromRep, typename FromPeriod,
+          FMT_ENABLE_IF(
+              !is_similar_arithmetic_type<FromRep, typename To::rep>::value)>
 auto duration_cast(std::chrono::duration<FromRep, FromPeriod> from) -> To {
   // Mixed integer <-> float cast is not supported by safe_duration_cast.
   return std::chrono::duration_cast<To>(from);
@@ -519,12 +501,30 @@ auto to_time_t(sys_time<Duration> time_point) -> std::time_t {
       .count();
 }
 
-// Workaround a bug in libstdc++ which sets __cpp_lib_chrono to 201907 without
-// providing current_zone(): https://github.com/fmtlib/fmt/issues/4160.
-template <typename T> FMT_CONSTEXPR auto has_current_zone() -> bool {
-  using namespace std::chrono;
-  using namespace fmt_detail;
-  return !std::is_same<decltype(current_zone()), fmt_detail::time_zone*>::value;
+namespace tz {
+
+// DEPRECATED!
+struct time_zone {
+  template <typename Duration, typename LocalTime>
+  auto to_sys(LocalTime) -> sys_time<Duration> {
+    return {};
+  }
+};
+template <typename... T> auto current_zone(T...) -> time_zone* {
+  return nullptr;
+}
+
+template <typename... T> void _tzset(T...) {}
+}  // namespace tz
+
+// DEPRECATED!
+inline void tzset_once() {
+  static bool init = []() {
+    using namespace tz;
+    _tzset();
+    return false;
+  }();
+  ignore_unused(init);
 }
 }  // namespace detail
 
@@ -535,7 +535,7 @@ FMT_BEGIN_EXPORT
  * expressed in local time. Unlike `std::localtime`, this function is
  * thread-safe on most platforms.
  */
-inline auto localtime(std::time_t time) -> std::tm {
+FMT_DEPRECATED inline auto localtime(std::time_t time) -> std::tm {
   struct dispatcher {
     std::time_t time_;
     std::tm tm_;
@@ -572,11 +572,11 @@ inline auto localtime(std::time_t time) -> std::tm {
 }
 
 #if FMT_USE_LOCAL_TIME
-template <typename Duration,
-          FMT_ENABLE_IF(detail::has_current_zone<Duration>())>
-inline auto localtime(std::chrono::local_time<Duration> time) -> std::tm {
+template <typename Duration>
+FMT_DEPRECATED auto localtime(std::chrono::local_time<Duration> time)
+    -> std::tm {
   using namespace std::chrono;
-  using namespace fmt_detail;
+  using namespace detail::tz;
   return localtime(detail::to_time_t(current_zone()->to_sys<Duration>(time)));
 }
 #endif
@@ -652,7 +652,7 @@ inline void write_digit2_separated(char* buf, unsigned a, unsigned b,
   // Add ASCII '0' to each digit byte and insert separators.
   digits |= 0x3030003030003030 | (usep << 16) | (usep << 40);
 
-  constexpr const size_t len = 8;
+  constexpr size_t len = 8;
   if (const_check(is_big_endian())) {
     char tmp[len];
     std::memcpy(tmp, &digits, len);
@@ -911,7 +911,14 @@ template <typename Derived> struct null_chrono_spec_handler {
   FMT_CONSTEXPR void on_tz_name() { unsupported(); }
 };
 
-struct tm_format_checker : null_chrono_spec_handler<tm_format_checker> {
+class tm_format_checker : public null_chrono_spec_handler<tm_format_checker> {
+ private:
+  bool has_timezone_ = false;
+
+ public:
+  constexpr explicit tm_format_checker(bool has_timezone)
+      : has_timezone_(has_timezone) {}
+
   FMT_NORETURN inline void unsupported() {
     FMT_THROW(format_error("no format"));
   }
@@ -949,8 +956,12 @@ struct tm_format_checker : null_chrono_spec_handler<tm_format_checker> {
   FMT_CONSTEXPR void on_24_hour_time() {}
   FMT_CONSTEXPR void on_iso_time() {}
   FMT_CONSTEXPR void on_am_pm() {}
-  FMT_CONSTEXPR void on_utc_offset(numeric_system) {}
-  FMT_CONSTEXPR void on_tz_name() {}
+  FMT_CONSTEXPR void on_utc_offset(numeric_system) {
+    if (!has_timezone_) FMT_THROW(format_error("no timezone"));
+  }
+  FMT_CONSTEXPR void on_tz_name() {
+    if (!has_timezone_) FMT_THROW(format_error("no timezone"));
+  }
 };
 
 inline auto tm_wday_full_name(int wday) -> const char* {
@@ -980,24 +991,27 @@ inline auto tm_mon_short_name(int mon) -> const char* {
 }
 
 template <typename T, typename = void>
-struct has_member_data_tm_gmtoff : std::false_type {};
+struct has_tm_gmtoff : std::false_type {};
 template <typename T>
-struct has_member_data_tm_gmtoff<T, void_t<decltype(T::tm_gmtoff)>>
-    : std::true_type {};
+struct has_tm_gmtoff<T, void_t<decltype(T::tm_gmtoff)>> : std::true_type {};
 
-template <typename T, typename = void>
-struct has_member_data_tm_zone : std::false_type {};
+template <typename T, typename = void> struct has_tm_zone : std::false_type {};
 template <typename T>
-struct has_member_data_tm_zone<T, void_t<decltype(T::tm_zone)>>
-    : std::true_type {};
+struct has_tm_zone<T, void_t<decltype(T::tm_zone)>> : std::true_type {};
 
-inline void tzset_once() {
-  static bool init = []() {
-    using namespace fmt_detail;
-    _tzset();
-    return false;
-  }();
-  ignore_unused(init);
+template <typename T, FMT_ENABLE_IF(has_tm_zone<T>::value)>
+bool set_tm_zone(T& time, char* tz) {
+  time.tm_zone = tz;
+  return true;
+}
+template <typename T, FMT_ENABLE_IF(!has_tm_zone<T>::value)>
+bool set_tm_zone(T&, char*) {
+  return false;
+}
+
+inline char* utc() {
+  static char tz[] = "UTC";
+  return tz;
 }
 
 // Converts value to Int and checks that it's in the range [0, upper).
@@ -1005,7 +1019,7 @@ template <typename T, typename Int, FMT_ENABLE_IF(std::is_integral<T>::value)>
 inline auto to_nonnegative_int(T value, Int upper) -> Int {
   if (!std::is_unsigned<Int>::value &&
       (value < 0 || to_unsigned(value) > to_unsigned(upper))) {
-    FMT_THROW(fmt::format_error("chrono value is out of range"));
+    FMT_THROW(format_error("chrono value is out of range"));
   }
   return static_cast<Int>(value);
 }
@@ -1090,7 +1104,7 @@ void write_fractional_seconds(OutputIt& out, Duration d, int precision = -1) {
 
 // Format subseconds which are given as a floating point type with an
 // appropriate number of digits. We cannot pass the Duration here, as we
-// explicitly need to pass the Rep value in the chrono_formatter.
+// explicitly need to pass the Rep value in the duration_formatter.
 template <typename Duration>
 void write_floating_seconds(memory_buffer& buf, Duration duration,
                             int num_fractional_digits = -1) {
@@ -1124,7 +1138,7 @@ class tm_writer {
   static constexpr int days_per_week = 7;
 
   const std::locale& loc_;
-  const bool is_classic_;
+  bool is_classic_;
   OutputIt out_;
   const Duration* subsecs_;
   const std::tm& tm_;
@@ -1160,8 +1174,8 @@ class tm_writer {
   }
 
   auto tm_hour12() const noexcept -> int {
-    const auto h = tm_hour();
-    const auto z = h < 12 ? h : h - 12;
+    auto h = tm_hour();
+    auto z = h < 12 ? h : h - 12;
     return z == 0 ? 12 : z;
   }
 
@@ -1177,11 +1191,11 @@ class tm_writer {
 
   // Algorithm: https://en.wikipedia.org/wiki/ISO_week_date.
   auto iso_year_weeks(long long curr_year) const noexcept -> int {
-    const auto prev_year = curr_year - 1;
-    const auto curr_p =
+    auto prev_year = curr_year - 1;
+    auto curr_p =
         (curr_year + curr_year / 4 - curr_year / 100 + curr_year / 400) %
         days_per_week;
-    const auto prev_p =
+    auto prev_p =
         (prev_year + prev_year / 4 - prev_year / 100 + prev_year / 400) %
         days_per_week;
     return 52 + ((curr_p == 4 || prev_p == 3) ? 1 : 0);
@@ -1191,15 +1205,15 @@ class tm_writer {
            days_per_week;
   }
   auto tm_iso_week_year() const noexcept -> long long {
-    const auto year = tm_year();
-    const auto w = iso_week_num(tm_yday(), tm_wday());
+    auto year = tm_year();
+    auto w = iso_week_num(tm_yday(), tm_wday());
     if (w < 1) return year - 1;
     if (w > iso_year_weeks(year)) return year + 1;
     return year;
   }
   auto tm_iso_week_of_year() const noexcept -> int {
-    const auto year = tm_year();
-    const auto w = iso_week_num(tm_yday(), tm_wday());
+    auto year = tm_year();
+    auto w = iso_week_num(tm_yday(), tm_wday());
     if (w < 1) return iso_year_weeks(year - 1);
     if (w > iso_year_weeks(year)) return 1;
     return w;
@@ -1236,9 +1250,8 @@ class tm_writer {
     uint32_or_64_or_128_t<long long> n = to_unsigned(year);
     const int num_digits = count_digits(n);
     if (negative && pad == pad_type::zero) *out_++ = '-';
-    if (width > num_digits) {
+    if (width > num_digits)
       out_ = detail::write_padding(out_, pad, width - num_digits);
-    }
     if (negative && pad != pad_type::zero) *out_++ = '-';
     out_ = format_decimal<Char>(out_, n, num_digits);
   }
@@ -1259,45 +1272,22 @@ class tm_writer {
     write2(static_cast<int>(offset % 60));
   }
 
-  template <typename T, FMT_ENABLE_IF(has_member_data_tm_gmtoff<T>::value)>
-  void format_utc_offset_impl(const T& tm, numeric_system ns) {
+  template <typename T, FMT_ENABLE_IF(has_tm_gmtoff<T>::value)>
+  void format_utc_offset(const T& tm, numeric_system ns) {
     write_utc_offset(tm.tm_gmtoff, ns);
   }
-  template <typename T, FMT_ENABLE_IF(!has_member_data_tm_gmtoff<T>::value)>
-  void format_utc_offset_impl(const T& tm, numeric_system ns) {
-#if defined(_WIN32) && defined(_UCRT)
-    tzset_once();
-    long offset = 0;
-    _get_timezone(&offset);
-    if (tm.tm_isdst) {
-      long dstbias = 0;
-      _get_dstbias(&dstbias);
-      offset += dstbias;
-    }
-    write_utc_offset(-offset, ns);
-#else
-    if (ns == numeric_system::standard) return format_localized('z');
-
-    // Extract timezone offset from timezone conversion functions.
-    std::tm gtm = tm;
-    std::time_t gt = std::mktime(&gtm);
-    std::tm ltm = gmtime(gt);
-    std::time_t lt = std::mktime(&ltm);
-    long long offset = gt - lt;
-    write_utc_offset(offset, ns);
-#endif
+  template <typename T, FMT_ENABLE_IF(!has_tm_gmtoff<T>::value)>
+  void format_utc_offset(const T&, numeric_system ns) {
+    write_utc_offset(0, ns);
   }
 
-  template <typename T, FMT_ENABLE_IF(has_member_data_tm_zone<T>::value)>
-  void format_tz_name_impl(const T& tm) {
-    if (is_classic_)
-      out_ = write_tm_str<Char>(out_, tm.tm_zone, loc_);
-    else
-      format_localized('Z');
+  template <typename T, FMT_ENABLE_IF(has_tm_zone<T>::value)>
+  void format_tz_name(const T& tm) {
+    out_ = write_tm_str<Char>(out_, tm.tm_zone, loc_);
   }
-  template <typename T, FMT_ENABLE_IF(!has_member_data_tm_zone<T>::value)>
-  void format_tz_name_impl(const T&) {
-    format_localized('Z');
+  template <typename T, FMT_ENABLE_IF(!has_tm_zone<T>::value)>
+  void format_tz_name(const T&) {
+    out_ = std::copy_n(utc(), 3, out_);
   }
 
   void format_localized(char format, char modifier = 0) {
@@ -1408,8 +1398,8 @@ class tm_writer {
     out_ = copy<Char>(std::begin(buf) + offset, std::end(buf), out_);
   }
 
-  void on_utc_offset(numeric_system ns) { format_utc_offset_impl(tm_, ns); }
-  void on_tz_name() { format_tz_name_impl(tm_); }
+  void on_utc_offset(numeric_system ns) { format_utc_offset(tm_, ns); }
+  void on_tz_name() { format_tz_name(tm_); }
 
   void on_year(numeric_system ns, pad_type pad) {
     if (is_classic_ || ns == numeric_system::standard)
@@ -1483,11 +1473,10 @@ class tm_writer {
   void on_day_of_year(pad_type pad) {
     auto yday = tm_yday() + 1;
     auto digit1 = yday / 100;
-    if (digit1 != 0) {
+    if (digit1 != 0)
       write1(digit1);
-    } else {
+    else
       out_ = detail::write_padding(out_, pad);
-    }
     write2(yday % 100, pad);
   }
 
@@ -1624,18 +1613,16 @@ template <typename Rep, typename Period,
           FMT_ENABLE_IF(std::is_integral<Rep>::value)>
 inline auto get_milliseconds(std::chrono::duration<Rep, Period> d)
     -> std::chrono::duration<Rep, std::milli> {
-  // this may overflow and/or the result may not fit in the
-  // target type.
+  // This may overflow and/or the result may not fit in the target type.
 #if FMT_SAFE_DURATION_CAST
-  using CommonSecondsType =
+  using common_seconds_type =
       typename std::common_type<decltype(d), std::chrono::seconds>::type;
-  const auto d_as_common = detail::duration_cast<CommonSecondsType>(d);
-  const auto d_as_whole_seconds =
+  auto d_as_common = detail::duration_cast<common_seconds_type>(d);
+  auto d_as_whole_seconds =
       detail::duration_cast<std::chrono::seconds>(d_as_common);
-  // this conversion should be nonproblematic
-  const auto diff = d_as_common - d_as_whole_seconds;
-  const auto ms =
-      detail::duration_cast<std::chrono::duration<Rep, std::milli>>(diff);
+  // This conversion should be nonproblematic.
+  auto diff = d_as_common - d_as_whole_seconds;
+  auto ms = detail::duration_cast<std::chrono::duration<Rep, std::milli>>(diff);
   return ms;
 #else
   auto s = detail::duration_cast<std::chrono::seconds>(d);
@@ -1707,32 +1694,28 @@ class get_locale {
   }
 };
 
-template <typename FormatContext, typename OutputIt, typename Rep,
-          typename Period>
-struct chrono_formatter {
-  FormatContext& context;
-  OutputIt out;
-  int precision;
-  bool localized = false;
+template <typename Char, typename Rep, typename Period>
+struct duration_formatter {
+  using iterator = basic_appender<Char>;
+  iterator out;
   // rep is unsigned to avoid overflow.
   using rep =
       conditional_t<std::is_integral<Rep>::value && sizeof(Rep) < sizeof(int),
                     unsigned, typename make_unsigned_or_unchanged<Rep>::type>;
   rep val;
+  int precision;
+  locale_ref locale;
+  bool localized = false;
   using seconds = std::chrono::duration<rep>;
   seconds s;
   using milliseconds = std::chrono::duration<rep, std::milli>;
   bool negative;
 
-  using char_type = typename FormatContext::char_type;
-  using tm_writer_type = tm_writer<OutputIt, char_type>;
+  using tm_writer_type = tm_writer<iterator, Char>;
 
-  chrono_formatter(FormatContext& ctx, OutputIt o,
-                   std::chrono::duration<Rep, Period> d)
-      : context(ctx),
-        out(o),
-        val(static_cast<rep>(d.count())),
-        negative(false) {
+  duration_formatter(iterator o, std::chrono::duration<Rep, Period> d,
+                     locale_ref loc)
+      : out(o), val(static_cast<rep>(d.count())), locale(loc), negative(false) {
     if (d.count() < 0) {
       val = 0 - val;
       negative = true;
@@ -1746,19 +1729,16 @@ struct chrono_formatter {
 
   // returns true if nan or inf, writes to out.
   auto handle_nan_inf() -> bool {
-    if (isfinite(val)) {
-      return false;
-    }
+    if (isfinite(val)) return false;
     if (isnan(val)) {
       write_nan();
       return true;
     }
     // must be +-inf
-    if (val > 0) {
-      write_pinf();
-    } else {
-      write_ninf();
-    }
+    if (val > 0)
+      std::copy_n("inf", 3, out);
+    else
+      std::copy_n("-inf", 4, out);
     return true;
   }
 
@@ -1786,10 +1766,9 @@ struct chrono_formatter {
   }
 
   void write_sign() {
-    if (negative) {
-      *out++ = '-';
-      negative = false;
-    }
+    if (!negative) return;
+    *out++ = '-';
+    negative = false;
   }
 
   void write(Rep value, int width, pad_type pad = pad_type::zero) {
@@ -1801,24 +1780,22 @@ struct chrono_formatter {
     if (width > num_digits) {
       out = detail::write_padding(out, pad, width - num_digits);
     }
-    out = format_decimal<char_type>(out, n, num_digits);
+    out = format_decimal<Char>(out, n, num_digits);
   }
 
   void write_nan() { std::copy_n("nan", 3, out); }
-  void write_pinf() { std::copy_n("inf", 3, out); }
-  void write_ninf() { std::copy_n("-inf", 4, out); }
 
   template <typename Callback, typename... Args>
   void format_tm(const tm& time, Callback cb, Args... args) {
     if (isnan(val)) return write_nan();
-    get_locale loc(localized, context.locale());
+    get_locale loc(localized, locale);
     auto w = tm_writer_type(loc, out, time);
     (w.*cb)(args...);
     out = w.out();
   }
 
-  void on_text(const char_type* begin, const char_type* end) {
-    copy<char_type>(begin, end, out);
+  void on_text(const Char* begin, const Char* end) {
+    copy<Char>(begin, end, out);
   }
 
   // These are not implemented because durations don't have date information.
@@ -1888,13 +1865,12 @@ struct chrono_formatter {
         write_floating_seconds(buf, std::chrono::duration<rep, Period>(val),
                                precision);
         if (negative) *out++ = '-';
-        if (buf.size() < 2 || buf[1] == '.') {
+        if (buf.size() < 2 || buf[1] == '.')
           out = detail::write_padding(out, pad);
-        }
-        out = copy<char_type>(buf.begin(), buf.end(), out);
+        out = copy<Char>(buf.begin(), buf.end(), out);
       } else {
         write(second(), 2, pad);
-        write_fractional_seconds<char_type>(
+        write_fractional_seconds<Char>(
             out, std::chrono::duration<rep, Period>(val), precision);
       }
       return;
@@ -1936,12 +1912,10 @@ struct chrono_formatter {
   void on_duration_value() {
     if (handle_nan_inf()) return;
     write_sign();
-    out = format_duration_value<char_type>(out, val, precision);
+    out = format_duration_value<Char>(out, val, precision);
   }
 
-  void on_duration_unit() {
-    out = format_duration_unit<char_type, Period>(out);
-  }
+  void on_duration_unit() { out = format_duration_unit<Char, Period>(out); }
 };
 
 }  // namespace detail
@@ -2011,12 +1985,11 @@ class year_month_day {
   constexpr auto month() const noexcept -> fmt::month { return month_; }
   constexpr auto day() const noexcept -> fmt::day { return day_; }
 };
-#endif
+#endif  // __cpp_lib_chrono >= 201907
 
 template <typename Char>
 struct formatter<weekday, Char> : private formatter<std::tm, Char> {
  private:
-  bool localized_ = false;
   bool use_tm_formatter_ = false;
 
  public:
@@ -2024,8 +1997,7 @@ struct formatter<weekday, Char> : private formatter<std::tm, Char> {
     auto it = ctx.begin(), end = ctx.end();
     if (it != end && *it == 'L') {
       ++it;
-      localized_ = true;
-      return it;
+      this->set_localized();
     }
     use_tm_formatter_ = it != end && *it != '}';
     return use_tm_formatter_ ? formatter<std::tm, Char>::parse(ctx) : it;
@@ -2036,7 +2008,7 @@ struct formatter<weekday, Char> : private formatter<std::tm, Char> {
     auto time = std::tm();
     time.tm_wday = static_cast<int>(wd.c_encoding());
     if (use_tm_formatter_) return formatter<std::tm, Char>::format(time, ctx);
-    detail::get_locale loc(localized_, ctx.locale());
+    detail::get_locale loc(this->localized(), ctx.locale());
     auto w = detail::tm_writer<decltype(ctx.out()), Char>(loc, ctx.out(), time);
     w.on_abbr_weekday();
     return w.out();
@@ -2070,7 +2042,6 @@ struct formatter<day, Char> : private formatter<std::tm, Char> {
 template <typename Char>
 struct formatter<month, Char> : private formatter<std::tm, Char> {
  private:
-  bool localized_ = false;
   bool use_tm_formatter_ = false;
 
  public:
@@ -2078,8 +2049,7 @@ struct formatter<month, Char> : private formatter<std::tm, Char> {
     auto it = ctx.begin(), end = ctx.end();
     if (it != end && *it == 'L') {
       ++it;
-      localized_ = true;
-      return it;
+      this->set_localized();
     }
     use_tm_formatter_ = it != end && *it != '}';
     return use_tm_formatter_ ? formatter<std::tm, Char>::parse(ctx) : it;
@@ -2090,7 +2060,7 @@ struct formatter<month, Char> : private formatter<std::tm, Char> {
     auto time = std::tm();
     time.tm_mon = static_cast<int>(static_cast<unsigned>(m)) - 1;
     if (use_tm_formatter_) return formatter<std::tm, Char>::format(time, ctx);
-    detail::get_locale loc(localized_, ctx.locale());
+    detail::get_locale loc(this->localized(), ctx.locale());
     auto w = detail::tm_writer<decltype(ctx.out()), Char>(loc, ctx.out(), time);
     w.on_abbr_month();
     return w.out();
@@ -2154,7 +2124,6 @@ struct formatter<std::chrono::duration<Rep, Period>, Char> {
   format_specs specs_;
   detail::arg_ref<Char> width_ref_;
   detail::arg_ref<Char> precision_ref_;
-  bool localized_ = false;
   basic_string_view<Char> fmt_;
 
  public:
@@ -2177,7 +2146,7 @@ struct formatter<std::chrono::duration<Rep, Period>, Char> {
       it = detail::parse_precision(it, end, specs_, precision_ref_, ctx);
     }
     if (it != end && *it == 'L') {
-      localized_ = true;
+      specs_.set_localized();
       ++it;
     }
     end = detail::parse_chrono_format(it, end, checker);
@@ -2204,11 +2173,10 @@ struct formatter<std::chrono::duration<Rep, Period>, Char> {
       out = detail::format_duration_value<Char>(out, d.count(), precision);
       detail::format_duration_unit<Char, Period>(out);
     } else {
-      using chrono_formatter =
-          detail::chrono_formatter<FormatContext, decltype(out), Rep, Period>;
-      auto f = chrono_formatter(ctx, out, d);
+      auto f =
+          detail::duration_formatter<Char, Rep, Period>(out, d, ctx.locale());
       f.precision = precision;
-      f.localized = localized_;
+      f.localized = specs_.localized();
       detail::parse_chrono_format(begin, end, f);
     }
     return detail::write(
@@ -2220,30 +2188,15 @@ template <typename Char> struct formatter<std::tm, Char> {
  private:
   format_specs specs_;
   detail::arg_ref<Char> width_ref_;
+  basic_string_view<Char> fmt_ =
+      detail::string_literal<Char, '%', 'F', ' ', '%', 'T'>();
 
  protected:
-  basic_string_view<Char> fmt_;
+  auto localized() const -> bool { return specs_.localized(); }
+  FMT_CONSTEXPR void set_localized() { specs_.set_localized(); }
 
-  template <typename Duration, typename FormatContext>
-  auto do_format(const std::tm& tm, FormatContext& ctx,
-                 const Duration* subsecs) const -> decltype(ctx.out()) {
-    auto specs = specs_;
-    auto buf = basic_memory_buffer<Char>();
-    auto out = basic_appender<Char>(buf);
-    detail::handle_dynamic_spec(specs.dynamic_width(), specs.width, width_ref_,
-                                ctx);
-
-    auto loc_ref = ctx.locale();
-    detail::get_locale loc(static_cast<bool>(loc_ref), loc_ref);
-    auto w =
-        detail::tm_writer<decltype(out), Char, Duration>(loc, out, tm, subsecs);
-    detail::parse_chrono_format(fmt_.begin(), fmt_.end(), w);
-    return detail::write(
-        ctx.out(), basic_string_view<Char>(buf.data(), buf.size()), specs);
-  }
-
- public:
-  FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) -> const Char* {
+  FMT_CONSTEXPR auto do_parse(parse_context<Char>& ctx, bool has_timezone)
+      -> const Char* {
     auto it = ctx.begin(), end = ctx.end();
     if (it == end || *it == '}') return it;
 
@@ -2256,12 +2209,41 @@ template <typename Char> struct formatter<std::tm, Char> {
       if (it == end) return it;
     }
 
-    end = detail::parse_chrono_format(it, end, detail::tm_format_checker());
+    if (*it == 'L') {
+      specs_.set_localized();
+      ++it;
+    }
+
+    end = detail::parse_chrono_format(it, end,
+                                      detail::tm_format_checker(has_timezone));
     // Replace the default format string only if the new spec is not empty.
     if (end != it) fmt_ = {it, detail::to_unsigned(end - it)};
     return end;
   }
 
+  template <typename Duration, typename FormatContext>
+  auto do_format(const std::tm& tm, FormatContext& ctx,
+                 const Duration* subsecs) const -> decltype(ctx.out()) {
+    auto specs = specs_;
+    auto buf = basic_memory_buffer<Char>();
+    auto out = basic_appender<Char>(buf);
+    detail::handle_dynamic_spec(specs.dynamic_width(), specs.width, width_ref_,
+                                ctx);
+
+    auto loc_ref = specs.localized() ? ctx.locale() : detail::locale_ref();
+    detail::get_locale loc(static_cast<bool>(loc_ref), loc_ref);
+    auto w = detail::tm_writer<basic_appender<Char>, Char, Duration>(
+        loc, out, tm, subsecs);
+    detail::parse_chrono_format(fmt_.begin(), fmt_.end(), w);
+    return detail::write(
+        ctx.out(), basic_string_view<Char>(buf.data(), buf.size()), specs);
+  }
+
+ public:
+  FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) -> const Char* {
+    return do_parse(ctx, detail::has_tm_gmtoff<std::tm>::value);
+  }
+
   template <typename FormatContext>
   auto format(const std::tm& tm, FormatContext& ctx) const
       -> decltype(ctx.out()) {
@@ -2269,10 +2251,11 @@ template <typename Char> struct formatter<std::tm, Char> {
   }
 };
 
+// DEPRECATED! Reversed order of template parameters.
 template <typename Char, typename Duration>
-struct formatter<sys_time<Duration>, Char> : formatter<std::tm, Char> {
-  FMT_CONSTEXPR formatter() {
-    this->fmt_ = detail::string_literal<Char, '%', 'F', ' ', '%', 'T'>();
+struct formatter<sys_time<Duration>, Char> : private formatter<std::tm, Char> {
+  FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) -> const Char* {
+    return this->do_parse(ctx, true);
   }
 
   template <typename FormatContext>
@@ -2283,6 +2266,7 @@ struct formatter<sys_time<Duration>, Char> : formatter<std::tm, Char> {
     if (detail::const_check(
             period::num == 1 && period::den == 1 &&
             !std::is_floating_point<typename Duration::rep>::value)) {
+      detail::set_tm_zone(tm, detail::utc());
       return formatter<std::tm, Char>::format(tm, ctx);
     }
     Duration epoch = val.time_since_epoch();
@@ -2290,11 +2274,13 @@ struct formatter<sys_time<Duration>, Char> : formatter<std::tm, Char> {
         epoch - detail::duration_cast<std::chrono::seconds>(epoch));
     if (subsecs.count() < 0) {
       auto second = detail::duration_cast<Duration>(std::chrono::seconds(1));
-      if (tm.tm_sec != 0)
+      if (tm.tm_sec != 0) {
         --tm.tm_sec;
-      else
+      } else {
         tm = gmtime(val - second);
-      subsecs += detail::duration_cast<Duration>(std::chrono::seconds(1));
+        detail::set_tm_zone(tm, detail::utc());
+      }
+      subsecs += second;
     }
     return formatter<std::tm, Char>::do_format(tm, ctx, &subsecs);
   }
@@ -2312,23 +2298,29 @@ struct formatter<utc_time<Duration>, Char>
 };
 
 template <typename Duration, typename Char>
-struct formatter<local_time<Duration>, Char> : formatter<std::tm, Char> {
-  FMT_CONSTEXPR formatter() {
-    this->fmt_ = detail::string_literal<Char, '%', 'F', ' ', '%', 'T'>();
+struct formatter<local_time<Duration>, Char>
+    : private formatter<std::tm, Char> {
+  FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) -> const Char* {
+    return this->do_parse(ctx, false);
   }
 
   template <typename FormatContext>
   auto format(local_time<Duration> val, FormatContext& ctx) const
       -> decltype(ctx.out()) {
+    auto time_since_epoch = val.time_since_epoch();
+    auto seconds_since_epoch =
+        detail::duration_cast<std::chrono::seconds>(time_since_epoch);
+    // Use gmtime to prevent time zone conversion since local_time has an
+    // unspecified time zone.
+    std::tm t = gmtime(seconds_since_epoch.count());
     using period = typename Duration::period;
     if (period::num == 1 && period::den == 1 &&
         !std::is_floating_point<typename Duration::rep>::value) {
-      return formatter<std::tm, Char>::format(localtime(val), ctx);
+      return formatter<std::tm, Char>::format(t, ctx);
     }
-    auto epoch = val.time_since_epoch();
-    auto subsecs = detail::duration_cast<Duration>(
-        epoch - detail::duration_cast<std::chrono::seconds>(epoch));
-    return formatter<std::tm, Char>::do_format(localtime(val), ctx, &subsecs);
+    auto subsecs =
+        detail::duration_cast<Duration>(time_since_epoch - seconds_since_epoch);
+    return formatter<std::tm, Char>::do_format(t, ctx, &subsecs);
   }
 };
 
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/color.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/color.h
index 2faaf3a067..638f15b43f 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/color.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/color.h
@@ -190,11 +190,11 @@ enum class emphasis : uint8_t {
 // rgb is a struct for red, green and blue colors.
 // Using the name "rgb" makes some editors show the color in a tooltip.
 struct rgb {
-  FMT_CONSTEXPR rgb() : r(0), g(0), b(0) {}
-  FMT_CONSTEXPR rgb(uint8_t r_, uint8_t g_, uint8_t b_) : r(r_), g(g_), b(b_) {}
-  FMT_CONSTEXPR rgb(uint32_t hex)
+  constexpr rgb() : r(0), g(0), b(0) {}
+  constexpr rgb(uint8_t r_, uint8_t g_, uint8_t b_) : r(r_), g(g_), b(b_) {}
+  constexpr rgb(uint32_t hex)
       : r((hex >> 16) & 0xFF), g((hex >> 8) & 0xFF), b(hex & 0xFF) {}
-  FMT_CONSTEXPR rgb(color hex)
+  constexpr rgb(color hex)
       : r((uint32_t(hex) >> 16) & 0xFF),
         g((uint32_t(hex) >> 8) & 0xFF),
         b(uint32_t(hex) & 0xFF) {}
@@ -205,97 +205,135 @@ struct rgb {
 
 namespace detail {
 
-// color is a struct of either a rgb color or a terminal color.
+// A bit-packed variant of an RGB color, a terminal color, or unset color.
+// see text_style for the bit-packing scheme.
 struct color_type {
-  FMT_CONSTEXPR color_type() noexcept : is_rgb(), value{} {}
-  FMT_CONSTEXPR color_type(color rgb_color) noexcept : is_rgb(true), value{} {
-    value.rgb_color = static_cast<uint32_t>(rgb_color);
+  constexpr color_type() noexcept = default;
+  constexpr color_type(color rgb_color) noexcept
+      : value_(static_cast<uint32_t>(rgb_color) | (1 << 24)) {}
+  constexpr color_type(rgb rgb_color) noexcept
+      : color_type(static_cast<color>(
+            (static_cast<uint32_t>(rgb_color.r) << 16) |
+            (static_cast<uint32_t>(rgb_color.g) << 8) | rgb_color.b)) {}
+  constexpr color_type(terminal_color term_color) noexcept
+      : value_(static_cast<uint32_t>(term_color) | (3 << 24)) {}
+
+  constexpr auto is_terminal_color() const noexcept -> bool {
+    return (value_ & (1 << 25)) != 0;
   }
-  FMT_CONSTEXPR color_type(rgb rgb_color) noexcept : is_rgb(true), value{} {
-    value.rgb_color = (static_cast<uint32_t>(rgb_color.r) << 16) |
-                      (static_cast<uint32_t>(rgb_color.g) << 8) | rgb_color.b;
+
+  constexpr auto value() const noexcept -> uint32_t {
+    return value_ & 0xFFFFFF;
   }
-  FMT_CONSTEXPR color_type(terminal_color term_color) noexcept
-      : is_rgb(), value{} {
-    value.term_color = static_cast<uint8_t>(term_color);
-  }
-  bool is_rgb;
-  union color_union {
-    uint8_t term_color;
-    uint32_t rgb_color;
-  } value;
+
+  constexpr color_type(uint32_t value) noexcept : value_(value) {}
+
+  uint32_t value_ = 0;
 };
 }  // namespace detail
 
 /// A text style consisting of foreground and background colors and emphasis.
 class text_style {
+  // The information is packed as follows:
+  // ┌──┐
+  // │ 0│─┐
+  // │..│ ├── foreground color value
+  // │23│─┘
+  // ├──┤
+  // │24│─┬── discriminator for the above value. 00 if unset, 01 if it's
+  // │25│─┘   an RGB color, or 11 if it's a terminal color (10 is unused)
+  // ├──┤
+  // │26│──── overflow bit, always zero (see below)
+  // ├──┤
+  // │27│─┐
+  // │..│ │
+  // │50│ │
+  // ├──┤ │
+  // │51│ ├── background color (same format as the foreground color)
+  // │52│ │
+  // ├──┤ │
+  // │53│─┘
+  // ├──┤
+  // │54│─┐
+  // │..│ ├── emphases
+  // │61│─┘
+  // ├──┤
+  // │62│─┬── unused
+  // │63│─┘
+  // └──┘
+  // The overflow bits are there to make operator|= efficient.
+  // When ORing, we must throw if, for either the foreground or background,
+  // one style specifies a terminal color and the other specifies any color
+  // (terminal or RGB); in other words, if one discriminator is 11 and the
+  // other is 11 or 01.
+  //
+  // We do that check by adding the styles. Consider what adding does to each
+  // possible pair of discriminators:
+  //    00 + 00 = 000
+  //    01 + 00 = 001
+  //    11 + 00 = 011
+  //    01 + 01 = 010
+  //    11 + 01 = 100 (!!)
+  //    11 + 11 = 110 (!!)
+  // In the last two cases, the ones we want to catch, the third bit——the
+  // overflow bit——is set. Bingo.
+  //
+  // We must take into account the possible carry bit from the bits
+  // before the discriminator. The only potentially problematic case is
+  // 11 + 00 = 011 (a carry bit would make it 100, not good!), but a carry
+  // bit is impossible in that case, because 00 (unset color) means the
+  // 24 bits that precede the discriminator are all zero.
+  //
+  // This test can be applied to both colors simultaneously.
+
  public:
   FMT_CONSTEXPR text_style(emphasis em = emphasis()) noexcept
-      : set_foreground_color(), set_background_color(), ems(em) {}
+      : style_(static_cast<uint64_t>(em) << 54) {}
 
-  FMT_CONSTEXPR auto operator|=(const text_style& rhs) -> text_style& {
-    if (!set_foreground_color) {
-      set_foreground_color = rhs.set_foreground_color;
-      foreground_color = rhs.foreground_color;
-    } else if (rhs.set_foreground_color) {
-      if (!foreground_color.is_rgb || !rhs.foreground_color.is_rgb)
-        report_error("can't OR a terminal color");
-      foreground_color.value.rgb_color |= rhs.foreground_color.value.rgb_color;
-    }
-
-    if (!set_background_color) {
-      set_background_color = rhs.set_background_color;
-      background_color = rhs.background_color;
-    } else if (rhs.set_background_color) {
-      if (!background_color.is_rgb || !rhs.background_color.is_rgb)
-        report_error("can't OR a terminal color");
-      background_color.value.rgb_color |= rhs.background_color.value.rgb_color;
-    }
-
-    ems = static_cast<emphasis>(static_cast<uint8_t>(ems) |
-                                static_cast<uint8_t>(rhs.ems));
+  FMT_CONSTEXPR auto operator|=(text_style rhs) -> text_style& {
+    if (((style_ + rhs.style_) & ((1ULL << 26) | (1ULL << 53))) != 0)
+      report_error("can't OR a terminal color");
+    style_ |= rhs.style_;
     return *this;
   }
 
-  friend FMT_CONSTEXPR auto operator|(text_style lhs, const text_style& rhs)
+  friend FMT_CONSTEXPR auto operator|(text_style lhs, text_style rhs)
       -> text_style {
     return lhs |= rhs;
   }
 
+  FMT_CONSTEXPR auto operator==(text_style rhs) const noexcept -> bool {
+    return style_ == rhs.style_;
+  }
+
+  FMT_CONSTEXPR auto operator!=(text_style rhs) const noexcept -> bool {
+    return !(*this == rhs);
+  }
+
   FMT_CONSTEXPR auto has_foreground() const noexcept -> bool {
-    return set_foreground_color;
+    return (style_ & (1 << 24)) != 0;
   }
   FMT_CONSTEXPR auto has_background() const noexcept -> bool {
-    return set_background_color;
+    return (style_ & (1ULL << 51)) != 0;
   }
   FMT_CONSTEXPR auto has_emphasis() const noexcept -> bool {
-    return static_cast<uint8_t>(ems) != 0;
+    return (style_ >> 54) != 0;
   }
   FMT_CONSTEXPR auto get_foreground() const noexcept -> detail::color_type {
     FMT_ASSERT(has_foreground(), "no foreground specified for this style");
-    return foreground_color;
+    return style_ & 0x3FFFFFF;
   }
   FMT_CONSTEXPR auto get_background() const noexcept -> detail::color_type {
     FMT_ASSERT(has_background(), "no background specified for this style");
-    return background_color;
+    return (style_ >> 27) & 0x3FFFFFF;
   }
   FMT_CONSTEXPR auto get_emphasis() const noexcept -> emphasis {
     FMT_ASSERT(has_emphasis(), "no emphasis specified for this style");
-    return ems;
+    return static_cast<emphasis>(style_ >> 54);
   }
 
  private:
-  FMT_CONSTEXPR text_style(bool is_foreground,
-                           detail::color_type text_color) noexcept
-      : set_foreground_color(), set_background_color(), ems() {
-    if (is_foreground) {
-      foreground_color = text_color;
-      set_foreground_color = true;
-    } else {
-      background_color = text_color;
-      set_background_color = true;
-    }
-  }
+  FMT_CONSTEXPR text_style(uint64_t style) noexcept : style_(style) {}
 
   friend FMT_CONSTEXPR auto fg(detail::color_type foreground) noexcept
       -> text_style;
@@ -303,23 +341,19 @@ class text_style {
   friend FMT_CONSTEXPR auto bg(detail::color_type background) noexcept
       -> text_style;
 
-  detail::color_type foreground_color;
-  detail::color_type background_color;
-  bool set_foreground_color;
-  bool set_background_color;
-  emphasis ems;
+  uint64_t style_ = 0;
 };
 
 /// Creates a text style from the foreground (text) color.
 FMT_CONSTEXPR inline auto fg(detail::color_type foreground) noexcept
     -> text_style {
-  return text_style(true, foreground);
+  return foreground.value_;
 }
 
 /// Creates a text style from the background color.
 FMT_CONSTEXPR inline auto bg(detail::color_type background) noexcept
     -> text_style {
-  return text_style(false, background);
+  return static_cast<uint64_t>(background.value_) << 27;
 }
 
 FMT_CONSTEXPR inline auto operator|(emphasis lhs, emphasis rhs) noexcept
@@ -334,9 +368,9 @@ template <typename Char> struct ansi_color_escape {
                                   const char* esc) noexcept {
     // If we have a terminal color, we need to output another escape code
     // sequence.
-    if (!text_color.is_rgb) {
+    if (text_color.is_terminal_color()) {
       bool is_background = esc == string_view("\x1b[48;2;");
-      uint32_t value = text_color.value.term_color;
+      uint32_t value = text_color.value();
       // Background ASCII codes are the same as the foreground ones but with
       // 10 more.
       if (is_background) value += 10u;
@@ -360,7 +394,7 @@ template <typename Char> struct ansi_color_escape {
     for (int i = 0; i < 7; i++) {
       buffer[i] = static_cast<Char>(esc[i]);
     }
-    rgb color(text_color.value.rgb_color);
+    rgb color(text_color.value());
     to_esc(color.r, buffer + 7, ';');
     to_esc(color.g, buffer + 11, ';');
     to_esc(color.b, buffer + 15, 'm');
@@ -441,32 +475,26 @@ template <typename T> struct styled_arg : view {
 };
 
 template <typename Char>
-void vformat_to(buffer<Char>& buf, const text_style& ts,
-                basic_string_view<Char> fmt,
+void vformat_to(buffer<Char>& buf, text_style ts, basic_string_view<Char> fmt,
                 basic_format_args<buffered_context<Char>> args) {
-  bool has_style = false;
   if (ts.has_emphasis()) {
-    has_style = true;
     auto emphasis = make_emphasis<Char>(ts.get_emphasis());
     buf.append(emphasis.begin(), emphasis.end());
   }
   if (ts.has_foreground()) {
-    has_style = true;
     auto foreground = make_foreground_color<Char>(ts.get_foreground());
     buf.append(foreground.begin(), foreground.end());
   }
   if (ts.has_background()) {
-    has_style = true;
     auto background = make_background_color<Char>(ts.get_background());
     buf.append(background.begin(), background.end());
   }
   vformat_to(buf, fmt, args);
-  if (has_style) reset_color<Char>(buf);
+  if (ts != text_style()) reset_color<Char>(buf);
 }
 }  // namespace detail
 
-inline void vprint(FILE* f, const text_style& ts, string_view fmt,
-                   format_args args) {
+inline void vprint(FILE* f, text_style ts, string_view fmt, format_args args) {
   auto buf = memory_buffer();
   detail::vformat_to(buf, ts, fmt, args);
   print(f, FMT_STRING("{}"), string_view(buf.begin(), buf.size()));
@@ -482,8 +510,7 @@ inline void vprint(FILE* f, const text_style& ts, string_view fmt,
  *                "Elapsed time: {0:.2f} seconds", 1.23);
  */
 template <typename... T>
-void print(FILE* f, const text_style& ts, format_string<T...> fmt,
-           T&&... args) {
+void print(FILE* f, text_style ts, format_string<T...> fmt, T&&... args) {
   vprint(f, ts, fmt.str, vargs<T...>{{args...}});
 }
 
@@ -497,11 +524,11 @@ void print(FILE* f, const text_style& ts, format_string<T...> fmt,
  *                "Elapsed time: {0:.2f} seconds", 1.23);
  */
 template <typename... T>
-void print(const text_style& ts, format_string<T...> fmt, T&&... args) {
+void print(text_style ts, format_string<T...> fmt, T&&... args) {
   return print(stdout, ts, fmt, std::forward<T>(args)...);
 }
 
-inline auto vformat(const text_style& ts, string_view fmt, format_args args)
+inline auto vformat(text_style ts, string_view fmt, format_args args)
     -> std::string {
   auto buf = memory_buffer();
   detail::vformat_to(buf, ts, fmt, args);
@@ -521,7 +548,7 @@ inline auto vformat(const text_style& ts, string_view fmt, format_args args)
  * ```
  */
 template <typename... T>
-inline auto format(const text_style& ts, format_string<T...> fmt, T&&... args)
+inline auto format(text_style ts, format_string<T...> fmt, T&&... args)
     -> std::string {
   return fmt::vformat(ts, fmt.str, vargs<T...>{{args...}});
 }
@@ -529,8 +556,8 @@ inline auto format(const text_style& ts, format_string<T...> fmt, T&&... args)
 /// Formats a string with the given text_style and writes the output to `out`.
 template <typename OutputIt,
           FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, char>::value)>
-auto vformat_to(OutputIt out, const text_style& ts, string_view fmt,
-                format_args args) -> OutputIt {
+auto vformat_to(OutputIt out, text_style ts, string_view fmt, format_args args)
+    -> OutputIt {
   auto&& buf = detail::get_buffer<char>(out);
   detail::vformat_to(buf, ts, fmt, args);
   return detail::get_iterator(buf, out);
@@ -548,8 +575,8 @@ auto vformat_to(OutputIt out, const text_style& ts, string_view fmt,
  */
 template <typename OutputIt, typename... T,
           FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, char>::value)>
-inline auto format_to(OutputIt out, const text_style& ts,
-                      format_string<T...> fmt, T&&... args) -> OutputIt {
+inline auto format_to(OutputIt out, text_style ts, format_string<T...> fmt,
+                      T&&... args) -> OutputIt {
   return vformat_to(out, ts, fmt.str, vargs<T...>{{args...}});
 }
 
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/compile.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/compile.h
index 08d9427ff2..af7877185c 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/compile.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/compile.h
@@ -42,7 +42,7 @@ namespace detail {
 #endif
 
 template <typename T, typename... Tail>
-auto first(const T& value, const Tail&...) -> const T& {
+constexpr auto first(const T& value, const Tail&...) -> const T& {
   return value;
 }
 
@@ -436,8 +436,8 @@ FMT_BEGIN_EXPORT
 template <typename CompiledFormat, typename... Args,
           typename Char = typename CompiledFormat::char_type,
           FMT_ENABLE_IF(detail::is_compiled_format<CompiledFormat>::value)>
-FMT_INLINE std::basic_string<Char> format(const CompiledFormat& cf,
-                                          const Args&... args) {
+FMT_INLINE FMT_CONSTEXPR_STRING std::basic_string<Char> format(
+    const CompiledFormat& cf, const Args&... args) {
   auto s = std::basic_string<Char>();
   cf.format(std::back_inserter(s), args...);
   return s;
@@ -452,8 +452,8 @@ constexpr FMT_INLINE OutputIt format_to(OutputIt out, const CompiledFormat& cf,
 
 template <typename S, typename... Args,
           FMT_ENABLE_IF(is_compiled_string<S>::value)>
-FMT_INLINE std::basic_string<typename S::char_type> format(const S&,
-                                                           Args&&... args) {
+FMT_INLINE FMT_CONSTEXPR_STRING std::basic_string<typename S::char_type> format(
+    const S&, Args&&... args) {
   if constexpr (std::is_same<typename S::char_type, char>::value) {
     constexpr auto str = basic_string_view<typename S::char_type>(S());
     if constexpr (str.size() == 2 && str[0] == '{' && str[1] == '}') {
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/format-inl.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/format-inl.h
index a5b79dbe49..43596a0fe8 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/format-inl.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/format-inl.h
@@ -22,7 +22,7 @@
 
 #include "format.h"
 
-#if FMT_USE_LOCALE
+#if FMT_USE_LOCALE && !defined(FMT_MODULE)
 #  include <locale>
 #endif
 
@@ -212,7 +212,7 @@ inline auto floor_log10_pow2_minus_log10_4_over_3(int e) noexcept -> int {
   return (e * 631305 - 261663) >> 21;
 }
 
-FMT_INLINE_VARIABLE constexpr struct {
+FMT_INLINE_VARIABLE constexpr struct div_small_pow10_infos_struct {
   uint32_t divisor;
   int shift_amount;
 } div_small_pow10_infos[] = {{10, 16}, {100, 16}};
@@ -275,7 +275,7 @@ template <> struct cache_accessor<float> {
   static auto get_cached_power(int k) noexcept -> uint64_t {
     FMT_ASSERT(k >= float_info<float>::min_k && k <= float_info<float>::max_k,
                "k is out of range");
-    static constexpr const uint64_t pow10_significands[] = {
+    static constexpr uint64_t pow10_significands[] = {
         0x81ceb32c4b43fcf5, 0xa2425ff75e14fc32, 0xcad2f7f5359a3b3f,
         0xfd87b5f28300ca0e, 0x9e74d1b791e07e49, 0xc612062576589ddb,
         0xf79687aed3eec552, 0x9abe14cd44753b53, 0xc16d9a0095928a28,
@@ -370,7 +370,7 @@ template <> struct cache_accessor<double> {
     FMT_ASSERT(k >= float_info<double>::min_k && k <= float_info<double>::max_k,
                "k is out of range");
 
-    static constexpr const uint128_fallback pow10_significands[] = {
+    static constexpr uint128_fallback pow10_significands[] = {
 #if FMT_USE_FULL_CACHE_DRAGONBOX
       {0xff77b1fcbebcdc4f, 0x25e8e89c13bb0f7b},
       {0x9faacf3df73609b1, 0x77b191618c54e9ad},
@@ -1037,7 +1037,7 @@ template <> struct cache_accessor<double> {
 #if FMT_USE_FULL_CACHE_DRAGONBOX
     return pow10_significands[k - float_info<double>::min_k];
 #else
-    static constexpr const uint64_t powers_of_5_64[] = {
+    static constexpr uint64_t powers_of_5_64[] = {
         0x0000000000000001, 0x0000000000000005, 0x0000000000000019,
         0x000000000000007d, 0x0000000000000271, 0x0000000000000c35,
         0x0000000000003d09, 0x000000000001312d, 0x000000000005f5e1,
@@ -1097,7 +1097,7 @@ template <> struct cache_accessor<double> {
     return {r.high(), r.low() == 0};
   }
 
-  static auto compute_delta(cache_entry_type const& cache, int beta) noexcept
+  static auto compute_delta(const cache_entry_type& cache, int beta) noexcept
       -> uint32_t {
     return static_cast<uint32_t>(cache.high() >> (64 - 1 - beta));
   }
@@ -1526,9 +1526,8 @@ template <typename F> class glibc_file : public file_base<F> {
   }
 
   void init_buffer() {
-    if (this->file_->_IO_write_ptr) return;
+    if (this->file_->_IO_write_ptr < this->file_->_IO_write_end) return;
     // Force buffer initialization by placing and removing a char in a buffer.
-    assume(this->file_->_IO_write_ptr >= this->file_->_IO_write_end);
     putc_unlocked(0, this->file_);
     --this->file_->_IO_write_ptr;
   }
@@ -1550,7 +1549,8 @@ template <typename F> class glibc_file : public file_base<F> {
   bool needs_flush() const {
     if ((this->file_->_flags & line_buffered) == 0) return false;
     char* end = this->file_->_IO_write_end;
-    return memchr(end, '\n', to_unsigned(this->file_->_IO_write_ptr - end));
+    auto size = max_of<ptrdiff_t>(this->file_->_IO_write_ptr - end, 0);
+    return memchr(end, '\n', static_cast<size_t>(size));
   }
 
   void flush() { fflush_unlocked(this->file_); }
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/format.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/format.h
index 287e71631e..08b11a6ecb 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/format.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/format.h
@@ -44,6 +44,7 @@
 #  include <cmath>    // std::signbit
 #  include <cstddef>  // std::byte
 #  include <cstdint>  // uint32_t
+#  include <cstdlib>  // std::malloc, std::free
 #  include <cstring>  // std::memcpy
 #  include <limits>   // std::numeric_limits
 #  include <new>      // std::bad_alloc
@@ -117,6 +118,34 @@
 #  define FMT_NOINLINE
 #endif
 
+// Detect constexpr std::string.
+#if !FMT_USE_CONSTEVAL
+#  define FMT_USE_CONSTEXPR_STRING 0
+#elif defined(__cpp_lib_constexpr_string) && \
+    __cpp_lib_constexpr_string >= 201907L
+#  if FMT_CLANG_VERSION && FMT_GLIBCXX_RELEASE
+// clang + libstdc++ are able to work only starting with gcc13.3
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113294
+#    if FMT_GLIBCXX_RELEASE < 13
+#      define FMT_USE_CONSTEXPR_STRING 0
+#    elif FMT_GLIBCXX_RELEASE == 13 && __GLIBCXX__ < 20240521
+#      define FMT_USE_CONSTEXPR_STRING 0
+#    else
+#      define FMT_USE_CONSTEXPR_STRING 1
+#    endif
+#  else
+#    define FMT_USE_CONSTEXPR_STRING 1
+#  endif
+#else
+#  define FMT_USE_CONSTEXPR_STRING 0
+#endif
+#if FMT_USE_CONSTEXPR_STRING
+#  define FMT_CONSTEXPR_STRING constexpr
+#else
+#  define FMT_CONSTEXPR_STRING
+#endif
+
+// GCC 4.9 doesn't support qualified names in specializations.
 namespace std {
 template <typename T> struct iterator_traits<fmt::basic_appender<T>> {
   using iterator_category = output_iterator_tag;
@@ -525,6 +554,8 @@ FMT_CONSTEXPR auto fill_n(OutputIt out, Size count, const T& value)
 template <typename T, typename Size>
 FMT_CONSTEXPR20 auto fill_n(T* out, Size count, char value) -> T* {
   if (is_constant_evaluated()) return fill_n<T*, Size, T>(out, count, value);
+  static_assert(sizeof(T) == 1,
+                "sizeof(T) must be 1 to use char for initialization");
   std::memset(out, value, to_unsigned(count));
   return out + count;
 }
@@ -554,10 +585,10 @@ FMT_CONSTEXPR FMT_NOINLINE auto copy_noinline(InputIt begin, InputIt end,
  */
 FMT_CONSTEXPR inline auto utf8_decode(const char* s, uint32_t* c, int* e)
     -> const char* {
-  constexpr const int masks[] = {0x00, 0x7f, 0x1f, 0x0f, 0x07};
-  constexpr const uint32_t mins[] = {4194304, 0, 128, 2048, 65536};
-  constexpr const int shiftc[] = {0, 18, 12, 6, 0};
-  constexpr const int shifte[] = {0, 6, 4, 2, 0};
+  constexpr int masks[] = {0x00, 0x7f, 0x1f, 0x0f, 0x07};
+  constexpr uint32_t mins[] = {4194304, 0, 128, 2048, 65536};
+  constexpr int shiftc[] = {0, 18, 12, 6, 0};
+  constexpr int shifte[] = {0, 6, 4, 2, 0};
 
   int len = "\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\0\0\0\0\0\0\0\0\2\2\2\2\3\3\4"
       [static_cast<unsigned char>(*s) >> 3];
@@ -628,21 +659,9 @@ FMT_CONSTEXPR void for_each_codepoint(string_view s, F f) {
   } while (buf_ptr < buf + num_chars_left);
 }
 
-template <typename Char>
-inline auto compute_width(basic_string_view<Char> s) -> size_t {
-  return s.size();
-}
-
-// Computes approximate display width of a UTF-8 string.
-FMT_CONSTEXPR inline auto compute_width(string_view s) -> size_t {
-  size_t num_code_points = 0;
-  // It is not a lambda for compatibility with C++14.
-  struct count_code_points {
-    size_t* count;
-    FMT_CONSTEXPR auto operator()(uint32_t cp, string_view) const -> bool {
-      *count += to_unsigned(
-          1 +
-          (cp >= 0x1100 &&
+FMT_CONSTEXPR inline auto display_width_of(uint32_t cp) noexcept -> size_t {
+  return to_unsigned(
+      1 + (cp >= 0x1100 &&
            (cp <= 0x115f ||  // Hangul Jamo init. consonants
             cp == 0x2329 ||  // LEFT-POINTING ANGLE BRACKET
             cp == 0x232a ||  // RIGHT-POINTING ANGLE BRACKET
@@ -660,32 +679,6 @@ FMT_CONSTEXPR inline auto compute_width(string_view s) -> size_t {
             (cp >= 0x1f300 && cp <= 0x1f64f) ||
             // Supplemental Symbols and Pictographs:
             (cp >= 0x1f900 && cp <= 0x1f9ff))));
-      return true;
-    }
-  };
-  // We could avoid branches by using utf8_decode directly.
-  for_each_codepoint(s, count_code_points{&num_code_points});
-  return num_code_points;
-}
-
-template <typename Char>
-inline auto code_point_index(basic_string_view<Char> s, size_t n) -> size_t {
-  return min_of(n, s.size());
-}
-
-// Calculates the index of the nth code point in a UTF-8 string.
-inline auto code_point_index(string_view s, size_t n) -> size_t {
-  size_t result = s.size();
-  const char* begin = s.begin();
-  for_each_codepoint(s, [begin, &n, &result](uint32_t, string_view sv) {
-    if (n != 0) {
-      --n;
-      return true;
-    }
-    result = to_unsigned(sv.begin() - begin);
-    return false;
-  });
-  return result;
 }
 
 template <typename T> struct is_integral : std::is_integral<T> {};
@@ -705,7 +698,7 @@ using is_integer =
 
 #if defined(FMT_USE_FLOAT128)
 // Use the provided definition.
-#elif FMT_CLANG_VERSION && FMT_HAS_INCLUDE(<quadmath.h>)
+#elif FMT_CLANG_VERSION >= 309 && FMT_HAS_INCLUDE(<quadmath.h>)
 #  define FMT_USE_FLOAT128 1
 #elif FMT_GCC_VERSION && defined(_GLIBCXX_USE_FLOAT128) && \
     !defined(__STRICT_ANSI__)
@@ -721,15 +714,17 @@ struct float128 {};
 
 template <typename T> using is_float128 = std::is_same<T, float128>;
 
-template <typename T>
-using is_floating_point =
-    bool_constant<std::is_floating_point<T>::value || is_float128<T>::value>;
+template <typename T> struct is_floating_point : std::is_floating_point<T> {};
+template <> struct is_floating_point<float128> : std::true_type {};
 
-template <typename T, bool = std::is_floating_point<T>::value>
+template <typename T, bool = is_floating_point<T>::value>
 struct is_fast_float : bool_constant<std::numeric_limits<T>::is_iec559 &&
                                      sizeof(T) <= sizeof(double)> {};
 template <typename T> struct is_fast_float<T, false> : std::false_type {};
 
+template <typename T>
+using fast_float_t = conditional_t<sizeof(T) == sizeof(double), double, float>;
+
 template <typename T>
 using is_double_double = bool_constant<std::numeric_limits<T>::digits == 106>;
 
@@ -738,18 +733,19 @@ using is_double_double = bool_constant<std::numeric_limits<T>::digits == 106>;
 #endif
 
 // An allocator that uses malloc/free to allow removing dependency on the C++
-// standard libary runtime.
-template <typename T> struct allocator {
+// standard libary runtime. std::decay is used for back_inserter to be found by
+// ADL when applied to memory_buffer.
+template <typename T> struct allocator : private std::decay<void> {
   using value_type = T;
 
   T* allocate(size_t n) {
     FMT_ASSERT(n <= max_value<size_t>() / sizeof(T), "");
-    T* p = static_cast<T*>(malloc(n * sizeof(T)));
+    T* p = static_cast<T*>(std::malloc(n * sizeof(T)));
     if (!p) FMT_THROW(std::bad_alloc());
     return p;
   }
 
-  void deallocate(T* p, size_t) { free(p); }
+  void deallocate(T* p, size_t) { std::free(p); }
 };
 
 }  // namespace detail
@@ -1044,7 +1040,7 @@ inline auto do_count_digits(uint64_t n) -> int {
       10, 11, 11, 11, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 15, 15,
       15, 16, 16, 16, 16, 17, 17, 17, 18, 18, 18, 19, 19, 19, 19, 20};
   auto t = bsr2log10[FMT_BUILTIN_CLZLL(n | 1) ^ 63];
-  static constexpr const uint64_t zero_or_powers_of_10[] = {
+  static constexpr uint64_t zero_or_powers_of_10[] = {
       0, 0, FMT_POWERS_OF_10(1U), FMT_POWERS_OF_10(1000000000ULL),
       10000000000000000000ULL};
   return t - (n < zero_or_powers_of_10[t]);
@@ -1225,7 +1221,7 @@ FMT_CONSTEXPR auto do_format_base2e(int base_bits, Char* out, UInt value,
   out += size;
   do {
     const char* digits = upper ? "0123456789ABCDEF" : "0123456789abcdef";
-    unsigned digit = static_cast<unsigned>(value & ((1 << base_bits) - 1));
+    unsigned digit = static_cast<unsigned>(value & ((1u << base_bits) - 1));
     *--out = static_cast<Char>(base_bits < 4 ? static_cast<char>('0' + digit)
                                              : digits[digit]);
   } while ((value >>= base_bits) != 0);
@@ -1487,6 +1483,13 @@ template <typename Float> constexpr auto exponent_bias() -> int {
                               : std::numeric_limits<Float>::max_exponent - 1;
 }
 
+FMT_CONSTEXPR inline auto compute_exp_size(int exp) -> int {
+  auto prefix_size = 2;  // sign + 'e'
+  auto abs_exp = exp >= 0 ? exp : -exp;
+  if (exp < 100) return prefix_size + 2;
+  return prefix_size + (abs_exp >= 1000 ? 4 : 3);
+}
+
 // Writes the exponent exp in the form "[+-]d{2,3}" to buffer.
 template <typename Char, typename OutputIt>
 FMT_CONSTEXPR auto write_exponent(int exp, OutputIt out) -> OutputIt {
@@ -1519,7 +1522,7 @@ template <typename F> struct basic_fp {
   F f;
   int e;
 
-  static constexpr const int num_significand_bits =
+  static constexpr int num_significand_bits =
       static_cast<int>(sizeof(F) * num_bits<unsigned char>());
 
   constexpr basic_fp() : f(0), e(0) {}
@@ -1613,7 +1616,7 @@ constexpr auto convert_float(T value) -> convert_float_result<T> {
 }
 
 template <typename Char, typename OutputIt>
-FMT_NOINLINE FMT_CONSTEXPR auto fill(OutputIt it, size_t n,
+FMT_CONSTEXPR FMT_NOINLINE auto fill(OutputIt it, size_t n,
                                      const basic_specs& specs) -> OutputIt {
   auto fill_size = specs.fill_size();
   if (fill_size == 1) return detail::fill_n(it, n, specs.fill_unit<Char>());
@@ -1964,8 +1967,7 @@ FMT_CONSTEXPR auto make_write_int_arg(T value, sign s)
     prefix = 0x01000000 | '-';
     abs_value = 0 - abs_value;
   } else {
-    constexpr const unsigned prefixes[4] = {0, 0, 0x1000000u | '+',
-                                            0x1000000u | ' '};
+    constexpr unsigned prefixes[4] = {0, 0, 0x1000000u | '+', 0x1000000u | ' '};
     prefix = prefixes[static_cast<int>(s)];
   }
   return {abs_value, prefix};
@@ -2018,7 +2020,7 @@ FMT_CONSTEXPR FMT_INLINE auto write_int(OutputIt out, write_int_arg<T> arg,
                                         const format_specs& specs) -> OutputIt {
   static_assert(std::is_same<T, uint32_or_64_or_128_t<T>>::value, "");
 
-  constexpr int buffer_size = num_bits<T>();
+  constexpr size_t buffer_size = num_bits<T>();
   char buffer[buffer_size];
   if (is_constant_evaluated()) fill_n(buffer, buffer_size, '\0');
   const char* begin = nullptr;
@@ -2110,13 +2112,98 @@ FMT_CONSTEXPR FMT_INLINE auto write(OutputIt out, T value,
   return write_int<Char>(out, make_write_int_arg(value, specs.sign()), specs);
 }
 
-template <typename Char, typename OutputIt>
+template <typename Char, typename OutputIt,
+          FMT_ENABLE_IF(std::is_same<Char, char>::value)>
+FMT_CONSTEXPR auto write(OutputIt out, basic_string_view<Char> s,
+                         const format_specs& specs) -> OutputIt {
+  bool is_debug = specs.type() == presentation_type::debug;
+  if (specs.precision < 0 && specs.width == 0) {
+    auto&& it = reserve(out, s.size());
+    return is_debug ? write_escaped_string(it, s) : copy<char>(s, it);
+  }
+
+  size_t display_width_limit =
+      specs.precision < 0 ? SIZE_MAX : to_unsigned(specs.precision);
+  size_t display_width =
+      !is_debug || specs.precision == 0 ? 0 : 1;  // Account for opening "
+  size_t size = !is_debug || specs.precision == 0 ? 0 : 1;
+  for_each_codepoint(s, [&](uint32_t cp, string_view sv) {
+    if (is_debug && needs_escape(cp)) {
+      counting_buffer<char> buf;
+      write_escaped_cp(basic_appender<char>(buf),
+                       find_escape_result<char>{sv.begin(), sv.end(), cp});
+      // We're reinterpreting bytes as display width. That's okay
+      // because write_escaped_cp() only writes ASCII characters.
+      size_t cp_width = buf.count();
+      if (display_width + cp_width <= display_width_limit) {
+        display_width += cp_width;
+        size += cp_width;
+        // If this is the end of the string, account for closing "
+        if (display_width < display_width_limit && sv.end() == s.end()) {
+          ++display_width;
+          ++size;
+        }
+        return true;
+      }
+
+      size += display_width_limit - display_width;
+      display_width = display_width_limit;
+      return false;
+    }
+
+    size_t cp_width = display_width_of(cp);
+    if (cp_width + display_width <= display_width_limit) {
+      display_width += cp_width;
+      size += sv.size();
+      // If this is the end of the string, account for closing "
+      if (is_debug && display_width < display_width_limit &&
+          sv.end() == s.end()) {
+        ++display_width;
+        ++size;
+      }
+      return true;
+    }
+
+    return false;
+  });
+
+  struct bounded_output_iterator {
+    reserve_iterator<OutputIt> underlying_iterator;
+    size_t bound;
+
+    FMT_CONSTEXPR auto operator*() -> bounded_output_iterator& { return *this; }
+    FMT_CONSTEXPR auto operator++() -> bounded_output_iterator& {
+      return *this;
+    }
+    FMT_CONSTEXPR auto operator++(int) -> bounded_output_iterator& {
+      return *this;
+    }
+    FMT_CONSTEXPR auto operator=(char c) -> bounded_output_iterator& {
+      if (bound > 0) {
+        *underlying_iterator++ = c;
+        --bound;
+      }
+      return *this;
+    }
+  };
+
+  return write_padded<char>(
+      out, specs, size, display_width, [&](reserve_iterator<OutputIt> it) {
+        return is_debug
+                   ? write_escaped_string(bounded_output_iterator{it, size}, s)
+                         .underlying_iterator
+                   : copy<char>(s.data(), s.data() + size, it);
+      });
+}
+
+template <typename Char, typename OutputIt,
+          FMT_ENABLE_IF(!std::is_same<Char, char>::value)>
 FMT_CONSTEXPR auto write(OutputIt out, basic_string_view<Char> s,
                          const format_specs& specs) -> OutputIt {
   auto data = s.data();
   auto size = s.size();
   if (specs.precision >= 0 && to_unsigned(specs.precision) < size)
-    size = code_point_index(s, to_unsigned(specs.precision));
+    size = to_unsigned(specs.precision);
 
   bool is_debug = specs.type() == presentation_type::debug;
   if (is_debug) {
@@ -2125,22 +2212,19 @@ FMT_CONSTEXPR auto write(OutputIt out, basic_string_view<Char> s,
     size = buf.count();
   }
 
-  size_t width = 0;
-  if (specs.width != 0) {
-    width =
-        is_debug ? size : compute_width(basic_string_view<Char>(data, size));
-  }
   return write_padded<Char>(
-      out, specs, size, width, [=](reserve_iterator<OutputIt> it) {
+      out, specs, size, [&](reserve_iterator<OutputIt> it) {
         return is_debug ? write_escaped_string(it, s)
                         : copy<Char>(data, data + size, it);
       });
 }
+
 template <typename Char, typename OutputIt>
 FMT_CONSTEXPR auto write(OutputIt out, basic_string_view<Char> s,
                          const format_specs& specs, locale_ref) -> OutputIt {
   return write<Char>(out, s, specs);
 }
+
 template <typename Char, typename OutputIt>
 FMT_CONSTEXPR auto write(OutputIt out, const Char* s, const format_specs& specs,
                          locale_ref) -> OutputIt {
@@ -2274,7 +2358,7 @@ inline auto write_significand(Char* out, UInt significand, int significand_size,
   int floating_size = significand_size - integral_size;
   for (int i = floating_size / 2; i > 0; --i) {
     out -= 2;
-    write2digits(out, static_cast<std::size_t>(significand % 100));
+    write2digits(out, static_cast<size_t>(significand % 100));
     significand /= 100;
   }
   if (floating_size % 2 != 0) {
@@ -2328,110 +2412,18 @@ FMT_CONSTEXPR20 auto write_significand(OutputIt out, T significand,
                                      buffer.end(), out);
 }
 
-template <typename Char, typename OutputIt, typename DecimalFP,
-          typename Grouping = digit_grouping<Char>>
-FMT_CONSTEXPR20 auto do_write_float(OutputIt out, const DecimalFP& f,
-                                    const format_specs& specs, sign s,
-                                    int exp_upper, locale_ref loc) -> OutputIt {
-  auto significand = f.significand;
-  int significand_size = get_significand_size(f);
-  const Char zero = static_cast<Char>('0');
-  size_t size = to_unsigned(significand_size) + (s != sign::none ? 1 : 0);
-  using iterator = reserve_iterator<OutputIt>;
+// Numbers with exponents greater or equal to the returned value will use
+// the exponential notation.
+template <typename T> FMT_CONSTEVAL auto exp_upper() -> int {
+  return std::numeric_limits<T>::digits10 != 0
+             ? min_of(16, std::numeric_limits<T>::digits10 + 1)
+             : 16;
+}
 
-  Char decimal_point = specs.localized() ? detail::decimal_point<Char>(loc)
-                                         : static_cast<Char>('.');
-
-  int output_exp = f.exponent + significand_size - 1;
-  auto use_exp_format = [=]() {
-    if (specs.type() == presentation_type::exp) return true;
-    if (specs.type() == presentation_type::fixed) return false;
-    // Use the fixed notation if the exponent is in [exp_lower, exp_upper),
-    // e.g. 0.0001 instead of 1e-04. Otherwise use the exponent notation.
-    const int exp_lower = -4;
-    return output_exp < exp_lower ||
-           output_exp >= (specs.precision > 0 ? specs.precision : exp_upper);
-  };
-  if (use_exp_format()) {
-    int num_zeros = 0;
-    if (specs.alt()) {
-      num_zeros = specs.precision - significand_size;
-      if (num_zeros < 0) num_zeros = 0;
-      size += to_unsigned(num_zeros);
-    } else if (significand_size == 1) {
-      decimal_point = Char();
-    }
-    auto abs_output_exp = output_exp >= 0 ? output_exp : -output_exp;
-    int exp_digits = 2;
-    if (abs_output_exp >= 100) exp_digits = abs_output_exp >= 1000 ? 4 : 3;
-
-    size += to_unsigned((decimal_point ? 1 : 0) + 2 + exp_digits);
-    char exp_char = specs.upper() ? 'E' : 'e';
-    auto write = [=](iterator it) {
-      if (s != sign::none) *it++ = detail::getsign<Char>(s);
-      // Insert a decimal point after the first digit and add an exponent.
-      it = write_significand(it, significand, significand_size, 1,
-                             decimal_point);
-      if (num_zeros > 0) it = detail::fill_n(it, num_zeros, zero);
-      *it++ = static_cast<Char>(exp_char);
-      return write_exponent<Char>(output_exp, it);
-    };
-    return specs.width > 0
-               ? write_padded<Char, align::right>(out, specs, size, write)
-               : base_iterator(out, write(reserve(out, size)));
-  }
-
-  int exp = f.exponent + significand_size;
-  if (f.exponent >= 0) {
-    // 1234e5 -> 123400000[.0+]
-    size += to_unsigned(f.exponent);
-    int num_zeros = specs.precision - exp;
-    abort_fuzzing_if(num_zeros > 5000);
-    if (specs.alt()) {
-      ++size;
-      if (num_zeros <= 0 && specs.type() != presentation_type::fixed)
-        num_zeros = 0;
-      if (num_zeros > 0) size += to_unsigned(num_zeros);
-    }
-    auto grouping = Grouping(loc, specs.localized());
-    size += to_unsigned(grouping.count_separators(exp));
-    return write_padded<Char, align::right>(out, specs, size, [&](iterator it) {
-      if (s != sign::none) *it++ = detail::getsign<Char>(s);
-      it = write_significand<Char>(it, significand, significand_size,
-                                   f.exponent, grouping);
-      if (!specs.alt()) return it;
-      *it++ = decimal_point;
-      return num_zeros > 0 ? detail::fill_n(it, num_zeros, zero) : it;
-    });
-  } else if (exp > 0) {
-    // 1234e-2 -> 12.34[0+]
-    int num_zeros = specs.alt() ? specs.precision - significand_size : 0;
-    size += 1 + static_cast<unsigned>(max_of(num_zeros, 0));
-    auto grouping = Grouping(loc, specs.localized());
-    size += to_unsigned(grouping.count_separators(exp));
-    return write_padded<Char, align::right>(out, specs, size, [&](iterator it) {
-      if (s != sign::none) *it++ = detail::getsign<Char>(s);
-      it = write_significand(it, significand, significand_size, exp,
-                             decimal_point, grouping);
-      return num_zeros > 0 ? detail::fill_n(it, num_zeros, zero) : it;
-    });
-  }
-  // 1234e-6 -> 0.001234
-  int num_zeros = -exp;
-  if (significand_size == 0 && specs.precision >= 0 &&
-      specs.precision < num_zeros) {
-    num_zeros = specs.precision;
-  }
-  bool pointy = num_zeros != 0 || significand_size != 0 || specs.alt();
-  size += 1 + (pointy ? 1 : 0) + to_unsigned(num_zeros);
-  return write_padded<Char, align::right>(out, specs, size, [&](iterator it) {
-    if (s != sign::none) *it++ = detail::getsign<Char>(s);
-    *it++ = zero;
-    if (!pointy) return it;
-    *it++ = decimal_point;
-    it = detail::fill_n(it, num_zeros, zero);
-    return write_significand<Char>(it, significand, significand_size);
-  });
+// Use the fixed notation if the exponent is in [-4, exp_upper),
+// e.g. 0.0001 instead of 1e-04. Otherwise use the exponent notation.
+constexpr auto use_fixed(int exp, int exp_upper) -> bool {
+  return exp >= -4 && exp < exp_upper;
 }
 
 template <typename Char> class fallback_digit_grouping {
@@ -2448,16 +2440,122 @@ template <typename Char> class fallback_digit_grouping {
   }
 };
 
+template <typename Char, typename Grouping, typename OutputIt,
+          typename DecimalFP>
+FMT_CONSTEXPR20 auto write_fixed(OutputIt out, const DecimalFP& f,
+                                 int significand_size, Char decimal_point,
+                                 const format_specs& specs, sign s,
+                                 locale_ref loc = {}) -> OutputIt {
+  using iterator = reserve_iterator<OutputIt>;
+
+  int exp = f.exponent + significand_size;
+  long long size = significand_size + (s != sign::none ? 1 : 0);
+  if (f.exponent >= 0) {
+    // 1234e5 -> 123400000[.0+]
+    size += f.exponent;
+    int num_zeros = specs.precision - exp;
+    abort_fuzzing_if(num_zeros > 5000);
+    if (specs.alt()) {
+      ++size;
+      if (num_zeros <= 0 && specs.type() != presentation_type::fixed)
+        num_zeros = 0;
+      if (num_zeros > 0) size += num_zeros;
+    }
+    auto grouping = Grouping(loc, specs.localized());
+    size += grouping.count_separators(exp);
+    return write_padded<Char, align::right>(
+        out, specs, to_unsigned(size), [&](iterator it) {
+          if (s != sign::none) *it++ = detail::getsign<Char>(s);
+          it = write_significand<Char>(it, f.significand, significand_size,
+                                       f.exponent, grouping);
+          if (!specs.alt()) return it;
+          *it++ = decimal_point;
+          return num_zeros > 0 ? detail::fill_n(it, num_zeros, Char('0')) : it;
+        });
+  }
+  if (exp > 0) {
+    // 1234e-2 -> 12.34[0+]
+    int num_zeros = specs.alt() ? specs.precision - significand_size : 0;
+    size += 1 + max_of(num_zeros, 0);
+    auto grouping = Grouping(loc, specs.localized());
+    size += grouping.count_separators(exp);
+    return write_padded<Char, align::right>(
+        out, specs, to_unsigned(size), [&](iterator it) {
+          if (s != sign::none) *it++ = detail::getsign<Char>(s);
+          it = write_significand(it, f.significand, significand_size, exp,
+                                 decimal_point, grouping);
+          return num_zeros > 0 ? detail::fill_n(it, num_zeros, Char('0')) : it;
+        });
+  }
+  // 1234e-6 -> 0.001234
+  int num_zeros = -exp;
+  if (significand_size == 0 && specs.precision >= 0 &&
+      specs.precision < num_zeros) {
+    num_zeros = specs.precision;
+  }
+  bool pointy = num_zeros != 0 || significand_size != 0 || specs.alt();
+  size += 1 + (pointy ? 1 : 0) + num_zeros;
+  return write_padded<Char, align::right>(
+      out, specs, to_unsigned(size), [&](iterator it) {
+        if (s != sign::none) *it++ = detail::getsign<Char>(s);
+        *it++ = Char('0');
+        if (!pointy) return it;
+        *it++ = decimal_point;
+        it = detail::fill_n(it, num_zeros, Char('0'));
+        return write_significand<Char>(it, f.significand, significand_size);
+      });
+}
+
+template <typename Char, typename Grouping, typename OutputIt,
+          typename DecimalFP>
+FMT_CONSTEXPR20 auto do_write_float(OutputIt out, const DecimalFP& f,
+                                    const format_specs& specs, sign s,
+                                    int exp_upper, locale_ref loc) -> OutputIt {
+  Char point = specs.localized() ? detail::decimal_point<Char>(loc) : Char('.');
+  int significand_size = get_significand_size(f);
+  int exp = f.exponent + significand_size - 1;
+  if (specs.type() == presentation_type::fixed ||
+      (specs.type() != presentation_type::exp &&
+       use_fixed(exp, specs.precision > 0 ? specs.precision : exp_upper))) {
+    return write_fixed<Char, Grouping>(out, f, significand_size, point, specs,
+                                       s, loc);
+  }
+
+  // Write value in the exponential format.
+  int num_zeros = 0;
+  long long size = significand_size + (s != sign::none ? 1 : 0);
+  if (specs.alt()) {
+    num_zeros = max_of(specs.precision - significand_size, 0);
+    size += num_zeros;
+  } else if (significand_size == 1) {
+    point = Char();
+  }
+  size += (point ? 1 : 0) + compute_exp_size(exp);
+  char exp_char = specs.upper() ? 'E' : 'e';
+  auto write = [=](reserve_iterator<OutputIt> it) {
+    if (s != sign::none) *it++ = detail::getsign<Char>(s);
+    // Insert a decimal point after the first digit and add an exponent.
+    it = write_significand(it, f.significand, significand_size, 1, point);
+    if (num_zeros > 0) it = detail::fill_n(it, num_zeros, Char('0'));
+    *it++ = Char(exp_char);
+    return write_exponent<Char>(exp, it);
+  };
+  auto usize = to_unsigned(size);
+  return specs.width > 0
+             ? write_padded<Char, align::right>(out, specs, usize, write)
+             : base_iterator(out, write(reserve(out, usize)));
+}
+
 template <typename Char, typename OutputIt, typename DecimalFP>
 FMT_CONSTEXPR20 auto write_float(OutputIt out, const DecimalFP& f,
                                  const format_specs& specs, sign s,
                                  int exp_upper, locale_ref loc) -> OutputIt {
   if (is_constant_evaluated()) {
-    return do_write_float<Char, OutputIt, DecimalFP,
-                          fallback_digit_grouping<Char>>(out, f, specs, s,
-                                                         exp_upper, loc);
+    return do_write_float<Char, fallback_digit_grouping<Char>>(out, f, specs, s,
+                                                               exp_upper, loc);
   } else {
-    return do_write_float<Char>(out, f, specs, s, exp_upper, loc);
+    return do_write_float<Char, digit_grouping<Char>>(out, f, specs, s,
+                                                      exp_upper, loc);
   }
 }
 
@@ -2472,8 +2570,8 @@ template <typename T>
 struct has_isfinite<T, enable_if_t<sizeof(std::isfinite(T())) != 0>>
     : std::true_type {};
 
-template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value&&
-                                        has_isfinite<T>::value)>
+template <typename T,
+          FMT_ENABLE_IF(is_floating_point<T>::value&& has_isfinite<T>::value)>
 FMT_CONSTEXPR20 auto isfinite(T value) -> bool {
   constexpr T inf = T(std::numeric_limits<double>::infinity());
   if (is_constant_evaluated())
@@ -2728,7 +2826,7 @@ class bigint {
     bigits_.resize(to_unsigned(num_bigits + exp_difference));
     for (int i = num_bigits - 1, j = i + exp_difference; i >= 0; --i, --j)
       bigits_[j] = bigits_[i];
-    memset(bigits_.data(), 0, to_unsigned(exp_difference) * sizeof(bigit));
+    fill_n(bigits_.data(), to_unsigned(exp_difference), 0U);
     exp_ -= exp_difference;
   }
 
@@ -3289,17 +3387,12 @@ FMT_CONSTEXPR20 auto format_float(Float value, int precision,
   return exp;
 }
 
-// Numbers with exponents greater or equal to the returned value will use
-// the exponential notation.
-template <typename T> constexpr auto exp_upper() -> int {
-  return std::numeric_limits<T>::digits10 != 0
-             ? min_of(16, std::numeric_limits<T>::digits10 + 1)
-             : 16;
-}
+template <typename Char, typename OutputIt, typename T,
+          FMT_ENABLE_IF(is_floating_point<T>::value)>
+FMT_CONSTEXPR20 auto write(OutputIt out, T value, format_specs specs,
+                           locale_ref loc = {}) -> OutputIt {
+  if (specs.localized() && write_loc(out, value, specs, loc)) return out;
 
-template <typename Char, typename OutputIt, typename T>
-FMT_CONSTEXPR20 auto write_float(OutputIt out, T value, format_specs specs,
-                                 locale_ref loc) -> OutputIt {
   // Use signbit because value < 0 is false for NaN.
   sign s = detail::signbit(value) ? sign::minus : specs.sign();
 
@@ -3312,15 +3405,14 @@ FMT_CONSTEXPR20 auto write_float(OutputIt out, T value, format_specs specs,
     if (specs.width != 0) --specs.width;
   }
 
-  constexpr int exp_upper = detail::exp_upper<T>();
+  const int exp_upper = detail::exp_upper<T>();
   int precision = specs.precision;
   if (precision < 0) {
     if (specs.type() != presentation_type::none) {
       precision = 6;
     } else if (is_fast_float<T>::value && !is_constant_evaluated()) {
       // Use Dragonbox for the shortest format.
-      using floaty = conditional_t<sizeof(T) >= sizeof(double), double, float>;
-      auto dec = dragonbox::to_decimal(static_cast<floaty>(value));
+      auto dec = dragonbox::to_decimal(static_cast<fast_float_t<T>>(value));
       return write_float<Char>(out, dec, specs, s, exp_upper, loc);
     }
   }
@@ -3352,38 +3444,44 @@ FMT_CONSTEXPR20 auto write_float(OutputIt out, T value, format_specs specs,
   return write_float<Char>(out, f, specs, s, exp_upper, loc);
 }
 
-template <typename Char, typename OutputIt, typename T,
-          FMT_ENABLE_IF(is_floating_point<T>::value)>
-FMT_CONSTEXPR20 auto write(OutputIt out, T value, format_specs specs,
-                           locale_ref loc = {}) -> OutputIt {
-  return specs.localized() && write_loc(out, value, specs, loc)
-             ? out
-             : write_float<Char>(out, value, specs, loc);
-}
-
 template <typename Char, typename OutputIt, typename T,
           FMT_ENABLE_IF(is_fast_float<T>::value)>
 FMT_CONSTEXPR20 auto write(OutputIt out, T value) -> OutputIt {
   if (is_constant_evaluated()) return write<Char>(out, value, format_specs());
 
   auto s = detail::signbit(value) ? sign::minus : sign::none;
+  auto mask = exponent_mask<fast_float_t<T>>();
+  if ((bit_cast<decltype(mask)>(value) & mask) == mask)
+    return write_nonfinite<Char>(out, std::isnan(value), {}, s);
 
-  constexpr auto specs = format_specs();
-  using floaty = conditional_t<sizeof(T) >= sizeof(double), double, float>;
-  using floaty_uint = typename dragonbox::float_info<floaty>::carrier_uint;
-  floaty_uint mask = exponent_mask<floaty>();
-  if ((bit_cast<floaty_uint>(value) & mask) == mask)
-    return write_nonfinite<Char>(out, std::isnan(value), specs, s);
+  auto dec = dragonbox::to_decimal(static_cast<fast_float_t<T>>(value));
+  int significand_size = count_digits(dec.significand);
+  int exp = dec.exponent + significand_size - 1;
+  if (use_fixed(exp, detail::exp_upper<T>())) {
+    return write_fixed<Char, fallback_digit_grouping<Char>>(
+        out, dec, significand_size, Char('.'), {}, s);
+  }
 
-  auto dec = dragonbox::to_decimal(static_cast<floaty>(value));
-  return write_float<Char>(out, dec, specs, s, exp_upper<T>(), {});
+  // Write value in the exponential format.
+  auto has_decimal_point = significand_size != 1;
+  size_t size =
+      to_unsigned((s != sign::none ? 1 : 0) + significand_size +
+                  (has_decimal_point ? 1 : 0) + compute_exp_size(exp));
+  auto it = reserve(out, size);
+  if (s != sign::none) *it++ = Char('-');
+  // Insert a decimal point after the first digit and add an exponent.
+  it = write_significand(it, dec.significand, significand_size, 1,
+                         has_decimal_point ? Char('.') : Char());
+  *it++ = Char('e');
+  it = write_exponent<Char>(exp, it);
+  return base_iterator(out, it);
 }
 
 template <typename Char, typename OutputIt, typename T,
           FMT_ENABLE_IF(is_floating_point<T>::value &&
                         !is_fast_float<T>::value)>
 inline auto write(OutputIt out, T value) -> OutputIt {
-  return write<Char>(out, value, format_specs());
+  return write<Char>(out, value, {});
 }
 
 template <typename Char, typename OutputIt>
@@ -3825,7 +3923,7 @@ struct formatter<T, Char, void_t<detail::format_as_result<T>>>
  *     auto s = fmt::format("{}", fmt::ptr(p));
  */
 template <typename T> auto ptr(T p) -> const void* {
-  static_assert(std::is_pointer<T>::value, "");
+  static_assert(std::is_pointer<T>::value, "fmt::ptr used with non-pointer");
   return detail::bit_cast<const void*>(p);
 }
 
@@ -3850,13 +3948,14 @@ constexpr auto format_as(Enum e) noexcept -> underlying_t<Enum> {
 }  // namespace enums
 
 #ifdef __cpp_lib_byte
-template <> struct formatter<std::byte> : formatter<unsigned> {
+template <typename Char>
+struct formatter<std::byte, Char> : formatter<unsigned, Char> {
   static auto format_as(std::byte b) -> unsigned char {
     return static_cast<unsigned char>(b);
   }
   template <typename Context>
   auto format(std::byte b, Context& ctx) const -> decltype(ctx.out()) {
-    return formatter<unsigned>::format(format_as(b), ctx);
+    return formatter<unsigned, Char>::format(format_as(b), ctx);
   }
 };
 #endif
@@ -4208,7 +4307,7 @@ FMT_NODISCARD FMT_INLINE auto format(format_string<T...> fmt, T&&... args)
  *     std::string answer = fmt::to_string(42);
  */
 template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
-FMT_NODISCARD auto to_string(T value) -> std::string {
+FMT_NODISCARD FMT_CONSTEXPR_STRING auto to_string(T value) -> std::string {
   // The buffer should be large enough to store the number including the sign
   // or "false" for bool.
   char buffer[max_of(detail::digits10<T>() + 2, 5)];
@@ -4216,13 +4315,15 @@ FMT_NODISCARD auto to_string(T value) -> std::string {
 }
 
 template <typename T, FMT_ENABLE_IF(detail::use_format_as<T>::value)>
-FMT_NODISCARD auto to_string(const T& value) -> std::string {
+FMT_NODISCARD FMT_CONSTEXPR_STRING auto to_string(const T& value)
+    -> std::string {
   return to_string(format_as(value));
 }
 
 template <typename T, FMT_ENABLE_IF(!std::is_integral<T>::value &&
                                     !detail::use_format_as<T>::value)>
-FMT_NODISCARD auto to_string(const T& value) -> std::string {
+FMT_NODISCARD FMT_CONSTEXPR_STRING auto to_string(const T& value)
+    -> std::string {
   auto buffer = memory_buffer();
   detail::write<char>(appender(buffer), value);
   return {buffer.data(), buffer.size()};
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/ostream.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/ostream.h
index 71fd6c887e..bf2371b799 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/ostream.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/ostream.h
@@ -33,8 +33,8 @@
 FMT_BEGIN_NAMESPACE
 namespace detail {
 
-// Generate a unique explicit instantion in every translation unit using a tag
-// type in an anonymous namespace.
+// Generate a unique explicit instantiation in every translation unit using a
+// tag type in an anonymous namespace.
 namespace {
 struct file_access_tag {};
 }  // namespace
@@ -158,7 +158,8 @@ void print(std::ostream& os, format_string<T...> fmt, T&&... args) {
 
 FMT_EXPORT template <typename... T>
 void println(std::ostream& os, format_string<T...> fmt, T&&... args) {
-  fmt::print(os, "{}\n", fmt::format(fmt, std::forward<T>(args)...));
+  fmt::print(os, FMT_STRING("{}\n"),
+             fmt::format(fmt, std::forward<T>(args)...));
 }
 
 FMT_END_NAMESPACE
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/ranges.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/ranges.h
index 77d645f8e1..24c61e93b7 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/ranges.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/ranges.h
@@ -11,7 +11,6 @@
 #ifndef FMT_MODULE
 #  include <initializer_list>
 #  include <iterator>
-#  include <string>
 #  include <tuple>
 #  include <type_traits>
 #  include <utility>
@@ -31,7 +30,7 @@ template <typename T> class is_map {
   template <typename> static void check(...);
 
  public:
-  static constexpr const bool value =
+  static constexpr bool value =
       !std::is_void<decltype(check<T>(nullptr))>::value;
 };
 
@@ -40,17 +39,16 @@ template <typename T> class is_set {
   template <typename> static void check(...);
 
  public:
-  static constexpr const bool value =
+  static constexpr bool value =
       !std::is_void<decltype(check<T>(nullptr))>::value && !is_map<T>::value;
 };
 
 // C array overload
-template <typename T, std::size_t N>
+template <typename T, size_t N>
 auto range_begin(const T (&arr)[N]) -> const T* {
   return arr;
 }
-template <typename T, std::size_t N>
-auto range_end(const T (&arr)[N]) -> const T* {
+template <typename T, size_t N> auto range_end(const T (&arr)[N]) -> const T* {
   return arr + N;
 }
 
@@ -120,7 +118,7 @@ template <typename T> class is_tuple_like_ {
   template <typename> static void check(...);
 
  public:
-  static constexpr const bool value =
+  static constexpr bool value =
       !std::is_void<decltype(check<T>(nullptr))>::value;
 };
 
@@ -154,7 +152,7 @@ using tuple_index_sequence = make_index_sequence<std::tuple_size<T>::value>;
 template <typename T, typename C, bool = is_tuple_like_<T>::value>
 class is_tuple_formattable_ {
  public:
-  static constexpr const bool value = false;
+  static constexpr bool value = false;
 };
 template <typename T, typename C> class is_tuple_formattable_<T, C, true> {
   template <size_t... Is>
@@ -170,7 +168,7 @@ template <typename T, typename C> class is_tuple_formattable_<T, C, true> {
                                        C>::value)...>{}));
 
  public:
-  static constexpr const bool value =
+  static constexpr bool value =
       decltype(check(tuple_index_sequence<T>{}))::value;
 };
 
@@ -208,7 +206,7 @@ template <typename Char, typename... T>
 using result_t = std::tuple<formatter<remove_cvref_t<T>, Char>...>;
 
 using std::get;
-template <typename Tuple, typename Char, std::size_t... Is>
+template <typename Tuple, typename Char, size_t... Is>
 auto get_formatters(index_sequence<Is...>)
     -> result_t<Char, decltype(get<Is>(std::declval<Tuple>()))...>;
 }  // namespace tuple
@@ -219,7 +217,7 @@ template <typename R> struct range_reference_type_impl {
   using type = decltype(*detail::range_begin(std::declval<R&>()));
 };
 
-template <typename T, std::size_t N> struct range_reference_type_impl<T[N]> {
+template <typename T, size_t N> struct range_reference_type_impl<T[N]> {
   using type = T&;
 };
 
@@ -281,14 +279,15 @@ template <typename FormatContext> struct format_tuple_element {
 
 }  // namespace detail
 
+FMT_EXPORT
 template <typename T> struct is_tuple_like {
-  static constexpr const bool value =
+  static constexpr bool value =
       detail::is_tuple_like_<T>::value && !detail::is_range_<T>::value;
 };
 
+FMT_EXPORT
 template <typename T, typename C> struct is_tuple_formattable {
-  static constexpr const bool value =
-      detail::is_tuple_formattable_<T, C>::value;
+  static constexpr bool value = detail::is_tuple_formattable_<T, C>::value;
 };
 
 template <typename Tuple, typename Char>
@@ -343,8 +342,9 @@ struct formatter<Tuple, Char,
   }
 };
 
+FMT_EXPORT
 template <typename T, typename Char> struct is_range {
-  static constexpr const bool value =
+  static constexpr bool value =
       detail::is_range_<T>::value && !detail::has_to_string_view<T>::value;
 };
 
@@ -368,6 +368,7 @@ template <typename P1, typename... Pn>
 struct conjunction<P1, Pn...>
     : conditional_t<bool(P1::value), conjunction<Pn...>, P1> {};
 
+FMT_EXPORT
 template <typename T, typename Char, typename Enable = void>
 struct range_formatter;
 
@@ -670,7 +671,8 @@ struct formatter<join_view<It, Sentinel, Char>, Char> {
   }
 };
 
-template <typename Char, typename Tuple> struct tuple_join_view : detail::view {
+FMT_EXPORT
+template <typename Tuple, typename Char> struct tuple_join_view : detail::view {
   const Tuple& tuple;
   basic_string_view<Char> sep;
 
@@ -685,15 +687,15 @@ template <typename Char, typename Tuple> struct tuple_join_view : detail::view {
 #  define FMT_TUPLE_JOIN_SPECIFIERS 0
 #endif
 
-template <typename Char, typename Tuple>
-struct formatter<tuple_join_view<Char, Tuple>, Char,
+template <typename Tuple, typename Char>
+struct formatter<tuple_join_view<Tuple, Char>, Char,
                  enable_if_t<is_tuple_like<Tuple>::value>> {
   FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) -> const Char* {
     return do_parse(ctx, std::tuple_size<Tuple>());
   }
 
   template <typename FormatContext>
-  auto format(const tuple_join_view<Char, Tuple>& value,
+  auto format(const tuple_join_view<Tuple, Char>& value,
               FormatContext& ctx) const -> typename FormatContext::iterator {
     return do_format(value, ctx, std::tuple_size<Tuple>());
   }
@@ -725,14 +727,14 @@ struct formatter<tuple_join_view<Char, Tuple>, Char,
   }
 
   template <typename FormatContext>
-  auto do_format(const tuple_join_view<Char, Tuple>&, FormatContext& ctx,
+  auto do_format(const tuple_join_view<Tuple, Char>&, FormatContext& ctx,
                  std::integral_constant<size_t, 0>) const ->
       typename FormatContext::iterator {
     return ctx.out();
   }
 
   template <typename FormatContext, size_t N>
-  auto do_format(const tuple_join_view<Char, Tuple>& value, FormatContext& ctx,
+  auto do_format(const tuple_join_view<Tuple, Char>& value, FormatContext& ctx,
                  std::integral_constant<size_t, N>) const ->
       typename FormatContext::iterator {
     using std::get;
@@ -754,7 +756,7 @@ template <typename T> class is_container_adaptor_like {
   template <typename> static void check(...);
 
  public:
-  static constexpr const bool value =
+  static constexpr bool value =
       !std::is_void<decltype(check<T>(nullptr))>::value;
 };
 
@@ -774,13 +776,13 @@ struct formatter<
     : formatter<detail::all<typename T::container_type>, Char> {
   using all = detail::all<typename T::container_type>;
   template <typename FormatContext>
-  auto format(const T& t, FormatContext& ctx) const -> decltype(ctx.out()) {
+  auto format(const T& value, FormatContext& ctx) const -> decltype(ctx.out()) {
     struct getter : T {
-      static auto get(const T& t) -> all {
-        return {t.*(&getter::c)};  // Access c through the derived class.
+      static auto get(const T& v) -> all {
+        return {v.*(&getter::c)};  // Access c through the derived class.
       }
     };
-    return formatter<all>::format(getter::get(t), ctx);
+    return formatter<all>::format(getter::get(value), ctx);
   }
 };
 
@@ -825,7 +827,7 @@ auto join(Range&& r, string_view sep)
  */
 template <typename Tuple, FMT_ENABLE_IF(is_tuple_like<Tuple>::value)>
 FMT_CONSTEXPR auto join(const Tuple& tuple, string_view sep)
-    -> tuple_join_view<char, Tuple> {
+    -> tuple_join_view<Tuple, char> {
   return {tuple, sep};
 }
 
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/std.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/std.h
index 54eb2c2a73..fff6da9dd0 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/std.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/std.h
@@ -15,15 +15,13 @@
 #  include <atomic>
 #  include <bitset>
 #  include <complex>
-#  include <cstdlib>
 #  include <exception>
-#  include <functional>
+#  include <functional>  // std::reference_wrapper
 #  include <memory>
 #  include <thread>
 #  include <type_traits>
-#  include <typeinfo>
-#  include <utility>
-#  include <vector>
+#  include <typeinfo>  // std::type_info
+#  include <utility>   // std::make_index_sequence
 
 // Check FMT_CPLUSPLUS to suppress a bogus warning in MSVC.
 #  if FMT_CPLUSPLUS >= 201703L
@@ -79,11 +77,11 @@
 #  endif
 #endif
 
-#if FMT_CPP_LIB_FILESYSTEM
 FMT_BEGIN_NAMESPACE
-
 namespace detail {
 
+#if FMT_CPP_LIB_FILESYSTEM
+
 template <typename Char, typename PathChar>
 auto get_path_string(const std::filesystem::path& p,
                      const std::basic_string<PathChar>& native) {
@@ -111,9 +109,169 @@ void write_escaped_path(basic_memory_buffer<Char>& quoted,
   }
 }
 
+#endif  // FMT_CPP_LIB_FILESYSTEM
+
+#if defined(__cpp_lib_expected) || FMT_CPP_LIB_VARIANT
+template <typename Char, typename OutputIt, typename T>
+auto write_escaped_alternative(OutputIt out, const T& v) -> OutputIt {
+  if constexpr (has_to_string_view<T>::value)
+    return write_escaped_string<Char>(out, detail::to_string_view(v));
+  if constexpr (std::is_same_v<T, Char>) return write_escaped_char(out, v);
+  return write<Char>(out, v);
+}
+#endif
+
+#if FMT_CPP_LIB_VARIANT
+
+template <typename> struct is_variant_like_ : std::false_type {};
+template <typename... Types>
+struct is_variant_like_<std::variant<Types...>> : std::true_type {};
+
+template <typename Variant, typename Char> class is_variant_formattable {
+  template <size_t... Is>
+  static std::conjunction<
+      is_formattable<std::variant_alternative_t<Is, Variant>, Char>...>
+      check(std::index_sequence<Is...>);
+
+ public:
+  static constexpr bool value = decltype(check(
+      std::make_index_sequence<std::variant_size<Variant>::value>()))::value;
+};
+
+#endif  // FMT_CPP_LIB_VARIANT
+
+#if FMT_USE_RTTI
+
+template <typename Char, typename OutputIt>
+auto write_demangled_name(OutputIt out, const std::type_info& ti) -> OutputIt {
+#  ifdef FMT_HAS_ABI_CXA_DEMANGLE
+  int status = 0;
+  size_t size = 0;
+  std::unique_ptr<char, void (*)(void*)> demangled_name_ptr(
+      abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &std::free);
+
+  string_view demangled_name_view;
+  if (demangled_name_ptr) {
+    demangled_name_view = demangled_name_ptr.get();
+
+    // Normalization of stdlib inline namespace names.
+    // libc++ inline namespaces.
+    //  std::__1::*       -> std::*
+    //  std::__1::__fs::* -> std::*
+    // libstdc++ inline namespaces.
+    //  std::__cxx11::*             -> std::*
+    //  std::filesystem::__cxx11::* -> std::filesystem::*
+    if (demangled_name_view.starts_with("std::")) {
+      char* begin = demangled_name_ptr.get();
+      char* to = begin + 5;  // std::
+      for (char *from = to, *end = begin + demangled_name_view.size();
+           from < end;) {
+        // This is safe, because demangled_name is NUL-terminated.
+        if (from[0] == '_' && from[1] == '_') {
+          char* next = from + 1;
+          while (next < end && *next != ':') next++;
+          if (next[0] == ':' && next[1] == ':') {
+            from = next + 2;
+            continue;
+          }
+        }
+        *to++ = *from++;
+      }
+      demangled_name_view = {begin, detail::to_unsigned(to - begin)};
+    }
+  } else {
+    demangled_name_view = string_view(ti.name());
+  }
+  return detail::write_bytes<Char>(out, demangled_name_view);
+#  elif FMT_MSC_VERSION
+  const string_view demangled_name(ti.name());
+  for (size_t i = 0; i < demangled_name.size(); ++i) {
+    auto sub = demangled_name;
+    sub.remove_prefix(i);
+    if (sub.starts_with("enum ")) {
+      i += 4;
+      continue;
+    }
+    if (sub.starts_with("class ") || sub.starts_with("union ")) {
+      i += 5;
+      continue;
+    }
+    if (sub.starts_with("struct ")) {
+      i += 6;
+      continue;
+    }
+    if (*sub.begin() != ' ') *out++ = *sub.begin();
+  }
+  return out;
+#  else
+  return detail::write_bytes<Char>(out, string_view(ti.name()));
+#  endif
+}
+
+#endif  // FMT_USE_RTTI
+
+template <typename T, typename Enable = void>
+struct has_flip : std::false_type {};
+
+template <typename T>
+struct has_flip<T, void_t<decltype(std::declval<T>().flip())>>
+    : std::true_type {};
+
+template <typename T> struct is_bit_reference_like {
+  static constexpr bool value = std::is_convertible<T, bool>::value &&
+                                std::is_nothrow_assignable<T, bool>::value &&
+                                has_flip<T>::value;
+};
+
+// Workaround for libc++ incompatibility with C++ standard.
+// According to the Standard, `bitset::operator[] const` returns bool.
+#ifdef _LIBCPP_VERSION
+template <typename C>
+struct is_bit_reference_like<std::__bit_const_reference<C>> {
+  static constexpr bool value = true;
+};
+#endif
+
+template <typename T, typename Enable = void>
+struct has_format_as : std::false_type {};
+template <typename T>
+struct has_format_as<T, void_t<decltype(format_as(std::declval<const T&>()))>>
+    : std::true_type {};
+
+template <typename T, typename Enable = void>
+struct has_format_as_member : std::false_type {};
+template <typename T>
+struct has_format_as_member<
+    T, void_t<decltype(formatter<T>::format_as(std::declval<const T&>()))>>
+    : std::true_type {};
+
 }  // namespace detail
 
-FMT_EXPORT
+template <typename T, typename Deleter>
+auto ptr(const std::unique_ptr<T, Deleter>& p) -> const void* {
+  return p.get();
+}
+template <typename T> auto ptr(const std::shared_ptr<T>& p) -> const void* {
+  return p.get();
+}
+
+#if FMT_CPP_LIB_FILESYSTEM
+
+class path : public std::filesystem::path {
+ public:
+  auto display_string() const -> std::string {
+    const std::filesystem::path& base = *this;
+    return fmt::format(FMT_STRING("{}"), base);
+  }
+  auto system_string() const -> std::string { return string(); }
+
+  auto generic_display_string() const -> std::string {
+    const std::filesystem::path& base = *this;
+    return fmt::format(FMT_STRING("{:g}"), base);
+  }
+  auto generic_system_string() const -> std::string { return generic_string(); }
+};
+
 template <typename Char> struct formatter<std::filesystem::path, Char> {
  private:
   format_specs specs_;
@@ -163,40 +321,20 @@ template <typename Char> struct formatter<std::filesystem::path, Char> {
   }
 };
 
-class path : public std::filesystem::path {
- public:
-  auto display_string() const -> std::string {
-    const std::filesystem::path& base = *this;
-    return fmt::format(FMT_STRING("{}"), base);
-  }
-  auto system_string() const -> std::string { return string(); }
-
-  auto generic_display_string() const -> std::string {
-    const std::filesystem::path& base = *this;
-    return fmt::format(FMT_STRING("{:g}"), base);
-  }
-  auto generic_system_string() const -> std::string { return generic_string(); }
-};
-
-FMT_END_NAMESPACE
 #endif  // FMT_CPP_LIB_FILESYSTEM
 
-FMT_BEGIN_NAMESPACE
-FMT_EXPORT
-template <std::size_t N, typename Char>
+template <size_t N, typename Char>
 struct formatter<std::bitset<N>, Char>
     : nested_formatter<basic_string_view<Char>, Char> {
  private:
-  // Functor because C++11 doesn't support generic lambdas.
+  // This is a functor because C++11 doesn't support generic lambdas.
   struct writer {
     const std::bitset<N>& bs;
 
     template <typename OutputIt>
     FMT_CONSTEXPR auto operator()(OutputIt out) -> OutputIt {
-      for (auto pos = N; pos > 0; --pos) {
+      for (auto pos = N; pos > 0; --pos)
         out = detail::write<Char>(out, bs[pos - 1] ? Char('1') : Char('0'));
-      }
-
       return out;
     }
   };
@@ -209,14 +347,10 @@ struct formatter<std::bitset<N>, Char>
   }
 };
 
-FMT_EXPORT
 template <typename Char>
 struct formatter<std::thread::id, Char> : basic_ostream_formatter<Char> {};
-FMT_END_NAMESPACE
 
 #ifdef __cpp_lib_optional
-FMT_BEGIN_NAMESPACE
-FMT_EXPORT
 template <typename T, typename Char>
 struct formatter<std::optional<T>, Char,
                  std::enable_if_t<is_formattable<T, Char>::value>> {
@@ -255,31 +389,9 @@ struct formatter<std::optional<T>, Char,
     return detail::write(out, ')');
   }
 };
-FMT_END_NAMESPACE
 #endif  // __cpp_lib_optional
 
-#if defined(__cpp_lib_expected) || FMT_CPP_LIB_VARIANT
-
-FMT_BEGIN_NAMESPACE
-namespace detail {
-
-template <typename Char, typename OutputIt, typename T>
-auto write_escaped_alternative(OutputIt out, const T& v) -> OutputIt {
-  if constexpr (has_to_string_view<T>::value)
-    return write_escaped_string<Char>(out, detail::to_string_view(v));
-  if constexpr (std::is_same_v<T, Char>) return write_escaped_char(out, v);
-  return write<Char>(out, v);
-}
-
-}  // namespace detail
-
-FMT_END_NAMESPACE
-#endif
-
 #ifdef __cpp_lib_expected
-FMT_BEGIN_NAMESPACE
-
-FMT_EXPORT
 template <typename T, typename E, typename Char>
 struct formatter<std::expected<T, E>, Char,
                  std::enable_if_t<(std::is_void<T>::value ||
@@ -306,12 +418,9 @@ struct formatter<std::expected<T, E>, Char,
     return out;
   }
 };
-FMT_END_NAMESPACE
 #endif  // __cpp_lib_expected
 
 #ifdef __cpp_lib_source_location
-FMT_BEGIN_NAMESPACE
-FMT_EXPORT
 template <> struct formatter<std::source_location> {
   FMT_CONSTEXPR auto parse(parse_context<>& ctx) { return ctx.begin(); }
 
@@ -329,45 +438,14 @@ template <> struct formatter<std::source_location> {
     return out;
   }
 };
-FMT_END_NAMESPACE
 #endif
 
 #if FMT_CPP_LIB_VARIANT
-FMT_BEGIN_NAMESPACE
-namespace detail {
-
-template <typename T>
-using variant_index_sequence =
-    std::make_index_sequence<std::variant_size<T>::value>;
-
-template <typename> struct is_variant_like_ : std::false_type {};
-template <typename... Types>
-struct is_variant_like_<std::variant<Types...>> : std::true_type {};
-
-// formattable element check.
-template <typename T, typename C> class is_variant_formattable_ {
-  template <std::size_t... Is>
-  static std::conjunction<
-      is_formattable<std::variant_alternative_t<Is, T>, C>...>
-      check(std::index_sequence<Is...>);
-
- public:
-  static constexpr const bool value =
-      decltype(check(variant_index_sequence<T>{}))::value;
-};
-
-}  // namespace detail
 
 template <typename T> struct is_variant_like {
-  static constexpr const bool value = detail::is_variant_like_<T>::value;
+  static constexpr bool value = detail::is_variant_like_<T>::value;
 };
 
-template <typename T, typename C> struct is_variant_formattable {
-  static constexpr const bool value =
-      detail::is_variant_formattable_<T, C>::value;
-};
-
-FMT_EXPORT
 template <typename Char> struct formatter<std::monostate, Char> {
   FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) -> const Char* {
     return ctx.begin();
@@ -380,12 +458,11 @@ template <typename Char> struct formatter<std::monostate, Char> {
   }
 };
 
-FMT_EXPORT
 template <typename Variant, typename Char>
-struct formatter<
-    Variant, Char,
-    std::enable_if_t<std::conjunction_v<
-        is_variant_like<Variant>, is_variant_formattable<Variant, Char>>>> {
+struct formatter<Variant, Char,
+                 std::enable_if_t<std::conjunction_v<
+                     is_variant_like<Variant>,
+                     detail::is_variant_formattable<Variant, Char>>>> {
   FMT_CONSTEXPR auto parse(parse_context<Char>& ctx) -> const Char* {
     return ctx.begin();
   }
@@ -410,15 +487,14 @@ struct formatter<
     return out;
   }
 };
-FMT_END_NAMESPACE
+
 #endif  // FMT_CPP_LIB_VARIANT
 
-FMT_BEGIN_NAMESPACE
-FMT_EXPORT
 template <> struct formatter<std::error_code> {
  private:
   format_specs specs_;
   detail::arg_ref<char> width_ref_;
+  bool debug_ = false;
 
  public:
   FMT_CONSTEXPR auto parse(parse_context<>& ctx) -> const char* {
@@ -426,11 +502,19 @@ template <> struct formatter<std::error_code> {
     if (it == end) return it;
 
     it = detail::parse_align(it, end, specs_);
-    if (it == end) return it;
 
     char c = *it;
-    if ((c >= '0' && c <= '9') || c == '{')
+    if (it != end && ((c >= '0' && c <= '9') || c == '{'))
       it = detail::parse_width(it, end, specs_, width_ref_, ctx);
+
+    if (it != end && *it == '?') {
+      debug_ = true;
+      ++it;
+    }
+    if (it != end && *it == 's') {
+      specs_.set_type(presentation_type::string);
+      ++it;
+    }
     return it;
   }
 
@@ -440,87 +524,25 @@ template <> struct formatter<std::error_code> {
     auto specs = specs_;
     detail::handle_dynamic_spec(specs.dynamic_width(), specs.width, width_ref_,
                                 ctx);
-    memory_buffer buf;
-    buf.append(string_view(ec.category().name()));
-    buf.push_back(':');
-    detail::write<char>(appender(buf), ec.value());
-    return detail::write<char>(ctx.out(), string_view(buf.data(), buf.size()),
-                               specs);
+    auto buf = memory_buffer();
+    if (specs_.type() == presentation_type::string) {
+      buf.append(ec.message());
+    } else {
+      buf.append(string_view(ec.category().name()));
+      buf.push_back(':');
+      detail::write<char>(appender(buf), ec.value());
+    }
+    auto quoted = memory_buffer();
+    auto str = string_view(buf.data(), buf.size());
+    if (debug_) {
+      detail::write_escaped_string<char>(std::back_inserter(quoted), str);
+      str = string_view(quoted.data(), quoted.size());
+    }
+    return detail::write<char>(ctx.out(), str, specs);
   }
 };
 
 #if FMT_USE_RTTI
-namespace detail {
-
-template <typename Char, typename OutputIt>
-auto write_demangled_name(OutputIt out, const std::type_info& ti) -> OutputIt {
-#  ifdef FMT_HAS_ABI_CXA_DEMANGLE
-  int status = 0;
-  std::size_t size = 0;
-  std::unique_ptr<char, void (*)(void*)> demangled_name_ptr(
-      abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &std::free);
-
-  string_view demangled_name_view;
-  if (demangled_name_ptr) {
-    demangled_name_view = demangled_name_ptr.get();
-
-    // Normalization of stdlib inline namespace names.
-    // libc++ inline namespaces.
-    //  std::__1::*       -> std::*
-    //  std::__1::__fs::* -> std::*
-    // libstdc++ inline namespaces.
-    //  std::__cxx11::*             -> std::*
-    //  std::filesystem::__cxx11::* -> std::filesystem::*
-    if (demangled_name_view.starts_with("std::")) {
-      char* begin = demangled_name_ptr.get();
-      char* to = begin + 5;  // std::
-      for (char *from = to, *end = begin + demangled_name_view.size();
-           from < end;) {
-        // This is safe, because demangled_name is NUL-terminated.
-        if (from[0] == '_' && from[1] == '_') {
-          char* next = from + 1;
-          while (next < end && *next != ':') next++;
-          if (next[0] == ':' && next[1] == ':') {
-            from = next + 2;
-            continue;
-          }
-        }
-        *to++ = *from++;
-      }
-      demangled_name_view = {begin, detail::to_unsigned(to - begin)};
-    }
-  } else {
-    demangled_name_view = string_view(ti.name());
-  }
-  return detail::write_bytes<Char>(out, demangled_name_view);
-#  elif FMT_MSC_VERSION
-  const string_view demangled_name(ti.name());
-  for (std::size_t i = 0; i < demangled_name.size(); ++i) {
-    auto sub = demangled_name;
-    sub.remove_prefix(i);
-    if (sub.starts_with("enum ")) {
-      i += 4;
-      continue;
-    }
-    if (sub.starts_with("class ") || sub.starts_with("union ")) {
-      i += 5;
-      continue;
-    }
-    if (sub.starts_with("struct ")) {
-      i += 6;
-      continue;
-    }
-    if (*sub.begin() != ' ') *out++ = *sub.begin();
-  }
-  return out;
-#  else
-  return detail::write_bytes<Char>(out, string_view(ti.name()));
-#  endif
-}
-
-}  // namespace detail
-
-FMT_EXPORT
 template <typename Char>
 struct formatter<std::type_info, Char  // DEPRECATED! Mixing code unit types.
                  > {
@@ -535,9 +557,8 @@ struct formatter<std::type_info, Char  // DEPRECATED! Mixing code unit types.
     return detail::write_demangled_name<Char>(ctx.out(), ti);
   }
 };
-#endif
+#endif  // FMT_USE_RTTI
 
-FMT_EXPORT
 template <typename T, typename Char>
 struct formatter<
     T, Char,  // DEPRECATED! Mixing code unit types.
@@ -572,38 +593,9 @@ struct formatter<
   }
 };
 
-namespace detail {
-
-template <typename T, typename Enable = void>
-struct has_flip : std::false_type {};
-
-template <typename T>
-struct has_flip<T, void_t<decltype(std::declval<T>().flip())>>
-    : std::true_type {};
-
-template <typename T> struct is_bit_reference_like {
-  static constexpr const bool value =
-      std::is_convertible<T, bool>::value &&
-      std::is_nothrow_assignable<T, bool>::value && has_flip<T>::value;
-};
-
-#ifdef _LIBCPP_VERSION
-
-// Workaround for libc++ incompatibility with C++ standard.
-// According to the Standard, `bitset::operator[] const` returns bool.
-template <typename C>
-struct is_bit_reference_like<std::__bit_const_reference<C>> {
-  static constexpr const bool value = true;
-};
-
-#endif
-
-}  // namespace detail
-
 // We can't use std::vector<bool, Allocator>::reference and
 // std::bitset<N>::reference because the compiler can't deduce Allocator and N
 // in partial specialization.
-FMT_EXPORT
 template <typename BitRef, typename Char>
 struct formatter<BitRef, Char,
                  enable_if_t<detail::is_bit_reference_like<BitRef>::value>>
@@ -615,15 +607,6 @@ struct formatter<BitRef, Char,
   }
 };
 
-template <typename T, typename Deleter>
-auto ptr(const std::unique_ptr<T, Deleter>& p) -> const void* {
-  return p.get();
-}
-template <typename T> auto ptr(const std::shared_ptr<T>& p) -> const void* {
-  return p.get();
-}
-
-FMT_EXPORT
 template <typename T, typename Char>
 struct formatter<std::atomic<T>, Char,
                  enable_if_t<is_formattable<T, Char>::value>>
@@ -636,7 +619,6 @@ struct formatter<std::atomic<T>, Char,
 };
 
 #ifdef __cpp_lib_atomic_flag_test
-FMT_EXPORT
 template <typename Char>
 struct formatter<std::atomic_flag, Char> : formatter<bool, Char> {
   template <typename FormatContext>
@@ -647,7 +629,6 @@ struct formatter<std::atomic_flag, Char> : formatter<bool, Char> {
 };
 #endif  // __cpp_lib_atomic_flag_test
 
-FMT_EXPORT
 template <typename T, typename Char> struct formatter<std::complex<T>, Char> {
  private:
   detail::dynamic_format_specs<Char> specs_;
@@ -710,10 +691,13 @@ template <typename T, typename Char> struct formatter<std::complex<T>, Char> {
   }
 };
 
-FMT_EXPORT
 template <typename T, typename Char>
 struct formatter<std::reference_wrapper<T>, Char,
-                 enable_if_t<is_formattable<remove_cvref_t<T>, Char>::value>>
+                 // Guard against format_as because reference_wrapper is
+                 // implicitly convertible to T&.
+                 enable_if_t<is_formattable<remove_cvref_t<T>, Char>::value &&
+                             !detail::has_format_as<T>::value &&
+                             !detail::has_format_as_member<T>::value>>
     : formatter<remove_cvref_t<T>, Char> {
   template <typename FormatContext>
   auto format(std::reference_wrapper<T> ref, FormatContext& ctx) const
@@ -723,4 +707,5 @@ struct formatter<std::reference_wrapper<T>, Char,
 };
 
 FMT_END_NAMESPACE
+
 #endif  // FMT_STD_H_
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/xchar.h b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/xchar.h
index 9f7f889d64..598fea7571 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/xchar.h
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/include/fmt/xchar.h
@@ -112,10 +112,6 @@ inline auto runtime(wstring_view s) -> runtime_format_string<wchar_t> {
   return {{s}};
 }
 
-template <> struct is_char<wchar_t> : std::true_type {};
-template <> struct is_char<char16_t> : std::true_type {};
-template <> struct is_char<char32_t> : std::true_type {};
-
 #ifdef __cpp_char8_t
 template <> struct is_char<char8_t> : bool_constant<detail::is_utf8_enabled> {};
 #endif
@@ -155,7 +151,7 @@ auto join(std::initializer_list<T> list, wstring_view sep)
 
 template <typename Tuple, FMT_ENABLE_IF(is_tuple_like<Tuple>::value)>
 auto join(const Tuple& tuple, basic_string_view<wchar_t> sep)
-    -> tuple_join_view<wchar_t, Tuple> {
+    -> tuple_join_view<Tuple, wchar_t> {
   return {tuple, sep};
 }
 
@@ -322,7 +318,7 @@ template <typename... T> void println(wformat_string<T...> fmt, T&&... args) {
   return print(L"{}\n", fmt::format(fmt, std::forward<T>(args)...));
 }
 
-inline auto vformat(const text_style& ts, wstring_view fmt, wformat_args args)
+inline auto vformat(text_style ts, wstring_view fmt, wformat_args args)
     -> std::wstring {
   auto buf = wmemory_buffer();
   detail::vformat_to(buf, ts, fmt, args);
@@ -330,19 +326,19 @@ inline auto vformat(const text_style& ts, wstring_view fmt, wformat_args args)
 }
 
 template <typename... T>
-inline auto format(const text_style& ts, wformat_string<T...> fmt, T&&... args)
+inline auto format(text_style ts, wformat_string<T...> fmt, T&&... args)
     -> std::wstring {
   return fmt::vformat(ts, fmt, fmt::make_wformat_args(args...));
 }
 
 template <typename... T>
-FMT_DEPRECATED void print(std::FILE* f, const text_style& ts,
-                          wformat_string<T...> fmt, const T&... args) {
+FMT_DEPRECATED void print(std::FILE* f, text_style ts, wformat_string<T...> fmt,
+                          const T&... args) {
   vprint(f, ts, fmt, fmt::make_wformat_args(args...));
 }
 
 template <typename... T>
-FMT_DEPRECATED void print(const text_style& ts, wformat_string<T...> fmt,
+FMT_DEPRECATED void print(text_style ts, wformat_string<T...> fmt,
                           const T&... args) {
   return print(stdout, ts, fmt, args...);
 }
diff --git a/wpiutil/src/main/native/thirdparty/fmtlib/src/os.cpp b/wpiutil/src/main/native/thirdparty/fmtlib/src/os.cpp
index c833a05141..740e345d3d 100644
--- a/wpiutil/src/main/native/thirdparty/fmtlib/src/os.cpp
+++ b/wpiutil/src/main/native/thirdparty/fmtlib/src/os.cpp
@@ -66,14 +66,14 @@ using rwresult = int;
 
 // On Windows the count argument to read and write is unsigned, so convert
 // it from size_t preventing integer overflow.
-inline unsigned convert_rwcount(std::size_t count) {
+inline unsigned convert_rwcount(size_t count) {
   return count <= UINT_MAX ? static_cast<unsigned>(count) : UINT_MAX;
 }
 #elif FMT_USE_FCNTL
 // Return type of read and write functions.
 using rwresult = ssize_t;
 
-inline std::size_t convert_rwcount(std::size_t count) { return count; }
+inline size_t convert_rwcount(size_t count) { return count; }
 #endif
 }  // namespace
 
@@ -266,7 +266,7 @@ long long file::size() const {
 #  endif
 }
 
-std::size_t file::read(void* buffer, std::size_t count) {
+size_t file::read(void* buffer, size_t count) {
   rwresult result = 0;
   FMT_RETRY(result, FMT_POSIX_CALL(read(fd_, buffer, convert_rwcount(count))));
   if (result < 0)
@@ -274,7 +274,7 @@ std::size_t file::read(void* buffer, std::size_t count) {
   return detail::to_unsigned(result);
 }
 
-std::size_t file::write(const void* buffer, std::size_t count) {
+size_t file::write(const void* buffer, size_t count) {
   rwresult result = 0;
   FMT_RETRY(result, FMT_POSIX_CALL(write(fd_, buffer, convert_rwcount(count))));
   if (result < 0)