diff --git a/libcxx/include/__chrono/formatter.h b/libcxx/include/__chrono/formatter.h
--- a/libcxx/include/__chrono/formatter.h
+++ b/libcxx/include/__chrono/formatter.h
@@ -485,12 +485,12 @@
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
 
-template <class _CharT, class _Tp>
+template <class _CharT, class _Tp, class _FormatContext>
 _LIBCPP_HIDE_FROM_ABI auto
 __format_chrono(const _Tp& __value,
-                auto& __ctx,
+                _FormatContext& __ctx,
                 __format_spec::__parsed_specifications<_CharT> __specs,
-                basic_string_view<_CharT> __chrono_specs) -> decltype(__ctx.out()) {
+                basic_string_view<_CharT> __chrono_specs) {
   basic_stringstream<_CharT> __sstr;
   // [time.format]/2
   // 2.1 - the "C" locale if the L option is not present in chrono-format-spec, otherwise
@@ -566,14 +566,14 @@
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS __formatter_chrono {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto __parse(
-      basic_format_parse_context<_CharT>& __parse_ctx, __format_spec::__fields __fields, __format_spec::__flags __flags)
-      -> decltype(__parse_ctx.begin()) {
-    return __parser_.__parse(__parse_ctx, __fields, __flags);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator
+  __parse(_ParseContext& __ctx, __format_spec::__fields __fields, __format_spec::__flags __flags) {
+    return __parser_.__parse(__ctx, __fields, __flags);
   }
 
-  template <class _Tp>
-  _LIBCPP_HIDE_FROM_ABI auto format(const _Tp& __value, auto& __ctx) const -> decltype(__ctx.out()) const {
+  template <class _Tp, class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(const _Tp& __value, _FormatContext& __ctx) const {
     return __formatter::__format_chrono(
         __value, __ctx, __parser_.__parser_.__get_parsed_chrono_specifications(__ctx), __parser_.__chrono_specs_);
   }
@@ -586,9 +586,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__clock);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__clock);
   }
 };
 
@@ -597,9 +597,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__clock);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__clock);
   }
 };
 
@@ -608,10 +608,10 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     // The flags are not __clock since there is no associated time-zone.
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date_time);
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date_time);
   }
 };
 
@@ -620,8 +620,8 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
     // [time.format]/1
     // Giving a precision specification in the chrono-format-spec is valid only
     // for std::chrono::duration types where the representation type Rep is a
@@ -631,9 +631,9 @@
     //
     // Note this doesn't refer to chrono::treat_as_floating_point_v<_Rep>.
     if constexpr (std::floating_point<_Rep>)
-      return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono_fractional, __format_spec::__flags::__duration);
+      return _Base::__parse(__ctx, __format_spec::__fields_chrono_fractional, __format_spec::__flags::__duration);
     else
-      return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__duration);
+      return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__duration);
   }
 };
 
@@ -643,9 +643,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__day);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__day);
   }
 };
 
@@ -655,9 +655,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month);
   }
 };
 
@@ -667,9 +667,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__year);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__year);
   }
 };
 
@@ -679,9 +679,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
   }
 };
 
@@ -691,9 +691,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
   }
 };
 
@@ -703,9 +703,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__weekday);
   }
 };
 
@@ -715,9 +715,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_day);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_day);
   }
 };
 
@@ -727,9 +727,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month);
   }
 };
 
@@ -739,9 +739,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_weekday);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_weekday);
   }
 };
 
@@ -751,9 +751,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_weekday);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__month_weekday);
   }
 };
 
@@ -763,9 +763,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__year_month);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__year_month);
   }
 };
 
@@ -775,9 +775,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
   }
 };
 
@@ -787,9 +787,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
   }
 };
 
@@ -799,9 +799,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
   }
 };
 
@@ -811,9 +811,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__date);
   }
 };
 
@@ -822,9 +822,9 @@
 public:
   using _Base = __formatter_chrono<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__time);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__time);
   }
 };
 #endif // if _LIBCPP_STD_VER >= 20 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
diff --git a/libcxx/include/__chrono/parser_std_format_spec.h b/libcxx/include/__chrono/parser_std_format_spec.h
--- a/libcxx/include/__chrono/parser_std_format_spec.h
+++ b/libcxx/include/__chrono/parser_std_format_spec.h
@@ -140,11 +140,11 @@
   using _ConstIterator = typename basic_format_parse_context<_CharT>::const_iterator;
 
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto
-  __parse(basic_format_parse_context<_CharT>& __parse_ctx, __fields __fields, __flags __flags)
-      -> decltype(__parse_ctx.begin()) {
-    _ConstIterator __begin = __parser_.__parse(__parse_ctx, __fields);
-    _ConstIterator __end   = __parse_ctx.end();
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator
+  __parse(_ParseContext& __ctx, __fields __fields, __flags __flags) {
+    _ConstIterator __begin = __parser_.__parse(__ctx, __fields);
+    _ConstIterator __end   = __ctx.end();
     if (__begin == __end)
       return __begin;
 
diff --git a/libcxx/include/__format/format_functions.h b/libcxx/include/__format/format_functions.h
--- a/libcxx/include/__format/format_functions.h
+++ b/libcxx/include/__format/format_functions.h
@@ -89,14 +89,16 @@
 template <class _CharT>
 class _LIBCPP_TEMPLATE_VIS __compile_time_handle {
 public:
-  _LIBCPP_HIDE_FROM_ABI
-  constexpr void __parse(basic_format_parse_context<_CharT>& __parse_ctx) const { __parse_(__parse_ctx); }
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr void __parse(_ParseContext& __ctx) const {
+    __parse_(__ctx);
+  }
 
   template <class _Tp>
   _LIBCPP_HIDE_FROM_ABI constexpr void __enable() {
-    __parse_ = [](basic_format_parse_context<_CharT>& __parse_ctx) {
+    __parse_ = [](basic_format_parse_context<_CharT>& __ctx) {
       formatter<_Tp, _CharT> __f;
-      __parse_ctx.advance_to(__f.parse(__parse_ctx));
+      __ctx.advance_to(__f.parse(__ctx));
     };
   }
 
diff --git a/libcxx/include/__format/formatter_bool.h b/libcxx/include/__format/formatter_bool.h
--- a/libcxx/include/__format/formatter_bool.h
+++ b/libcxx/include/__format/formatter_bool.h
@@ -38,14 +38,15 @@
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<bool, _CharT> {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto
-  parse(basic_format_parse_context<_CharT>& __parse_ctx) -> decltype(__parse_ctx.begin()) {
-    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_integral);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_integral);
     __format_spec::__process_parsed_bool(__parser_);
     return __result;
   }
 
-  _LIBCPP_HIDE_FROM_ABI auto format(bool __value, auto& __ctx) const -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(bool __value, _FormatContext& __ctx) const {
     switch (__parser_.__type_) {
     case __format_spec::__type::__default:
     case __format_spec::__type::__string:
diff --git a/libcxx/include/__format/formatter_char.h b/libcxx/include/__format/formatter_char.h
--- a/libcxx/include/__format/formatter_char.h
+++ b/libcxx/include/__format/formatter_char.h
@@ -33,14 +33,15 @@
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS __formatter_char {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto
-  parse(basic_format_parse_context<_CharT>& __parse_ctx) -> decltype(__parse_ctx.begin()) {
-    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_integral);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_integral);
     __format_spec::__process_parsed_char(__parser_);
     return __result;
   }
 
-  _LIBCPP_HIDE_FROM_ABI auto format(_CharT __value, auto& __ctx) const -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_CharT __value, _FormatContext& __ctx) const {
     if (__parser_.__type_ == __format_spec::__type::__default || __parser_.__type_ == __format_spec::__type::__char)
       return __formatter::__format_char(__value, __ctx.out(), __parser_.__get_parsed_std_specifications(__ctx));
 
@@ -60,7 +61,8 @@
       return __formatter::__format_integer(__value, __ctx, __parser_.__get_parsed_std_specifications(__ctx));
   }
 
-  _LIBCPP_HIDE_FROM_ABI auto format(char __value, auto& __ctx) const -> decltype(__ctx.out())
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(char __value, _FormatContext& __ctx) const
     requires(same_as<_CharT, wchar_t>)
   {
     return format(static_cast<wchar_t>(__value), __ctx);
diff --git a/libcxx/include/__format/formatter_floating_point.h b/libcxx/include/__format/formatter_floating_point.h
--- a/libcxx/include/__format/formatter_floating_point.h
+++ b/libcxx/include/__format/formatter_floating_point.h
@@ -608,10 +608,9 @@
   return __formatter::__write(__buffer, __last, _VSTD::move(__out_it), __specs);
 }
 
-template <floating_point _Tp, class _CharT>
-_LIBCPP_HIDE_FROM_ABI auto
-__format_floating_point(_Tp __value, auto& __ctx, __format_spec::__parsed_specifications<_CharT> __specs)
-    -> decltype(__ctx.out()) {
+template <floating_point _Tp, class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+__format_floating_point(_Tp __value, _FormatContext& __ctx, __format_spec::__parsed_specifications<_CharT> __specs) {
   bool __negative = _VSTD::signbit(__value);
 
   if (!_VSTD::isfinite(__value)) [[unlikely]]
@@ -728,15 +727,15 @@
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS __formatter_floating_point {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto
-  parse(basic_format_parse_context<_CharT>& __parse_ctx) -> decltype(__parse_ctx.begin()) {
-    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_floating_point);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_floating_point);
     __format_spec::__process_parsed_floating_point(__parser_);
     return __result;
   }
 
-  template <floating_point _Tp>
-  _LIBCPP_HIDE_FROM_ABI auto format(_Tp __value, auto& __ctx) const -> decltype(__ctx.out()) {
+  template <floating_point _Tp, class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_Tp __value, _FormatContext& __ctx) const {
     return __formatter::__format_floating_point(__value, __ctx, __parser_.__get_parsed_std_specifications(__ctx));
   }
 
diff --git a/libcxx/include/__format/formatter_integer.h b/libcxx/include/__format/formatter_integer.h
--- a/libcxx/include/__format/formatter_integer.h
+++ b/libcxx/include/__format/formatter_integer.h
@@ -34,15 +34,15 @@
     struct _LIBCPP_TEMPLATE_VIS __formatter_integer {
 
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto
-  parse(basic_format_parse_context<_CharT>& __parse_ctx) -> decltype(__parse_ctx.begin()) {
-    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_integral);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_integral);
     __format_spec::__process_parsed_integer(__parser_);
     return __result;
   }
 
-  template <integral _Tp>
-  _LIBCPP_HIDE_FROM_ABI auto format(_Tp __value, auto& __ctx) const -> decltype(__ctx.out()) {
+  template <integral _Tp, class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_Tp __value, _FormatContext& __ctx) const {
     __format_spec::__parsed_specifications<_CharT> __specs = __parser_.__get_parsed_std_specifications(__ctx);
 
     if (__specs.__std_.__type_ == __format_spec::__type::__char)
diff --git a/libcxx/include/__format/formatter_integral.h b/libcxx/include/__format/formatter_integral.h
--- a/libcxx/include/__format/formatter_integral.h
+++ b/libcxx/include/__format/formatter_integral.h
@@ -203,16 +203,16 @@
        + 1;                          // Reserve space for the sign.
 }
 
-template <unsigned_integral _Tp, class _CharT>
-_LIBCPP_HIDE_FROM_ABI auto __format_integer(
+template <unsigned_integral _Tp, class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator __format_integer(
     _Tp __value,
-    auto& __ctx,
+    _FormatContext& __ctx,
     __format_spec::__parsed_specifications<_CharT> __specs,
     bool __negative,
     char* __begin,
     char* __end,
     const char* __prefix,
-    int __base) -> decltype(__ctx.out()) {
+    int __base) {
   char* __first = __formatter::__insert_sign(__begin, __negative, __specs.__std_.__sign_);
   if (__specs.__std_.__alternate_form_ && __prefix)
     while (*__prefix)
@@ -263,10 +263,12 @@
   return __formatter::__write_transformed(__first, __last, __ctx.out(), __specs, __formatter::__hex_to_upper);
 }
 
-template <unsigned_integral _Tp, class _CharT>
-_LIBCPP_HIDE_FROM_ABI auto __format_integer(
-    _Tp __value, auto& __ctx, __format_spec::__parsed_specifications<_CharT> __specs, bool __negative = false)
-    -> decltype(__ctx.out()) {
+template <unsigned_integral _Tp, class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+__format_integer(_Tp __value,
+                 _FormatContext& __ctx,
+                 __format_spec::__parsed_specifications<_CharT> __specs,
+                 bool __negative = false) {
   switch (__specs.__std_.__type_) {
   case __format_spec::__type::__binary_lower_case: {
     array<char, __formatter::__buffer_size<decltype(__value), 2>()> __array;
@@ -302,10 +304,9 @@
   }
 }
 
-template <signed_integral _Tp, class _CharT>
-_LIBCPP_HIDE_FROM_ABI auto
-__format_integer(_Tp __value, auto& __ctx, __format_spec::__parsed_specifications<_CharT> __specs)
-    -> decltype(__ctx.out()) {
+template <signed_integral _Tp, class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+__format_integer(_Tp __value, _FormatContext& __ctx, __format_spec::__parsed_specifications<_CharT> __specs) {
   // Depending on the std-format-spec string the sign and the value
   // might not be outputted together:
   // - alternate form may insert a prefix string.
@@ -341,10 +342,9 @@
 };
 #  endif
 
-template <class _CharT>
-_LIBCPP_HIDE_FROM_ABI auto
-__format_bool(bool __value, auto& __ctx, __format_spec::__parsed_specifications<_CharT> __specs)
-    -> decltype(__ctx.out()) {
+template <class _CharT, class _FormatContext>
+_LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+__format_bool(bool __value, _FormatContext& __ctx, __format_spec::__parsed_specifications<_CharT> __specs) {
 #  ifndef _LIBCPP_HAS_NO_LOCALIZATION
   if (__specs.__std_.__locale_specific_form_) {
     const auto& __np           = std::use_facet<numpunct<_CharT>>(__ctx.locale());
diff --git a/libcxx/include/__format/formatter_pointer.h b/libcxx/include/__format/formatter_pointer.h
--- a/libcxx/include/__format/formatter_pointer.h
+++ b/libcxx/include/__format/formatter_pointer.h
@@ -32,14 +32,15 @@
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS __formatter_pointer {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto
-  parse(basic_format_parse_context<_CharT>& __parse_ctx) -> decltype(__parse_ctx.begin()) {
-    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_pointer);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_pointer);
     __format_spec::__process_display_type_pointer(__parser_.__type_);
     return __result;
   }
 
-  _LIBCPP_HIDE_FROM_ABI auto format(const void* __ptr, auto& __ctx) const -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(const void* __ptr, _FormatContext& __ctx) const {
     __format_spec::__parsed_specifications<_CharT> __specs = __parser_.__get_parsed_std_specifications(__ctx);
     __specs.__std_.__alternate_form_                       = true;
     __specs.__std_.__type_                                 = __format_spec::__type::__hexadecimal_lower_case;
diff --git a/libcxx/include/__format/formatter_string.h b/libcxx/include/__format/formatter_string.h
--- a/libcxx/include/__format/formatter_string.h
+++ b/libcxx/include/__format/formatter_string.h
@@ -32,14 +32,16 @@
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS __formatter_string {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-      -> decltype(__parse_ctx.begin()) {
-    auto __result = __parser_.__parse(__parse_ctx, __format_spec::__fields_string);
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    typename _ParseContext::iterator __result = __parser_.__parse(__ctx, __format_spec::__fields_string);
     __format_spec::__process_display_type_string(__parser_.__type_);
     return __result;
   }
 
-  _LIBCPP_HIDE_FROM_ABI auto format(basic_string_view<_CharT> __str, auto& __ctx) const -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(basic_string_view<_CharT> __str, _FormatContext& __ctx) const {
 #  if _LIBCPP_STD_VER >= 23
     if (__parser_.__type_ == __format_spec::__type::__debug)
       return __formatter::__format_escaped_string(__str, __ctx.out(), __parser_.__get_parsed_std_specifications(__ctx));
@@ -61,7 +63,8 @@
     : public __formatter_string<_CharT> {
   using _Base = __formatter_string<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI auto format(const _CharT* __str, auto& __ctx) const -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(const _CharT* __str, _FormatContext& __ctx) const {
     _LIBCPP_ASSERT(__str, "The basic_format_arg constructor should have "
                           "prevented an invalid pointer.");
 
@@ -99,7 +102,8 @@
     : public formatter<const _CharT*, _CharT> {
   using _Base = formatter<const _CharT*, _CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI auto format(_CharT* __str, auto& __ctx) const -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_CharT* __str, _FormatContext& __ctx) const {
     return _Base::format(__str, __ctx);
   }
 };
@@ -110,7 +114,8 @@
     : public __formatter_string<_CharT> {
   using _Base = __formatter_string<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI auto format(_CharT __str[_Size], auto& __ctx) const -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(_CharT __str[_Size], _FormatContext& __ctx) const {
     return _Base::format(basic_string_view<_CharT>(__str, _Size), __ctx);
   }
 };
@@ -121,8 +126,9 @@
     : public __formatter_string<_CharT> {
   using _Base = __formatter_string<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI auto format(const basic_string<_CharT, _Traits, _Allocator>& __str, auto& __ctx) const
-      -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(const basic_string<_CharT, _Traits, _Allocator>& __str, _FormatContext& __ctx) const {
     // Drop _Traits and _Allocator to have one std::basic_string formatter.
     return _Base::format(basic_string_view<_CharT>(__str.data(), __str.size()), __ctx);
   }
@@ -134,8 +140,9 @@
     : public __formatter_string<_CharT> {
   using _Base = __formatter_string<_CharT>;
 
-  _LIBCPP_HIDE_FROM_ABI auto format(basic_string_view<_CharT, _Traits> __str, auto& __ctx) const
-      -> decltype(__ctx.out()) {
+  template <class _FormatContext>
+  _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator
+  format(basic_string_view<_CharT, _Traits> __str, _FormatContext& __ctx) const {
     // Drop _Traits to have one std::basic_string_view formatter.
     return _Base::format(basic_string_view<_CharT>(__str.data(), __str.size()), __ctx);
   }
diff --git a/libcxx/include/__format/formatter_tuple.h b/libcxx/include/__format/formatter_tuple.h
--- a/libcxx/include/__format/formatter_tuple.h
+++ b/libcxx/include/__format/formatter_tuple.h
@@ -50,10 +50,10 @@
   }
 
   template <class _ParseContext>
-  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __parse_ctx) {
-    auto __begin = __parser_.__parse(__parse_ctx, __format_spec::__fields_tuple);
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    auto __begin = __parser_.__parse(__ctx, __format_spec::__fields_tuple);
 
-    auto __end = __parse_ctx.end();
+    auto __end = __ctx.end();
     if (__begin != __end) {
       if (*__begin == _CharT('m')) {
         if constexpr (sizeof...(_Args) == 2) {
@@ -71,14 +71,14 @@
     if (__begin != __end && *__begin != _CharT('}'))
       std::__throw_format_error("The format-spec should consume the input or end with a '}'");
 
-    __parse_ctx.advance_to(__begin);
+    __ctx.advance_to(__begin);
 
     // [format.tuple]/7
     //   ... For each element e in underlying_, if e.set_debug_format()
     //   is a valid expression, calls e.set_debug_format().
     std::__for_each_index_sequence(make_index_sequence<sizeof...(_Args)>(), [&]<size_t _Index> {
       auto& __formatter = std::get<_Index>(__underlying_);
-      __formatter.parse(__parse_ctx);
+      __formatter.parse(__ctx);
       // Unlike the range_formatter we don't guard against evil parsers. Since
       // this format-spec never has a format-spec for the underlying type
       // adding the test would give additional overhead.
diff --git a/libcxx/include/__format/parser_std_format_spec.h b/libcxx/include/__format/parser_std_format_spec.h
--- a/libcxx/include/__format/parser_std_format_spec.h
+++ b/libcxx/include/__format/parser_std_format_spec.h
@@ -50,16 +50,16 @@
 
 namespace __format_spec {
 
-template <contiguous_iterator _Iterator>
+template <contiguous_iterator _Iterator, class _ParseContext>
 _LIBCPP_HIDE_FROM_ABI constexpr __format::__parse_number_result<_Iterator>
-__parse_arg_id(_Iterator __begin, _Iterator __end, auto& __parse_ctx) {
+__parse_arg_id(_Iterator __begin, _Iterator __end, _ParseContext& __ctx) {
   using _CharT = iter_value_t<_Iterator>;
   // This function is a wrapper to call the real parser. But it does the
   // validation for the pre-conditions and post-conditions.
   if (__begin == __end)
     std::__throw_format_error("End of input while parsing format-spec arg-id");
 
-  __format::__parse_number_result __r = __format::__parse_arg_id(__begin, __end, __parse_ctx);
+  __format::__parse_number_result __r = __format::__parse_arg_id(__begin, __end, __ctx);
 
   if (__r.__last == __end || *__r.__last != _CharT('}'))
     std::__throw_format_error("Invalid arg-id");
@@ -282,11 +282,10 @@
 template <class _CharT>
 class _LIBCPP_TEMPLATE_VIS __parser {
 public:
-  _LIBCPP_HIDE_FROM_ABI constexpr auto __parse(basic_format_parse_context<_CharT>& __parse_ctx, __fields __fields)
-      -> decltype(__parse_ctx.begin()) {
-
-    auto __begin = __parse_ctx.begin();
-    auto __end = __parse_ctx.end();
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator __parse(_ParseContext& __ctx, __fields __fields) {
+    auto __begin = __ctx.begin();
+    auto __end   = __ctx.end();
     if (__begin == __end)
       return __begin;
 
@@ -302,10 +301,10 @@
     if (__fields.__zero_padding_ && __parse_zero_padding(__begin) && __begin == __end)
       return __begin;
 
-    if (__parse_width(__begin, __end, __parse_ctx) && __begin == __end)
+    if (__parse_width(__begin, __end, __ctx) && __begin == __end)
       return __begin;
 
-    if (__fields.__precision_ && __parse_precision(__begin, __end, __parse_ctx) && __begin == __end)
+    if (__fields.__precision_ && __parse_precision(__begin, __end, __ctx) && __begin == __end)
       return __begin;
 
     if (__fields.__locale_specific_form_ && __parse_locale_specific_form(__begin) && __begin == __end)
@@ -476,12 +475,12 @@
   }
 
   template <contiguous_iterator _Iterator>
-  _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_width(_Iterator& __begin, _Iterator __end, auto& __parse_ctx) {
+  _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_width(_Iterator& __begin, _Iterator __end, auto& __ctx) {
     if (*__begin == _CharT('0'))
       std::__throw_format_error("A format-spec width field shouldn't have a leading zero");
 
     if (*__begin == _CharT('{')) {
-      __format::__parse_number_result __r = __format_spec::__parse_arg_id(++__begin, __end, __parse_ctx);
+      __format::__parse_number_result __r = __format_spec::__parse_arg_id(++__begin, __end, __ctx);
       __width_as_arg_ = true;
       __width_ = __r.__value;
       __begin = __r.__last;
@@ -500,7 +499,7 @@
   }
 
   template <contiguous_iterator _Iterator>
-  _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_precision(_Iterator& __begin, _Iterator __end, auto& __parse_ctx) {
+  _LIBCPP_HIDE_FROM_ABI constexpr bool __parse_precision(_Iterator& __begin, _Iterator __end, auto& __ctx) {
     if (*__begin != _CharT('.'))
       return false;
 
@@ -509,7 +508,7 @@
       std::__throw_format_error("End of input while parsing format-spec precision");
 
     if (*__begin == _CharT('{')) {
-      __format::__parse_number_result __arg_id = __format_spec::__parse_arg_id(++__begin, __end, __parse_ctx);
+      __format::__parse_number_result __arg_id = __format_spec::__parse_arg_id(++__begin, __end, __ctx);
       __precision_as_arg_ = true;
       __precision_ = __arg_id.__value;
       __begin = __arg_id.__last;
diff --git a/libcxx/include/__format/range_formatter.h b/libcxx/include/__format/range_formatter.h
--- a/libcxx/include/__format/range_formatter.h
+++ b/libcxx/include/__format/range_formatter.h
@@ -54,15 +54,15 @@
   _LIBCPP_HIDE_FROM_ABI constexpr const formatter<_Tp, _CharT>& underlying() const noexcept { return __underlying_; }
 
   template <class _ParseContext>
-  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __parse_ctx) {
-    auto __begin = __parser_.__parse(__parse_ctx, __format_spec::__fields_range);
-    auto __end   = __parse_ctx.end();
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    auto __begin = __parser_.__parse(__ctx, __format_spec::__fields_range);
+    auto __end   = __ctx.end();
     // Note the cases where __begin == __end in this code only happens when the
     // replacement-field has no terminating }, or when the parse is manually
     // called with a format-spec. The former is an error and the latter means
     // using a formatter without the format functions or print.
     if (__begin == __end) [[unlikely]]
-      return __parse_empty_range_underlying_spec(__parse_ctx, __begin);
+      return __parse_empty_range_underlying_spec(__ctx, __begin);
 
     // The n field overrides a possible m type, therefore delay applying the
     // effect of n until the type has been procesed.
@@ -72,7 +72,7 @@
       if (__begin == __end) [[unlikely]] {
         // Since there is no more data, clear the brackets before returning.
         set_brackets({}, {});
-        return __parse_empty_range_underlying_spec(__parse_ctx, __begin);
+        return __parse_empty_range_underlying_spec(__ctx, __begin);
       }
     }
 
@@ -80,7 +80,7 @@
     if (__clear_brackets)
       set_brackets({}, {});
     if (__begin == __end) [[unlikely]]
-      return __parse_empty_range_underlying_spec(__parse_ctx, __begin);
+      return __parse_empty_range_underlying_spec(__ctx, __begin);
 
     bool __has_range_underlying_spec = *__begin == _CharT(':');
     if (__has_range_underlying_spec) {
@@ -95,8 +95,8 @@
       // get -} as input which my be valid.
       std::__throw_format_error("The format-spec should consume the input or end with a '}'");
 
-    __parse_ctx.advance_to(__begin);
-    __begin = __underlying_.parse(__parse_ctx);
+    __ctx.advance_to(__begin);
+    __begin = __underlying_.parse(__ctx);
 
     // This test should not be required if __has_range_underlying_spec is false.
     // However this test makes sure the underlying formatter left the parser in
@@ -260,9 +260,9 @@
 
   template <class _ParseContext>
   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator
-  __parse_empty_range_underlying_spec(_ParseContext& __parse_ctx, typename _ParseContext::iterator __begin) {
-    __parse_ctx.advance_to(__begin);
-    [[maybe_unused]] typename _ParseContext::iterator __result = __underlying_.parse(__parse_ctx);
+  __parse_empty_range_underlying_spec(_ParseContext& __ctx, typename _ParseContext::iterator __begin) {
+    __ctx.advance_to(__begin);
+    [[maybe_unused]] typename _ParseContext::iterator __result = __underlying_.parse(__ctx);
     _LIBCPP_ASSERT(__result == __begin,
                    "the underlying's parse function should not advance the input beyond the end of the input");
     return __begin;
diff --git a/libcxx/include/thread b/libcxx/include/thread
--- a/libcxx/include/thread
+++ b/libcxx/include/thread
@@ -240,12 +240,13 @@
 template <__fmt_char_type _CharT>
 struct _LIBCPP_TEMPLATE_VIS formatter<__thread_id, _CharT> {
   public:
-    _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
-        -> decltype(__parse_ctx.begin()) {
-        return __parser_.__parse(__parse_ctx, __format_spec::__fields_fill_align_width);
+    template <class _ParseContext>
+    _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+        return __parser_.__parse(__ctx, __format_spec::__fields_fill_align_width);
     }
 
-    _LIBCPP_HIDE_FROM_ABI auto format(__thread_id __id, auto& __ctx) const -> decltype(__ctx.out()) {
+    template <class _FormatContext>
+    _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator format(__thread_id __id, _FormatContext& __ctx) const {
         // In __threading_support __libcpp_thread_id is either a
         // unsigned long long or a pthread_t.
         //