diff --git a/libcxx/docs/ReleaseNotes/18.rst b/libcxx/docs/ReleaseNotes/18.rst
index 311a06e34c49d..14e1e09907fad 100644
--- a/libcxx/docs/ReleaseNotes/18.rst
+++ b/libcxx/docs/ReleaseNotes/18.rst
@@ -61,6 +61,7 @@ Implemented Papers
 - P1759R6 - Native handles and file streams
 - P2868R3 - Remove Deprecated ``std::allocator`` Typedef From C++26
 - P2517R1 - Add a conditional ``noexcept`` specification to ``std::apply``
+- P2637R3 - Member ``visit``
 - P2447R6 - ``span`` over initializer list
 
 
diff --git a/libcxx/docs/Status/Cxx2cPapers.csv b/libcxx/docs/Status/Cxx2cPapers.csv
index f6124d9a6c4e3..e49290b45589a 100644
--- a/libcxx/docs/Status/Cxx2cPapers.csv
+++ b/libcxx/docs/Status/Cxx2cPapers.csv
@@ -17,7 +17,7 @@
 "`P0792R14 <https://wg21.link/P0792R14>`__","LWG","``function_ref``: a type-erased callable reference","Varna June 2023","","",""
 "`P2874R2 <https://wg21.link/P2874R2>`__","LWG","Mandating Annex D Require No More","Varna June 2023","","",""
 "`P2757R3 <https://wg21.link/P2757R3>`__","LWG","Type-checking format args","Varna June 2023","","","|format|"
-"`P2637R3 <https://wg21.link/P2637R3>`__","LWG","Member ``visit``","Varna June 2023","|Partial|","18.0",""
+"`P2637R3 <https://wg21.link/P2637R3>`__","LWG","Member ``visit``","Varna June 2023","|Complete|","18.0",""
 "`P2641R4 <https://wg21.link/P2641R4>`__","CWG, LWG","Checking if a ``union`` alternative is active","Varna June 2023","","",""
 "`P1759R6 <https://wg21.link/P1759R6>`__","LWG","Native handles and file streams","Varna June 2023","|Complete|","18.0",""
 "`P2697R1 <https://wg21.link/P2697R1>`__","LWG","Interfacing ``bitset`` with ``string_view``","Varna June 2023","|Complete|","18.0",""
diff --git a/libcxx/docs/Status/FormatIssues.csv b/libcxx/docs/Status/FormatIssues.csv
index 513988d08036c..6e58e752191ea 100644
--- a/libcxx/docs/Status/FormatIssues.csv
+++ b/libcxx/docs/Status/FormatIssues.csv
@@ -16,7 +16,7 @@ Number,Name,Standard,Assignee,Status,First released version
 "`P2693R1 <https://wg21.link/P2693R1>`__","Formatting ``thread::id`` and ``stacktrace``","C++23","Mark de Wever","|In Progress|"
 "`P2510R3 <https://wg21.link/P2510R3>`__","Formatting pointers","C++26","Mark de Wever","|Complete|",17.0
 "`P2757R3 <https://wg21.link/P2757R3>`__","Type-checking format args","C++26","","",
-"`P2637R3 <https://wg21.link/P2637R3>`__","Member ``visit``","C++26","","",
+"`P2637R3 <https://wg21.link/P2637R3>`__","Member ``visit``","C++26","Hristo Hristov","|Complete|",18.0
 "`P2905R2 <https://wg21.link/P2905R2>`__","Runtime format strings","C++26 DR","Mark de Wever","|Complete|",18.0
 "`P2918R2 <https://wg21.link/P2918R2>`__","Runtime format strings II","C++26","Mark de Wever","|Complete|",18.0
 "`P2909R4 <https://wg21.link/P2909R4>`__","Fix formatting of code units as integers (Dude, where’s my ``char``?)","C++26 DR","Mark de Wever","|Complete|",18.0
diff --git a/libcxx/include/__config b/libcxx/include/__config
index 2825d03b7c205..639f88e21d274 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -984,6 +984,12 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_DEPRECATED_IN_CXX23
 #  endif
 
+#  if _LIBCPP_STD_VER >= 26
+#    define _LIBCPP_DEPRECATED_IN_CXX26 _LIBCPP_DEPRECATED
+#  else
+#    define _LIBCPP_DEPRECATED_IN_CXX26
+#  endif
+
 #  if !defined(_LIBCPP_HAS_NO_CHAR8_T)
 #    define _LIBCPP_DEPRECATED_WITH_CHAR8_T _LIBCPP_DEPRECATED
 #  else
diff --git a/libcxx/include/__format/format_arg.h b/libcxx/include/__format/format_arg.h
index 10fca15d5a7a9..02ee3cef7d402 100644
--- a/libcxx/include/__format/format_arg.h
+++ b/libcxx/include/__format/format_arg.h
@@ -93,7 +93,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr __arg_t __get_packed_type(uint64_t __types, size
 
 } // namespace __format
 
-// This function is not user obervable, so it can directly use the non-standard
+// This function is not user observable, so it can directly use the non-standard
 // types of the "variant". See __arg_t for more details.
 template <class _Visitor, class _Context>
 _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
@@ -144,6 +144,59 @@ _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_
   __libcpp_unreachable();
 }
 
+#  if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+
+template <class _Rp, class _Visitor, class _Context>
+_LIBCPP_HIDE_FROM_ABI _Rp __visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
+  switch (__arg.__type_) {
+  case __format::__arg_t::__none:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__monostate_);
+  case __format::__arg_t::__boolean:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__boolean_);
+  case __format::__arg_t::__char_type:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__char_type_);
+  case __format::__arg_t::__int:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__int_);
+  case __format::__arg_t::__long_long:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__long_long_);
+  case __format::__arg_t::__i128:
+#    ifndef _LIBCPP_HAS_NO_INT128
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__i128_);
+#    else
+    __libcpp_unreachable();
+#    endif
+  case __format::__arg_t::__unsigned:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__unsigned_);
+  case __format::__arg_t::__unsigned_long_long:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__unsigned_long_long_);
+  case __format::__arg_t::__u128:
+#    ifndef _LIBCPP_HAS_NO_INT128
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__u128_);
+#    else
+    __libcpp_unreachable();
+#    endif
+  case __format::__arg_t::__float:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__float_);
+  case __format::__arg_t::__double:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__double_);
+  case __format::__arg_t::__long_double:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__long_double_);
+  case __format::__arg_t::__const_char_type_ptr:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__const_char_type_ptr_);
+  case __format::__arg_t::__string_view:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__string_view_);
+  case __format::__arg_t::__ptr:
+    return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__ptr_);
+  case __format::__arg_t::__handle:
+    return std::invoke_r<_Rp>(
+        std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__arg.__value_.__handle_});
+  }
+
+  __libcpp_unreachable();
+}
+
+#  endif // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+
 /// Contains the values used in basic_format_arg.
 ///
 /// This is a separate type so it's possible to store the values and types in
@@ -227,6 +280,52 @@ class _LIBCPP_TEMPLATE_VIS basic_format_arg {
 
   _LIBCPP_HIDE_FROM_ABI explicit operator bool() const noexcept { return __type_ != __format::__arg_t::__none; }
 
+#  if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+
+  // This function is user facing, so it must wrap the non-standard types of
+  // the "variant" in a handle to stay conforming. See __arg_t for more details.
+  template <class _Visitor>
+  _LIBCPP_HIDE_FROM_ABI decltype(auto) visit(this basic_format_arg __arg, _Visitor&& __vis) {
+    switch (__arg.__type_) {
+#    ifndef _LIBCPP_HAS_NO_INT128
+    case __format::__arg_t::__i128: {
+      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
+      return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+    }
+
+    case __format::__arg_t::__u128: {
+      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
+      return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+    }
+#    endif
+    default:
+      return std::__visit_format_arg(std::forward<_Visitor>(__vis), __arg);
+    }
+  }
+
+  // This function is user facing, so it must wrap the non-standard types of
+  // the "variant" in a handle to stay conforming. See __arg_t for more details.
+  template <class _Rp, class _Visitor>
+  _LIBCPP_HIDE_FROM_ABI _Rp visit(this basic_format_arg __arg, _Visitor&& __vis) {
+    switch (__arg.__type_) {
+#    ifndef _LIBCPP_HAS_NO_INT128
+    case __format::__arg_t::__i128: {
+      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
+      return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+    }
+
+    case __format::__arg_t::__u128: {
+      typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
+      return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+    }
+#    endif
+    default:
+      return std::__visit_format_arg<_Rp>(std::forward<_Visitor>(__vis), __arg);
+    }
+  }
+
+#  endif // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+
 private:
   using char_type = typename _Context::char_type;
 
@@ -267,7 +366,11 @@ class _LIBCPP_TEMPLATE_VIS basic_format_arg<_Context>::handle {
 // This function is user facing, so it must wrap the non-standard types of
 // the "variant" in a handle to stay conforming. See __arg_t for more details.
 template <class _Visitor, class _Context>
-_LIBCPP_HIDE_FROM_ABI decltype(auto) visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
+#  if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+_LIBCPP_DEPRECATED_IN_CXX26
+#  endif
+    _LIBCPP_HIDE_FROM_ABI decltype(auto)
+    visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
   switch (__arg.__type_) {
 #  ifndef _LIBCPP_HAS_NO_INT128
   case __format::__arg_t::__i128: {
@@ -279,7 +382,7 @@ _LIBCPP_HIDE_FROM_ABI decltype(auto) visit_format_arg(_Visitor&& __vis, basic_fo
     typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
     return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
   }
-#  endif
+#  endif // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
   default:
     return std::__visit_format_arg(std::forward<_Visitor>(__vis), __arg);
   }
diff --git a/libcxx/include/__format/format_context.h b/libcxx/include/__format/format_context.h
index 5b252b81f691b..0beaa84b028be 100644
--- a/libcxx/include/__format/format_context.h
+++ b/libcxx/include/__format/format_context.h
@@ -163,20 +163,25 @@ class _LIBCPP_TEMPLATE_VIS basic_format_context<typename __format::__retarget_bu
 #  endif
         __ctx_(std::addressof(__ctx)),
         __arg_([](void* __c, size_t __id) {
-          return std::visit_format_arg(
-              [&](auto __arg) -> basic_format_arg<basic_format_context> {
-                if constexpr (same_as<decltype(__arg), monostate>)
-                  return {};
-                else if constexpr (same_as<decltype(__arg), typename basic_format_arg<_Context>::handle>)
-                  // At the moment it's not possible for formatting to use a re-targeted handle.
-                  // TODO FMT add this when support is needed.
-                  std::__throw_format_error("Re-targeting handle not supported");
-                else
-                  return basic_format_arg<basic_format_context>{
-                      __format::__determine_arg_t<basic_format_context, decltype(__arg)>(),
-                      __basic_format_arg_value<basic_format_context>(__arg)};
-              },
-              static_cast<_Context*>(__c)->arg(__id));
+          auto __visitor = [&](auto __arg) -> basic_format_arg<basic_format_context> {
+            if constexpr (same_as<decltype(__arg), monostate>)
+              return {};
+            else if constexpr (same_as<decltype(__arg), typename basic_format_arg<_Context>::handle>)
+              // At the moment it's not possible for formatting to use a re-targeted handle.
+              // TODO FMT add this when support is needed.
+              std::__throw_format_error("Re-targeting handle not supported");
+            else
+              return basic_format_arg<basic_format_context>{
+                  __format::__determine_arg_t<basic_format_context, decltype(__arg)>(),
+                  __basic_format_arg_value<basic_format_context>(__arg)};
+          };
+#  if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+          return static_cast<_Context*>(__c)->arg(__id).visit(std::move(__visitor));
+#  else
+          _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+          return std::visit_format_arg(std::move(__visitor), static_cast<_Context*>(__c)->arg(__id));
+          _LIBCPP_SUPPRESS_DEPRECATED_POP
+#  endif // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
         }) {
   }
 
diff --git a/libcxx/include/format b/libcxx/include/format
index ab9b336d0cdab..64f6ba1d25284 100644
--- a/libcxx/include/format
+++ b/libcxx/include/format
@@ -170,7 +170,7 @@ namespace std {
   template<class Context> class basic_format_arg;
 
   template<class Visitor, class Context>
-    see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
+    see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg); // Deprecated in C++26
 
   // [format.arg.store], class template format-arg-store
   template<class Context, class... Args> struct format-arg-store;      // exposition only
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.pass.cpp
new file mode 100644
index 0000000000000..994ccc70a38da
--- /dev/null
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.pass.cpp
@@ -0,0 +1,333 @@
+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
+// UNSUPPORTED: GCC-ALWAYS_INLINE-FIXME
+// The tested functionality needs deducing this.
+// UNSUPPORTED: clang-16 || clang-17
+// XFAIL: apple-clang
+
+// <format>
+
+// class basic_format_arg;
+
+// template<class Visitor>
+//   decltype(auto) visit(this basic_format_arg arg, Visitor&& vis);  // since C++26
+
+#include <algorithm>
+#include <cassert>
+#include <format>
+#include <type_traits>
+
+#include "constexpr_char_traits.h"
+#include "make_string.h"
+#include "min_allocator.h"
+#include "test_macros.h"
+
+template <class Context, class To, class From>
+void test(From value) {
+  auto store = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  LIBCPP_ASSERT(format_args.__size() == 1);
+  assert(format_args.get(0));
+
+  auto result = format_args.get(0).visit([v = To(value)](auto a) -> To {
+    if constexpr (std::is_same_v<To, decltype(a)>) {
+      assert(v == a);
+      return a;
+    } else {
+      assert(false);
+      return {};
+    }
+  });
+
+  using ct = std::common_type_t<From, To>;
+  assert(static_cast<ct>(result) == static_cast<ct>(value));
+}
+
+// Some types, as an extension, are stored in the variant. The Standard
+// requires them to be observed as a handle.
+template <class Context, class T>
+void test_handle(T value) {
+  auto store = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  LIBCPP_ASSERT(format_args.__size() == 1);
+  assert(format_args.get(0));
+
+  format_args.get(0).visit([](auto a) {
+    assert((std::is_same_v<decltype(a), typename std::basic_format_arg<Context>::handle>));
+  });
+}
+
+// Test specific for string and string_view.
+//
+// Since both result in a string_view there's no need to pass this as a
+// template argument.
+template <class Context, class From>
+void test_string_view(From value) {
+  auto store = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  LIBCPP_ASSERT(format_args.__size() == 1);
+  assert(format_args.get(0));
+
+  using CharT = typename Context::char_type;
+  using To    = std::basic_string_view<CharT>;
+  using V     = std::basic_string<CharT>;
+
+  auto result = format_args.get(0).visit([v = V(value.begin(), value.end())](auto a) -> To {
+    if constexpr (std::is_same_v<To, decltype(a)>) {
+      assert(v == a);
+      return a;
+    } else {
+      assert(false);
+      return {};
+    }
+  });
+
+  assert(std::equal(value.begin(), value.end(), result.begin(), result.end()));
+}
+
+template <class CharT>
+void test() {
+  using Context = std::basic_format_context<CharT*, CharT>;
+  std::basic_string<CharT> empty;
+  std::basic_string<CharT> str = MAKE_STRING(CharT, "abc");
+
+  // Test boolean types.
+
+  test<Context, bool>(true);
+  test<Context, bool>(false);
+
+  // Test CharT types.
+
+  test<Context, CharT, CharT>('a');
+  test<Context, CharT, CharT>('z');
+  test<Context, CharT, CharT>('0');
+  test<Context, CharT, CharT>('9');
+
+  // Test char types.
+
+  if (std::is_same_v<CharT, char>) {
+    // char to char -> char
+    test<Context, CharT, char>('a');
+    test<Context, CharT, char>('z');
+    test<Context, CharT, char>('0');
+    test<Context, CharT, char>('9');
+  } else {
+    if (std::is_same_v<CharT, wchar_t>) {
+      // char to wchar_t -> wchar_t
+      test<Context, wchar_t, char>('a');
+      test<Context, wchar_t, char>('z');
+      test<Context, wchar_t, char>('0');
+      test<Context, wchar_t, char>('9');
+    } else if (std::is_signed_v<char>) {
+      // char to CharT -> int
+      // This happens when CharT is a char8_t, char16_t, or char32_t and char
+      // is a signed type.
+      // Note if sizeof(CharT) > sizeof(int) this test fails. If there are
+      // platforms where that occurs extra tests need to be added for char32_t
+      // testing it against a long long.
+      test<Context, int, char>('a');
+      test<Context, int, char>('z');
+      test<Context, int, char>('0');
+      test<Context, int, char>('9');
+    } else {
+      // char to CharT -> unsigned
+      // This happens when CharT is a char8_t, char16_t, or char32_t and char
+      // is an unsigned type.
+      // Note if sizeof(CharT) > sizeof(unsigned) this test fails. If there are
+      // platforms where that occurs extra tests need to be added for char32_t
+      // testing it against an unsigned long long.
+      test<Context, unsigned, char>('a');
+      test<Context, unsigned, char>('z');
+      test<Context, unsigned, char>('0');
+      test<Context, unsigned, char>('9');
+    }
+  }
+
+  // Test signed integer types.
+
+  test<Context, int, signed char>(std::numeric_limits<signed char>::min());
+  test<Context, int, signed char>(0);
+  test<Context, int, signed char>(std::numeric_limits<signed char>::max());
+
+  test<Context, int, short>(std::numeric_limits<short>::min());
+  test<Context, int, short>(std::numeric_limits<signed char>::min());
+  test<Context, int, short>(0);
+  test<Context, int, short>(std::numeric_limits<signed char>::max());
+  test<Context, int, short>(std::numeric_limits<short>::max());
+
+  test<Context, int, int>(std::numeric_limits<int>::min());
+  test<Context, int, int>(std::numeric_limits<short>::min());
+  test<Context, int, int>(std::numeric_limits<signed char>::min());
+  test<Context, int, int>(0);
+  test<Context, int, int>(std::numeric_limits<signed char>::max());
+  test<Context, int, int>(std::numeric_limits<short>::max());
+  test<Context, int, int>(std::numeric_limits<int>::max());
+
+  using LongToType = std::conditional_t<sizeof(long) == sizeof(int), int, long long>;
+
+  test<Context, LongToType, long>(std::numeric_limits<long>::min());
+  test<Context, LongToType, long>(std::numeric_limits<int>::min());
+  test<Context, LongToType, long>(std::numeric_limits<short>::min());
+  test<Context, LongToType, long>(std::numeric_limits<signed char>::min());
+  test<Context, LongToType, long>(0);
+  test<Context, LongToType, long>(std::numeric_limits<signed char>::max());
+  test<Context, LongToType, long>(std::numeric_limits<short>::max());
+  test<Context, LongToType, long>(std::numeric_limits<int>::max());
+  test<Context, LongToType, long>(std::numeric_limits<long>::max());
+
+  test<Context, long long, long long>(std::numeric_limits<long long>::min());
+  test<Context, long long, long long>(std::numeric_limits<long>::min());
+  test<Context, long long, long long>(std::numeric_limits<int>::min());
+  test<Context, long long, long long>(std::numeric_limits<short>::min());
+  test<Context, long long, long long>(std::numeric_limits<signed char>::min());
+  test<Context, long long, long long>(0);
+  test<Context, long long, long long>(std::numeric_limits<signed char>::max());
+  test<Context, long long, long long>(std::numeric_limits<short>::max());
+  test<Context, long long, long long>(std::numeric_limits<int>::max());
+  test<Context, long long, long long>(std::numeric_limits<long>::max());
+  test<Context, long long, long long>(std::numeric_limits<long long>::max());
+
+#ifndef TEST_HAS_NO_INT128
+  test_handle<Context, __int128_t>(0);
+#endif // TEST_HAS_NO_INT128
+
+  // Test unsigned integer types.
+
+  test<Context, unsigned, unsigned char>(0);
+  test<Context, unsigned, unsigned char>(std::numeric_limits<unsigned char>::max());
+
+  test<Context, unsigned, unsigned short>(0);
+  test<Context, unsigned, unsigned short>(std::numeric_limits<unsigned char>::max());
+  test<Context, unsigned, unsigned short>(std::numeric_limits<unsigned short>::max());
+
+  test<Context, unsigned, unsigned>(0);
+  test<Context, unsigned, unsigned>(std::numeric_limits<unsigned char>::max());
+  test<Context, unsigned, unsigned>(std::numeric_limits<unsigned short>::max());
+  test<Context, unsigned, unsigned>(std::numeric_limits<unsigned>::max());
+
+  using UnsignedLongToType =
+      std::conditional_t<sizeof(unsigned long) == sizeof(unsigned), unsigned, unsigned long long>;
+
+  test<Context, UnsignedLongToType, unsigned long>(0);
+  test<Context, UnsignedLongToType, unsigned long>(std::numeric_limits<unsigned char>::max());
+  test<Context, UnsignedLongToType, unsigned long>(std::numeric_limits<unsigned short>::max());
+  test<Context, UnsignedLongToType, unsigned long>(std::numeric_limits<unsigned>::max());
+  test<Context, UnsignedLongToType, unsigned long>(std::numeric_limits<unsigned long>::max());
+
+  test<Context, unsigned long long, unsigned long long>(0);
+  test<Context, unsigned long long, unsigned long long>(std::numeric_limits<unsigned char>::max());
+  test<Context, unsigned long long, unsigned long long>(std::numeric_limits<unsigned short>::max());
+  test<Context, unsigned long long, unsigned long long>(std::numeric_limits<unsigned>::max());
+  test<Context, unsigned long long, unsigned long long>(std::numeric_limits<unsigned long>::max());
+  test<Context, unsigned long long, unsigned long long>(std::numeric_limits<unsigned long long>::max());
+
+#ifndef TEST_HAS_NO_INT128
+  test_handle<Context, __uint128_t>(0);
+#endif // TEST_HAS_NO_INT128
+
+  // Test floating point types.
+
+  test<Context, float, float>(-std::numeric_limits<float>::max());
+  test<Context, float, float>(-std::numeric_limits<float>::min());
+  test<Context, float, float>(-0.0);
+  test<Context, float, float>(0.0);
+  test<Context, float, float>(std::numeric_limits<float>::min());
+  test<Context, float, float>(std::numeric_limits<float>::max());
+
+  test<Context, double, double>(-std::numeric_limits<double>::max());
+  test<Context, double, double>(-std::numeric_limits<double>::min());
+  test<Context, double, double>(-0.0);
+  test<Context, double, double>(0.0);
+  test<Context, double, double>(std::numeric_limits<double>::min());
+  test<Context, double, double>(std::numeric_limits<double>::max());
+
+  test<Context, long double, long double>(-std::numeric_limits<long double>::max());
+  test<Context, long double, long double>(-std::numeric_limits<long double>::min());
+  test<Context, long double, long double>(-0.0);
+  test<Context, long double, long double>(0.0);
+  test<Context, long double, long double>(std::numeric_limits<long double>::min());
+  test<Context, long double, long double>(std::numeric_limits<long double>::max());
+
+  // Test const CharT pointer types.
+
+  test<Context, const CharT*, const CharT*>(empty.c_str());
+  test<Context, const CharT*, const CharT*>(str.c_str());
+
+  // Test string_view types.
+
+  {
+    using From = std::basic_string_view<CharT>;
+
+    test_string_view<Context>(From());
+    test_string_view<Context>(From(empty.c_str()));
+    test_string_view<Context>(From(str.c_str()));
+  }
+
+  {
+    using From = std::basic_string_view<CharT, constexpr_char_traits<CharT>>;
+
+    test_string_view<Context>(From());
+    test_string_view<Context>(From(empty.c_str()));
+    test_string_view<Context>(From(str.c_str()));
+  }
+
+  // Test string types.
+
+  {
+    using From = std::basic_string<CharT>;
+
+    test_string_view<Context>(From());
+    test_string_view<Context>(From(empty.c_str()));
+    test_string_view<Context>(From(str.c_str()));
+  }
+
+  {
+    using From = std::basic_string<CharT, constexpr_char_traits<CharT>, std::allocator<CharT>>;
+
+    test_string_view<Context>(From());
+    test_string_view<Context>(From(empty.c_str()));
+    test_string_view<Context>(From(str.c_str()));
+  }
+
+  {
+    using From = std::basic_string<CharT, std::char_traits<CharT>, min_allocator<CharT>>;
+
+    test_string_view<Context>(From());
+    test_string_view<Context>(From(empty.c_str()));
+    test_string_view<Context>(From(str.c_str()));
+  }
+
+  {
+    using From = std::basic_string<CharT, constexpr_char_traits<CharT>, min_allocator<CharT>>;
+
+    test_string_view<Context>(From());
+    test_string_view<Context>(From(empty.c_str()));
+    test_string_view<Context>(From(str.c_str()));
+  }
+
+  // Test pointer types.
+
+  test<Context, const void*>(nullptr);
+  int i = 0;
+  test<Context, const void*>(static_cast<void*>(&i));
+  const int ci = 0;
+  test<Context, const void*>(static_cast<const void*>(&ci));
+}
+
+int main(int, char**) {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+
+  return 0;
+}
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp
new file mode 100644
index 0000000000000..473278b7b4434
--- /dev/null
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp
@@ -0,0 +1,369 @@
+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
+// UNSUPPORTED: GCC-ALWAYS_INLINE-FIXME
+// The tested functionality needs deducing this.
+// UNSUPPORTED: clang-16 || clang-17
+// XFAIL: apple-clang
+
+// <format>
+
+// class basic_format_arg;
+
+// template<class R, class Visitor>
+//   R visit(this basic_format_arg arg, Visitor&& vis);
+
+#include <algorithm>
+#include <cassert>
+#include <format>
+#include <type_traits>
+
+#include "constexpr_char_traits.h"
+#include "make_string.h"
+#include "min_allocator.h"
+#include "test_macros.h"
+
+// The expected result type shouldn't matter,therefore use a hardcoded value for simplicity.
+using ExpectedResultType = bool;
+constexpr ExpectedResultType visited{true};
+
+template <class ExpectedR>
+ExpectedR make_expected_result() {
+  if constexpr (std::is_same_v<ExpectedR, bool>) {
+    return true;
+  } else if constexpr (std::is_same_v<ExpectedR, long>) {
+    return 192812079084L;
+  } else {
+    return "visited";
+  }
+}
+
+template <class Context, class To, class ExpectedR, class From>
+void test(From value, const ExpectedR& expectedValue) {
+  auto store = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  LIBCPP_ASSERT(format_args.__size() == 1);
+  assert(format_args.get(0));
+
+  // member
+  {
+    std::same_as<ExpectedR> decltype(auto) result =
+        format_args.get(0).template visit<ExpectedR>([v = To(value)](auto a) -> ExpectedR {
+          if constexpr (std::is_same_v<To, decltype(a)>) {
+            assert(v == a);
+            return make_expected_result<ExpectedR>();
+          } else {
+            assert(false);
+            return {};
+          }
+        });
+
+    assert(result == expectedValue);
+  }
+}
+
+// Some types, as an extension, are stored in the variant. The Standard
+// requires them to be observed as a handle.
+template <class Context, class T, class ExpectedR>
+void test_handle(T value, ExpectedR expectedValue) {
+  auto store = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  LIBCPP_ASSERT(format_args.__size() == 1);
+  assert(format_args.get(0));
+
+  std::same_as<ExpectedR> decltype(auto) result = format_args.get(0).template visit<ExpectedR>([](auto a) -> ExpectedR {
+    assert((std::is_same_v<decltype(a), typename std::basic_format_arg<Context>::handle>));
+
+    return make_expected_result<ExpectedR>();
+  });
+
+  assert(result == expectedValue);
+}
+
+// Test specific for string and string_view.
+//
+// Since both result in a string_view there's no need to pass this as a
+// template argument.
+template <class Context, class ExpectedR, class From>
+void test_string_view(From value, ExpectedR expectedValue) {
+  auto store = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  LIBCPP_ASSERT(format_args.__size() == 1);
+  assert(format_args.get(0));
+
+  using CharT = typename Context::char_type;
+  using To    = std::basic_string_view<CharT>;
+  using V     = std::basic_string<CharT>;
+
+  std::same_as<ExpectedR> decltype(auto) result =
+      format_args.get(0).template visit<ExpectedR>([v = V(value.begin(), value.end())](auto a) -> ExpectedR {
+        if constexpr (std::is_same_v<To, decltype(a)>) {
+          assert(v == a);
+          return make_expected_result<ExpectedR>();
+        } else {
+          assert(false);
+          return {};
+        }
+      });
+
+  assert(result == expectedValue);
+}
+
+template <class CharT>
+void test() {
+  using Context = std::basic_format_context<CharT*, CharT>;
+  std::basic_string<CharT> empty;
+  std::basic_string<CharT> str = MAKE_STRING(CharT, "abc");
+
+  // Test boolean types.
+
+  test<Context, bool, ExpectedResultType>(true, visited);
+  test<Context, bool, ExpectedResultType>(false, visited);
+
+  test<Context, bool, std::string>(true, "visited");
+  test<Context, bool, std::string>(false, "visited");
+
+  test<Context, bool, long>(true, 192812079084L);
+  test<Context, bool, long>(false, 192812079084L);
+
+  // Test CharT types.
+
+  test<Context, CharT, ExpectedResultType, CharT>('a', visited);
+  test<Context, CharT, ExpectedResultType, CharT>('z', visited);
+  test<Context, CharT, ExpectedResultType, CharT>('0', visited);
+  test<Context, CharT, ExpectedResultType, CharT>('9', visited);
+
+  // Test char types.
+
+  if (std::is_same_v<CharT, char>) {
+    // char to char -> char
+    test<Context, CharT, ExpectedResultType, char>('a', visited);
+    test<Context, CharT, ExpectedResultType, char>('z', visited);
+    test<Context, CharT, ExpectedResultType, char>('0', visited);
+    test<Context, CharT, ExpectedResultType, char>('9', visited);
+  } else {
+    if (std::is_same_v<CharT, wchar_t>) {
+      // char to wchar_t -> wchar_t
+      test<Context, wchar_t, ExpectedResultType, char>('a', visited);
+      test<Context, wchar_t, ExpectedResultType, char>('z', visited);
+      test<Context, wchar_t, ExpectedResultType, char>('0', visited);
+      test<Context, wchar_t, ExpectedResultType, char>('9', visited);
+    } else if (std::is_signed_v<char>) {
+      // char to CharT -> int
+      // This happens when CharT is a char8_t, char16_t, or char32_t and char
+      // is a signed type.
+      // Note if sizeof(CharT) > sizeof(int) this test fails. If there are
+      // platforms where that occurs extra tests need to be added for char32_t
+      // testing it against a long long.
+      test<Context, int, ExpectedResultType, char>('a', visited);
+      test<Context, int, ExpectedResultType, char>('z', visited);
+      test<Context, int, ExpectedResultType, char>('0', visited);
+      test<Context, int, ExpectedResultType, char>('9', visited);
+    } else {
+      // char to CharT -> unsigned
+      // This happens when CharT is a char8_t, char16_t, or char32_t and char
+      // is an unsigned type.
+      // Note if sizeof(CharT) > sizeof(unsigned) this test fails. If there are
+      // platforms where that occurs extra tests need to be added for char32_t
+      // testing it against an unsigned long long.
+      test<Context, unsigned, ExpectedResultType, char>('a', visited);
+      test<Context, unsigned, ExpectedResultType, char>('z', visited);
+      test<Context, unsigned, ExpectedResultType, char>('0', visited);
+      test<Context, unsigned, ExpectedResultType, char>('9', visited);
+    }
+  }
+
+  // Test signed integer types.
+
+  test<Context, int, ExpectedResultType, signed char>(std::numeric_limits<signed char>::min(), visited);
+  test<Context, int, ExpectedResultType, signed char>(0, visited);
+  test<Context, int, ExpectedResultType, signed char>(std::numeric_limits<signed char>::max(), visited);
+
+  test<Context, int, ExpectedResultType, short>(std::numeric_limits<short>::min(), visited);
+  test<Context, int, ExpectedResultType, short>(std::numeric_limits<signed char>::min(), visited);
+  test<Context, int, ExpectedResultType, short>(0, visited);
+  test<Context, int, ExpectedResultType, short>(std::numeric_limits<signed char>::max(), visited);
+  test<Context, int, ExpectedResultType, short>(std::numeric_limits<short>::max(), visited);
+
+  test<Context, int, ExpectedResultType, int>(std::numeric_limits<int>::min(), visited);
+  test<Context, int, ExpectedResultType, int>(std::numeric_limits<short>::min(), visited);
+  test<Context, int, ExpectedResultType, int>(std::numeric_limits<signed char>::min(), visited);
+  test<Context, int, ExpectedResultType, int>(0, visited);
+  test<Context, int, ExpectedResultType, int>(std::numeric_limits<signed char>::max(), visited);
+  test<Context, int, ExpectedResultType, int>(std::numeric_limits<short>::max(), visited);
+  test<Context, int, ExpectedResultType, int>(std::numeric_limits<int>::max(), visited);
+
+  using LongToType = std::conditional_t<sizeof(long) == sizeof(int), int, long long>;
+
+  test<Context, LongToType, ExpectedResultType, long>(std::numeric_limits<long>::min(), visited);
+  test<Context, LongToType, ExpectedResultType, long>(std::numeric_limits<int>::min(), visited);
+  test<Context, LongToType, ExpectedResultType, long>(std::numeric_limits<short>::min(), visited);
+  test<Context, LongToType, ExpectedResultType, long>(std::numeric_limits<signed char>::min(), visited);
+  test<Context, LongToType, ExpectedResultType, long>(0, visited);
+  test<Context, LongToType, ExpectedResultType, long>(std::numeric_limits<signed char>::max(), visited);
+  test<Context, LongToType, ExpectedResultType, long>(std::numeric_limits<short>::max(), visited);
+  test<Context, LongToType, ExpectedResultType, long>(std::numeric_limits<int>::max(), visited);
+  test<Context, LongToType, ExpectedResultType, long>(std::numeric_limits<long>::max(), visited);
+
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<long long>::min(), visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<long>::min(), visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<int>::min(), visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<short>::min(), visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<signed char>::min(), visited);
+  test<Context, long long, ExpectedResultType, long long>(0, visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<signed char>::max(), visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<short>::max(), visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<int>::max(), visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<long>::max(), visited);
+  test<Context, long long, ExpectedResultType, long long>(std::numeric_limits<long long>::max(), visited);
+
+#ifndef TEST_HAS_NO_INT128
+  test_handle<Context, __int128_t, ExpectedResultType>(0, visited);
+#endif // TEST_HAS_NO_INT128
+
+  // Test unsigned integer types.
+
+  test<Context, unsigned, ExpectedResultType, unsigned char>(0, visited);
+  test<Context, unsigned, ExpectedResultType, unsigned char>(std::numeric_limits<unsigned char>::max(), visited);
+
+  test<Context, unsigned, ExpectedResultType, unsigned short>(0, visited);
+  test<Context, unsigned, ExpectedResultType, unsigned short>(std::numeric_limits<unsigned char>::max(), visited);
+  test<Context, unsigned, ExpectedResultType, unsigned short>(std::numeric_limits<unsigned short>::max(), visited);
+
+  test<Context, unsigned, ExpectedResultType, unsigned>(0, visited);
+  test<Context, unsigned, ExpectedResultType, unsigned>(std::numeric_limits<unsigned char>::max(), visited);
+  test<Context, unsigned, ExpectedResultType, unsigned>(std::numeric_limits<unsigned short>::max(), visited);
+  test<Context, unsigned, ExpectedResultType, unsigned>(std::numeric_limits<unsigned>::max(), visited);
+
+  using UnsignedLongToType =
+      std::conditional_t<sizeof(unsigned long) == sizeof(unsigned), unsigned, unsigned long long>;
+
+  test<Context, UnsignedLongToType, ExpectedResultType, unsigned long>(0, visited);
+  test<Context, UnsignedLongToType, ExpectedResultType, unsigned long>(
+      std::numeric_limits<unsigned char>::max(), visited);
+  test<Context, UnsignedLongToType, ExpectedResultType, unsigned long>(
+      std::numeric_limits<unsigned short>::max(), visited);
+  test<Context, UnsignedLongToType, ExpectedResultType, unsigned long>(std::numeric_limits<unsigned>::max(), visited);
+  test<Context, UnsignedLongToType, ExpectedResultType, unsigned long>(
+      std::numeric_limits<unsigned long>::max(), visited);
+
+  test<Context, unsigned long long, ExpectedResultType, unsigned long long>(0, visited);
+  test<Context, unsigned long long, ExpectedResultType, unsigned long long>(
+      std::numeric_limits<unsigned char>::max(), visited);
+  test<Context, unsigned long long, ExpectedResultType, unsigned long long>(
+      std::numeric_limits<unsigned short>::max(), visited);
+  test<Context, unsigned long long, ExpectedResultType, unsigned long long>(
+      std::numeric_limits<unsigned>::max(), visited);
+  test<Context, unsigned long long, ExpectedResultType, unsigned long long>(
+      std::numeric_limits<unsigned long>::max(), visited);
+  test<Context, unsigned long long, ExpectedResultType, unsigned long long>(
+      std::numeric_limits<unsigned long long>::max(), visited);
+
+#ifndef TEST_HAS_NO_INT128
+  test_handle<Context, __uint128_t, ExpectedResultType>(0, visited);
+#endif // TEST_HAS_NO_INT128
+
+  // Test floating point types.
+
+  test<Context, float, ExpectedResultType, float>(-std::numeric_limits<float>::max(), visited);
+  test<Context, float, ExpectedResultType, float>(-std::numeric_limits<float>::min(), visited);
+  test<Context, float, ExpectedResultType, float>(-0.0, visited);
+  test<Context, float, ExpectedResultType, float>(0.0, visited);
+  test<Context, float, ExpectedResultType, float>(std::numeric_limits<float>::min(), visited);
+  test<Context, float, ExpectedResultType, float>(std::numeric_limits<float>::max(), visited);
+
+  test<Context, double, ExpectedResultType, double>(-std::numeric_limits<double>::max(), visited);
+  test<Context, double, ExpectedResultType, double>(-std::numeric_limits<double>::min(), visited);
+  test<Context, double, ExpectedResultType, double>(-0.0, visited);
+  test<Context, double, ExpectedResultType, double>(0.0, visited);
+  test<Context, double, ExpectedResultType, double>(std::numeric_limits<double>::min(), visited);
+  test<Context, double, ExpectedResultType, double>(std::numeric_limits<double>::max(), visited);
+
+  test<Context, long double, ExpectedResultType, long double>(-std::numeric_limits<long double>::max(), visited);
+  test<Context, long double, ExpectedResultType, long double>(-std::numeric_limits<long double>::min(), visited);
+  test<Context, long double, ExpectedResultType, long double>(-0.0, visited);
+  test<Context, long double, ExpectedResultType, long double>(0.0, visited);
+  test<Context, long double, ExpectedResultType, long double>(std::numeric_limits<long double>::min(), visited);
+  test<Context, long double, ExpectedResultType, long double>(std::numeric_limits<long double>::max(), visited);
+
+  // Test const CharT pointer types.
+
+  test<Context, const CharT*, ExpectedResultType, const CharT*>(empty.c_str(), visited);
+  test<Context, const CharT*, ExpectedResultType, const CharT*>(str.c_str(), visited);
+
+  // Test string_view types.
+
+  {
+    using From = std::basic_string_view<CharT>;
+
+    test_string_view<Context, ExpectedResultType>(From(), visited);
+    test_string_view<Context, ExpectedResultType>(From(empty.c_str()), visited);
+    test_string_view<Context, ExpectedResultType>(From(str.c_str()), visited);
+  }
+  {
+    using From = std::basic_string_view<CharT, constexpr_char_traits<CharT>>;
+
+    test_string_view<Context, ExpectedResultType>(From(), visited);
+    test_string_view<Context, ExpectedResultType>(From(empty.c_str()), visited);
+    test_string_view<Context, ExpectedResultType>(From(str.c_str()), visited);
+  }
+
+  // Test string types.
+
+  {
+    using From = std::basic_string<CharT>;
+
+    test_string_view<Context, ExpectedResultType>(From(), visited);
+    test_string_view<Context, ExpectedResultType>(From(empty.c_str()), visited);
+    test_string_view<Context, ExpectedResultType>(From(str.c_str()), visited);
+  }
+
+  {
+    using From = std::basic_string<CharT, constexpr_char_traits<CharT>, std::allocator<CharT>>;
+
+    test_string_view<Context, ExpectedResultType>(From(), visited);
+    test_string_view<Context, ExpectedResultType>(From(empty.c_str()), visited);
+    test_string_view<Context, ExpectedResultType>(From(str.c_str()), visited);
+  }
+
+  {
+    using From = std::basic_string<CharT, std::char_traits<CharT>, min_allocator<CharT>>;
+
+    test_string_view<Context, ExpectedResultType>(From(), visited);
+    test_string_view<Context, ExpectedResultType>(From(empty.c_str()), visited);
+    test_string_view<Context, ExpectedResultType>(From(str.c_str()), visited);
+  }
+
+  {
+    using From = std::basic_string<CharT, constexpr_char_traits<CharT>, min_allocator<CharT>>;
+
+    test_string_view<Context, ExpectedResultType>(From(), visited);
+    test_string_view<Context, ExpectedResultType>(From(empty.c_str()), visited);
+    test_string_view<Context, ExpectedResultType>(From(str.c_str()), visited);
+  }
+
+  // Test pointer types.
+
+  test<Context, const void*, ExpectedResultType>(nullptr, visited);
+  int i = 0;
+  test<Context, const void*, ExpectedResultType>(static_cast<void*>(&i), visited);
+  const int ci = 0;
+  test<Context, const void*, ExpectedResultType>(static_cast<const void*>(&ci), visited);
+}
+
+int main(int, char**) {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+
+  return 0;
+}
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.deprecated.verify.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.deprecated.verify.cpp
new file mode 100644
index 0000000000000..acd9228369e60
--- /dev/null
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.deprecated.verify.cpp
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
+// UNSUPPORTED: GCC-ALWAYS_INLINE-FIXME
+// UNSUPPORTED: clang-16 || clang-17
+// XFAIL: apple-clang
+
+// <format>
+
+// template<class Visitor, class Context>
+//   see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
+
+#include <format>
+#include <tuple>
+
+#include "test_macros.h"
+
+template <typename CharT, class To, class From>
+void test(From value) {
+  using Context = std::basic_format_context<CharT*, CharT>;
+  auto store    = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  // expected-warning-re@+1 1-2 {{std::basic_format_context{{.*}}' is deprecated}}
+  std::ignore = std::visit_format_arg([]([[maybe_unused]] auto a) -> To { return {}; }, format_args.get(0));
+}
+
+void test() {
+  test<char, bool>('a');
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t, bool>('a');
+#endif
+}
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp
index 3ddf2d0ff732a..3497d8935c8d6 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp
@@ -11,7 +11,7 @@
 // <format>
 
 // template<class Visitor, class Context>
-//   see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
+//   see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg); // Deprecated in C++26
 
 #include <algorithm>
 #include <format>
@@ -23,6 +23,10 @@
 #include "make_string.h"
 #include "min_allocator.h"
 
+#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+TEST_CLANG_DIAGNOSTIC_IGNORED("-Wdeprecated-declarations")
+#endif
+
 template <class Context, class To, class From>
 void test(From value) {
   auto store = std::make_format_args<Context>(value);
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
index 0f3931adf54df..a5d3703397f4e 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
@@ -24,14 +24,17 @@ void test(From value) {
   auto store = std::make_format_args<Context>(value);
   const std::basic_format_args<Context> format_args{store};
 
-  std::visit_format_arg(
-      [v = To(value)](auto a) {
-        if constexpr (std::is_same_v<To, decltype(a)>)
-          assert(v == a);
-        else
-          assert(false);
-      },
-      format_args.get(0));
+  auto visitor = [v = To(value)](auto a) {
+    if constexpr (std::is_same_v<To, decltype(a)>)
+      assert(v == a);
+    else
+      assert(false);
+  };
+#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+  format_args.get(0).visit(visitor);
+#else
+  std::visit_format_arg(visitor, format_args.get(0));
+#endif
 }
 
 // Some types, as an extension, are stored in the variant. The Standard
@@ -41,9 +44,12 @@ void test_handle(T value) {
   auto store = std::make_format_args<Context>(value);
   std::basic_format_args<Context> format_args{store};
 
-  std::visit_format_arg(
-      [](auto a) { assert((std::is_same_v<decltype(a), typename std::basic_format_arg<Context>::handle>)); },
-      format_args.get(0));
+  auto visitor = [](auto a) { assert((std::is_same_v<decltype(a), typename std::basic_format_arg<Context>::handle>)); };
+#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+  format_args.get(0).visit(visitor);
+#else
+  std::visit_format_arg(visitor, format_args.get(0));
+#endif
 }
 
 // Test specific for string and string_view.
@@ -58,14 +64,18 @@ void test_string_view(From value) {
   using CharT = typename Context::char_type;
   using To = std::basic_string_view<CharT>;
   using V = std::basic_string<CharT>;
-  std::visit_format_arg(
-      [v = V(value.begin(), value.end())](auto a) {
-        if constexpr (std::is_same_v<To, decltype(a)>)
-          assert(v == a);
-        else
-          assert(false);
-      },
-      format_args.get(0));
+
+  auto visitor = [v = V(value.begin(), value.end())](auto a) {
+    if constexpr (std::is_same_v<To, decltype(a)>)
+      assert(v == a);
+    else
+      assert(false);
+  };
+#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+  format_args.get(0).visit(visitor);
+#else
+  std::visit_format_arg(visitor, format_args.get(0));
+#endif
 }
 
 template <class CharT>
diff --git a/libcxx/test/support/test_basic_format_arg.h b/libcxx/test/support/test_basic_format_arg.h
index d8547d34b6db4..1ec719a48b6c8 100644
--- a/libcxx/test/support/test_basic_format_arg.h
+++ b/libcxx/test/support/test_basic_format_arg.h
@@ -7,18 +7,22 @@
 
 #include <concepts>
 #include <format>
+#include <utility>
 
 #include "test_macros.h"
 
 /// Returns whether the basic_format_arg contains a type T with the expected value.
 template <class Context, class T>
 bool test_basic_format_arg(std::basic_format_arg<Context> arg, T expected) {
-  return std::visit_format_arg(
-      [expected](auto a) {
-        if constexpr (std::same_as<decltype(a), T>)
-          return a == expected;
-        else
-          return false;
-      },
-      arg);
+  auto visitor = [expected](auto a) {
+    if constexpr (std::same_as<decltype(a), T>)
+      return a == expected;
+    else
+      return false;
+  };
+#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+  return arg.visit(std::move(visitor));
+#else
+  return std::visit_format_arg(std::move(visitor), arg);
+#endif
 }
diff --git a/libcxx/test/support/test_macros.h b/libcxx/test/support/test_macros.h
index fe68e13de6bcb..24f69c758f365 100644
--- a/libcxx/test/support/test_macros.h
+++ b/libcxx/test/support/test_macros.h
@@ -470,4 +470,9 @@ inline Tp const& DoNotOptimize(Tp const& value) {
 #  define TEST_IF_AIX(arg_true, arg_false) arg_false
 #endif
 
+// Clang-18 has support for deducing this, but it does not set the FTM.
+#ifdef _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  define TEST_HAS_EXPLICIT_THIS_PARAMETER
+#endif
+
 #endif // SUPPORT_TEST_MACROS_HPP
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index a5df187b046f6..667dd75278c8b 100755
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -467,6 +467,7 @@ def add_version_header(tc):
                 # "c++20": 202110 Not implemented P2372R3 Fixing locale handling in chrono formatters
                 "c++20": 202106,
                 # "c++23": 202207, Not implemented P2419R2 Clarify handling of encodings in localized formatting of chrono types
+                # "c++26": 202306, P2637R3 Member Visit (implemented)
                 # "c++26": 202311, P2918R2 Runtime format strings II (implemented)
             },
             # Note these three papers are adopted at the June 2023 meeting and have sequential numbering