diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -129,6 +129,7 @@
   __debug
   __errc
   __format/buffer.h
+  __format/enable_insertable.h
   __format/format_arg.h
   __format/format_args.h
   __format/format_context.h
diff --git a/libcxx/include/__format/buffer.h b/libcxx/include/__format/buffer.h
--- a/libcxx/include/__format/buffer.h
+++ b/libcxx/include/__format/buffer.h
@@ -11,9 +11,12 @@
 #define _LIBCPP___FORMAT_BUFFER_H
 
 #include <__config>
+#include <__format/enable_insertable.h>
 #include <__format/formatter.h> // for __char_type TODO FMT Move the concept?
+#include <__iterator/back_insert_iterator.h>
 #include <__iterator/concepts.h>
 #include <__utility/move.h>
+#include <array>
 #include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -95,6 +98,98 @@
   _OutIt __it_;
 };
 
+/// Concept to see whether a \a _Container is insertable.
+///
+/// The concept is used to validate whether multiple calls to a
+/// \ref back_insert_iterator can be replace by a call to \c _Container::insert.
+///
+/// \note a \a _Container needs to opt-in to the concept by specializing
+/// \ref __enable_insertable.
+template <class _Container>
+concept __insertable = __enable_insertable<_Container> &&
+    __formatter::__char_type<typename _Container::value_type> &&
+    requires(_Container& __t,
+             add_pointer_t<typename _Container::value_type> __first,
+             add_pointer_t<typename _Container::value_type> __last) {
+  __t.insert(__t.end(), __first, __last);
+};
+
+/// Extract the container type of a \ref back_insert_iterator.
+template <class _It>
+struct _LIBCPP_TEMPLATE_VIS __back_insert_iterator_container {
+  using type = void;
+};
+
+template <__insertable _Container>
+struct _LIBCPP_TEMPLATE_VIS
+    __back_insert_iterator_container<back_insert_iterator<_Container>> {
+  using type = _Container;
+};
+
+/// Helper to get the container of a \ref back_insert_iterator.
+template <class _Container>
+class _LIBCPP_TEMPLATE_VIS __container_extractor
+    : private back_insert_iterator<_Container> {
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit __container_extractor(
+      back_insert_iterator<_Container> __it)
+      : back_insert_iterator<_Container>(__it) {}
+
+  _LIBCPP_HIDE_FROM_ABI _Container* get() { return this->container; }
+};
+
+/// A buffer that wraps a \ref back_insert_iterator for a \a _Container.
+template <class _Container>
+class _LIBCPP_TEMPLATE_VIS __container_buffer {
+public:
+  using _CharT = typename _Container::value_type;
+
+  _LIBCPP_HIDE_FROM_ABI explicit __container_buffer(
+      back_insert_iterator<_Container> __it)
+      : __container_(__container_extractor<_Container>{__it}.get()) {}
+
+  _LIBCPP_HIDE_FROM_ABI void put(_CharT __c) {
+    *__buffer_it_++ = __c;
+    // Profiling showed flushing after adding is more efficient than flushing
+    // when entering the function.
+    if (__buffer_it_ == __buffer_.end())
+      __flush();
+  }
+
+  _LIBCPP_HIDE_FROM_ABI auto out() {
+    __flush();
+    return back_inserter(*__container_);
+  }
+
+private:
+  /// The size of the internal buffer.
+  ///
+  /// Profiling shows a 256 byte buffer seems optimal.
+  /// (256 elements for a char buffer and 64 elements for a 4-byte wchar_t)
+  static constexpr size_t __buffer_size = 256 / sizeof(_CharT);
+
+  array<_CharT, __buffer_size> __buffer_{};
+  _CharT* __buffer_it_{__buffer_.begin()};
+  _Container* __container_;
+
+  void __flush() {
+    // Use __buffer_it_ instead of end() since the buffer might be partly filled.
+    __container_->insert(__container_->end(), __buffer_.begin(), __buffer_it_);
+    __buffer_it_ = __buffer_.begin();
+  }
+};
+
+/// Selects the type of the buffer for the output iterator.
+template <class _OutIt, class _CharT>
+class _LIBCPP_TEMPLATE_VIS __buffer_selector {
+  using _Iterator = typename __back_insert_iterator_container<_OutIt>::type;
+
+public:
+  using type = conditional_t<same_as<_Iterator, void>,
+                             __iterator_wrapper_buffer<_OutIt, _CharT>,
+                             __container_buffer<_Iterator>>;
+};
+
 } // namespace __format
 
 #endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
diff --git a/libcxx/include/__format/enable_insertable.h b/libcxx/include/__format/enable_insertable.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__format/enable_insertable.h
@@ -0,0 +1,35 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___FORMAT_ENABLE_INSERTABLE_H
+#define _LIBCPP___FORMAT_ENABLE_INSERTABLE_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+namespace __format {
+
+/// Opt-in to enable \ref __insertable for a \a _Container.
+template <class _Container>
+inline constexpr bool __enable_insertable = false;
+
+} // namespace __format
+
+#endif //_LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORMAT_ENABLE_INSERTABLE_H
diff --git a/libcxx/include/deque b/libcxx/include/deque
--- a/libcxx/include/deque
+++ b/libcxx/include/deque
@@ -162,6 +162,7 @@
 
 #include <__config>
 #include <__debug>
+#include <__format/enable_insertable.h>
 #include <__split_buffer>
 #include <__utility/forward.h>
 #include <algorithm>
@@ -3018,6 +3019,20 @@
   __c.erase(_VSTD::remove_if(__c.begin(), __c.end(), __pred), __c.end());
   return __old_size - __c.size();
 }
+
+// TODO FMT Remove this once we require compilers with proper C++20 support.
+// If the compiler has no concepts support, the format header will be disabled.
+// Without concepts support enable_if needs to be used and that too much effort
+// to support compilers with partial C++20 support.
+# if !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+template <>
+inline constexpr bool __format::__enable_insertable<std::deque<char>> = true;
+template <>
+inline constexpr bool __format::__enable_insertable<std::deque<wchar_t>> = true;
+
+# endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
 #endif
 
 
diff --git a/libcxx/include/format b/libcxx/include/format
--- a/libcxx/include/format
+++ b/libcxx/include/format
@@ -267,6 +267,7 @@
 #include <__config>
 #include <__debug>
 #include <__format/buffer.h>
+#include <__format/enable_insertable.h>
 #include <__format/format_arg.h>
 #include <__format/format_args.h>
 #include <__format/format_context.h>
@@ -496,7 +497,7 @@
         _OutIt __out_it, basic_string_view<_CharT> __fmt,
         basic_format_args<basic_format_context<_FormatOutIt, _CharT>> __args) {
 
-  using _Buffer = __format::__iterator_wrapper_buffer<_OutIt, _CharT>;
+  using _Buffer = typename __format::__buffer_selector<_OutIt, _CharT>::type;
   _Buffer __buffer{_VSTD::move(__out_it)};
   _VSTD::__format::__vformat_to(
       basic_format_parse_context{__fmt, __args.__size()},
@@ -626,7 +627,7 @@
         _OutIt __out_it, locale __loc, basic_string_view<_CharT> __fmt,
         basic_format_args<basic_format_context<_FormatOutIt, _CharT>> __args) {
 
-  using _Buffer = __format::__iterator_wrapper_buffer<_OutIt, _CharT>;
+  using _Buffer = typename __format::__buffer_selector<_OutIt, _CharT>::type;
   _Buffer __buffer{_VSTD::move(__out_it)};
   _VSTD::__format::__vformat_to(
       basic_format_parse_context{__fmt, __args.__size()},
diff --git a/libcxx/include/list b/libcxx/include/list
--- a/libcxx/include/list
+++ b/libcxx/include/list
@@ -182,6 +182,7 @@
 
 #include <__config>
 #include <__debug>
+#include <__format/enable_insertable.h>
 #include <__utility/forward.h>
 #include <algorithm>
 #include <initializer_list>
@@ -2485,6 +2486,20 @@
 erase(list<_Tp, _Allocator>& __c, const _Up& __v) {
   return _VSTD::erase_if(__c, [&](auto& __elem) { return __elem == __v; });
 }
+
+// TODO FMT Remove this once we require compilers with proper C++20 support.
+// If the compiler has no concepts support, the format header will be disabled.
+// Without concepts support enable_if needs to be used and that too much effort
+// to support compilers with partial C++20 support.
+# if !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+template <>
+inline constexpr bool __format::__enable_insertable<std::list<char>> = true;
+template <>
+inline constexpr bool __format::__enable_insertable<std::list<wchar_t>> = true;
+
+# endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -439,6 +439,7 @@
         export locale
       }
       module buffer                 { private header "__format/buffer.h"                 }
+      module enable_intertable      { private header "__format/enable_insertable.h"      }
       module format_error           { private header "__format/format_error.h"           }
       module format_fwd             { private header "__format/format_fwd.h"             }
       module format_parse_context   { private header "__format/format_parse_context.h"   }
diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -518,6 +518,7 @@
 #include <__config>
 #include <__debug>
 #include <__functional_base>
+#include <__format/enable_insertable.h>
 #include <__iterator/wrap_iter.h>
 #include <algorithm>
 #include <compare>
@@ -4578,6 +4579,23 @@
 }
 #endif
 
+#if _LIBCPP_STD_VER > 17
+
+// TODO FMT Remove this once we require compilers with proper C++20 support.
+// If the compiler has no concepts support, the format header will be disabled.
+// Without concepts support enable_if needs to be used and that too much effort
+// to support compilers with partial C++20 support.
+# if !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+template <>
+inline constexpr bool __format::__enable_insertable<std::basic_string<char>> = true;
+template <>
+inline constexpr bool __format::__enable_insertable<std::basic_string<wchar_t>> = true;
+
+# endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+#endif //_LIBCPP_STD_VER > 17
+
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
diff --git a/libcxx/include/vector b/libcxx/include/vector
--- a/libcxx/include/vector
+++ b/libcxx/include/vector
@@ -274,6 +274,7 @@
 #include <__config>
 #include <__bit_reference>
 #include <__debug>
+#include <__format/enable_insertable.h>
 #include <__functional_base>
 #include <__iterator/wrap_iter.h>
 #include <__split_buffer>
@@ -3429,6 +3430,23 @@
 }
 #endif
 
+#if _LIBCPP_STD_VER > 17
+
+// TODO FMT Remove this once we require compilers with proper C++20 support.
+// If the compiler has no concepts support, the format header will be disabled.
+// Without concepts support enable_if needs to be used and that too much effort
+// to support compilers with partial C++20 support.
+# if !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+template <>
+inline constexpr bool __format::__enable_insertable<std::vector<char>> = true;
+template <>
+inline constexpr bool __format::__enable_insertable<std::vector<wchar_t>> = true;
+
+# endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+#endif //_LIBCPP_STD_VER > 17
+
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
diff --git a/libcxx/test/libcxx/diagnostics/detail.headers/format/enable_insertable.module.verify.cpp b/libcxx/test/libcxx/diagnostics/detail.headers/format/enable_insertable.module.verify.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/detail.headers/format/enable_insertable.module.verify.cpp
@@ -0,0 +1,16 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__format/enable_insertable.h'}}
+#include <__format/enable_insertable.h>
diff --git a/libcxx/test/libcxx/utilities/format/enable_insertable.compile.pass.cpp b/libcxx/test/libcxx/utilities/format/enable_insertable.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/utilities/format/enable_insertable.compile.pass.cpp
@@ -0,0 +1,140 @@
+//===----------------------------------------------------------------------===//
+// 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
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: libcpp-has-no-incomplete-format
+
+// <format>
+
+#include <format>
+#include <array>
+#include <deque>
+#include <forward_list>
+#include <list>
+#include <map>
+#include <queue>
+#include <set>
+#include <span>
+#include <stack>
+#include <string>
+#include <string_view>
+
+#include "test_macros.h"
+
+template <class CharT>
+struct no_value_type {
+  using iterator = CharT*;
+  iterator end();
+  void insert(iterator, CharT*, CharT*);
+};
+
+template <class CharT>
+struct no_end {
+  using value_type = CharT;
+  using iterator = CharT*;
+  void insert(iterator, CharT*, CharT*);
+};
+
+template <class CharT>
+struct no_insert {
+  using value_type = CharT;
+  using iterator = CharT*;
+  iterator end();
+};
+
+template <class CharT>
+struct no_specialization {
+  using value_type = CharT;
+  using iterator = CharT*;
+  iterator end();
+  void insert(iterator, CharT*, CharT*);
+};
+
+template <class CharT>
+struct valid {
+  using value_type = CharT;
+  using iterator = CharT*;
+  iterator end();
+  void insert(iterator, CharT*, CharT*);
+};
+
+namespace std::__format {
+template <>
+inline constexpr bool __enable_insertable<no_value_type<char>> = true;
+template <>
+inline constexpr bool __enable_insertable<no_value_type<wchar_t>> = true;
+template <>
+inline constexpr bool __enable_insertable<no_end<char>> = true;
+template <>
+inline constexpr bool __enable_insertable<no_end<wchar_t>> = true;
+template <>
+inline constexpr bool __enable_insertable<no_insert<char>> = true;
+template <>
+inline constexpr bool __enable_insertable<no_insert<wchar_t>> = true;
+template <>
+inline constexpr bool __enable_insertable<valid<char>> = true;
+template <>
+inline constexpr bool __enable_insertable<valid<wchar_t>> = true;
+} // namespace std::__format
+
+static_assert(!std::__format::__insertable<no_value_type<char>>);
+static_assert(!std::__format::__insertable<no_value_type<wchar_t>>);
+static_assert(!std::__format::__insertable<no_end<char>>);
+static_assert(!std::__format::__insertable<no_end<wchar_t>>);
+static_assert(!std::__format::__insertable<no_insert<char>>);
+static_assert(!std::__format::__insertable<no_insert<wchar_t>>);
+static_assert(!std::__format::__insertable<no_specialization<char>>);
+static_assert(!std::__format::__insertable<no_specialization<wchar_t>>);
+static_assert(std::__format::__insertable<valid<char>>);
+static_assert(std::__format::__insertable<valid<wchar_t>>);
+
+namespace std::__format {
+template <>
+inline constexpr bool __enable_insertable<valid<signed char>> = true;
+template <>
+inline constexpr bool __enable_insertable<valid<unsigned char>> = true;
+} // namespace std::__format
+
+static_assert(!std::__format::__insertable<valid<signed char>>);
+static_assert(!std::__format::__insertable<valid<unsigned char>>);
+
+static_assert(std::__format::__insertable<std::string>);
+static_assert(std::__format::__insertable<std::wstring>);
+static_assert(!std::__format::__insertable<std::string_view>);
+static_assert(!std::__format::__insertable<std::wstring_view>);
+
+static_assert(!std::__format::__insertable<std::array<char, 1>>);
+static_assert(!std::__format::__insertable<std::array<wchar_t, 1>>);
+
+static_assert(std::__format::__insertable<std::vector<char>>);
+static_assert(std::__format::__insertable<std::vector<wchar_t>>);
+static_assert(std::__format::__insertable<std::deque<char>>);
+static_assert(std::__format::__insertable<std::deque<wchar_t>>);
+static_assert(!std::__format::__insertable<std::forward_list<char>>);
+static_assert(!std::__format::__insertable<std::forward_list<wchar_t>>);
+static_assert(std::__format::__insertable<std::list<char>>);
+static_assert(std::__format::__insertable<std::list<wchar_t>>);
+
+static_assert(!std::__format::__insertable<std::set<char>>);
+static_assert(!std::__format::__insertable<std::set<wchar_t>>);
+static_assert(!std::__format::__insertable<std::map<char, char>>);
+static_assert(!std::__format::__insertable<std::map<wchar_t, wchar_t>>);
+static_assert(!std::__format::__insertable<std::multiset<char>>);
+static_assert(!std::__format::__insertable<std::multiset<wchar_t>>);
+static_assert(!std::__format::__insertable<std::multimap<char, char>>);
+static_assert(!std::__format::__insertable<std::multimap<wchar_t, wchar_t>>);
+
+static_assert(!std::__format::__insertable<std::stack<char>>);
+static_assert(!std::__format::__insertable<std::stack<wchar_t>>);
+static_assert(!std::__format::__insertable<std::queue<char>>);
+static_assert(!std::__format::__insertable<std::queue<wchar_t>>);
+static_assert(!std::__format::__insertable<std::priority_queue<char>>);
+static_assert(!std::__format::__insertable<std::priority_queue<wchar_t>>);
+
+static_assert(!std::__format::__insertable<std::span<char>>);
+static_assert(!std::__format::__insertable<std::span<wchar_t>>);