diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -555,7 +555,6 @@
   __ranges/views.h
   __ranges/zip_view.h
   __split_buffer
-  __std_stream
   __string/char_traits.h
   __string/constexpr_c_functions.h
   __string/extern_template_lists.h
diff --git a/libcxx/include/libcxx.imp b/libcxx/include/libcxx.imp
--- a/libcxx/include/libcxx.imp
+++ b/libcxx/include/libcxx.imp
@@ -8,7 +8,6 @@
   { include: [ "<__node_handle>", "private", "<unordered_set>", "public" ] },
   { include: [ "<__split_buffer>", "private", "<deque>", "public" ] },
   { include: [ "<__split_buffer>", "private", "<vector>", "public" ] },
-  { include: [ "<__std_stream>", "private", "<iostream>", "public" ] },
   { include: [ "<__threading_support>", "private", "<atomic>", "public" ] },
   { include: [ "<__threading_support>", "private", "<mutex>", "public" ] },
   { include: [ "<__threading_support>", "private", "<semaphore>", "public" ] },
diff --git a/libcxx/include/memory b/libcxx/include/memory
--- a/libcxx/include/memory
+++ b/libcxx/include/memory
@@ -881,6 +881,7 @@
 #include <__config>
 #include <__memory/addressof.h>
 #include <__memory/align.h>
+#include <__memory/aligned_alloc.h>
 #include <__memory/allocate_at_least.h>
 #include <__memory/allocation_guard.h>
 #include <__memory/allocator.h>
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -1675,10 +1675,6 @@
   module __mutex_base        { private header "__mutex_base"        export * }
   module __node_handle       { private header "__node_handle"       export * }
   module __split_buffer      { private header "__split_buffer"      export * }
-  module __std_stream        {
-    @requires_LIBCXX_ENABLE_LOCALIZATION@
-    private header "__std_stream" export *
-  }
   module __threading_support {         header "__threading_support" export * }
   module __tree              {         header "__tree"              export * }
   module __undef_macros      {         header "__undef_macros"      export * }
diff --git a/libcxx/src/filesystem/operations.cpp b/libcxx/src/filesystem/operations.cpp
--- a/libcxx/src/filesystem/operations.cpp
+++ b/libcxx/src/filesystem/operations.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 #include <__assert>
-#include <__utility/unreachable.h>
 #include <array>
 #include <climits>
 #include <cstdlib>
@@ -15,6 +14,7 @@
 #include <iterator>
 #include <string_view>
 #include <type_traits>
+#include <utility>
 #include <vector>
 
 #include "filesystem_common.h"
diff --git a/libcxx/src/include/ryu/digit_table.h b/libcxx/src/include/ryu/digit_table.h
--- a/libcxx/src/include/ryu/digit_table.h
+++ b/libcxx/src/include/ryu/digit_table.h
@@ -39,8 +39,8 @@
 #ifndef _LIBCPP_SRC_INCLUDE_RYU_DIGIT_TABLE_H
 #define _LIBCPP_SRC_INCLUDE_RYU_DIGIT_TABLE_H
 
-#include <__charconv/tables.h>
 #include <__config>
+#include <charconv>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
diff --git a/libcxx/src/include/ryu/ryu.h b/libcxx/src/include/ryu/ryu.h
--- a/libcxx/src/include/ryu/ryu.h
+++ b/libcxx/src/include/ryu/ryu.h
@@ -44,13 +44,12 @@
 // Avoid formatting to keep the changes with the original code minimal.
 // clang-format off
 
-#include <__charconv/chars_format.h>
-#include <__charconv/to_chars_result.h>
 #include <__config>
 #include <__debug>
-#include <__errc>
+#include <charconv>
 #include <cstdint>
 #include <cstring>
+#include <system_error>
 #include <type_traits>
 
 #include "include/ryu/f2s.h"
diff --git a/libcxx/include/__std_stream b/libcxx/src/include/std_stream.h
rename from libcxx/include/__std_stream
rename to libcxx/src/include/std_stream.h
diff --git a/libcxx/src/include/to_chars_floating_point.h b/libcxx/src/include/to_chars_floating_point.h
--- a/libcxx/src/include/to_chars_floating_point.h
+++ b/libcxx/src/include/to_chars_floating_point.h
@@ -17,18 +17,14 @@
 // Avoid formatting to keep the changes with the original code minimal.
 // clang-format off
 
-#include <__algorithm/find.h>
-#include <__algorithm/find_if.h>
-#include <__algorithm/lower_bound.h>
-#include <__algorithm/min.h>
+#include <algorithm>
 #include <__assert>
 #include <__config>
-#include <__functional/operations.h>
-#include <__iterator/access.h>
-#include <__iterator/size.h>
 #include <bit>
 #include <cfloat>
 #include <climits>
+#include <functional>
+#include <iterator>
 
 #include "include/ryu/ryu.h"
 
diff --git a/libcxx/src/ios.cpp b/libcxx/src/ios.cpp
--- a/libcxx/src/ios.cpp
+++ b/libcxx/src/ios.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 #include <__config>
-#include <__locale>
 #include <algorithm>
 #include <ios>
 #include <limits>
diff --git a/libcxx/src/iostream.cpp b/libcxx/src/iostream.cpp
--- a/libcxx/src/iostream.cpp
+++ b/libcxx/src/iostream.cpp
@@ -6,11 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__locale>
-#include <__std_stream>
 #include <new>
 #include <string>
 
+#include "include/std_stream.h"
+
 #define _str(s) #s
 #define str(s) _str(s)
 #define _LIBCPP_ABI_NAMESPACE_STR str(_LIBCPP_ABI_NAMESPACE)
diff --git a/libcxx/src/legacy_pointer_safety.cpp b/libcxx/src/legacy_pointer_safety.cpp
--- a/libcxx/src/legacy_pointer_safety.cpp
+++ b/libcxx/src/legacy_pointer_safety.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include <__config>
+#include <cstddef>
 #include <memory>
 
 // Support for garbage collection was removed in C++23 by https://wg21.link/P2186R2. Libc++ implements
diff --git a/libcxx/src/locale.cpp b/libcxx/src/locale.cpp
--- a/libcxx/src/locale.cpp
+++ b/libcxx/src/locale.cpp
@@ -12,7 +12,7 @@
 #define _LCONV_C99
 #endif
 
-#include <__utility/unreachable.h>
+#include <utility>
 #include <algorithm>
 #include <clocale>
 #include <codecvt>
diff --git a/libcxx/src/memory.cpp b/libcxx/src/memory.cpp
--- a/libcxx/src/memory.cpp
+++ b/libcxx/src/memory.cpp
@@ -12,6 +12,7 @@
 #endif
 
 #include <memory>
+#include <typeinfo>
 
 #ifndef _LIBCPP_HAS_NO_THREADS
 #  include <mutex>
diff --git a/libcxx/src/new.cpp b/libcxx/src/new.cpp
--- a/libcxx/src/new.cpp
+++ b/libcxx/src/new.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__memory/aligned_alloc.h>
+#include <memory>
 #include <new>
 #include <stdlib.h>
 
diff --git a/libcxx/src/optional.cpp b/libcxx/src/optional.cpp
--- a/libcxx/src/optional.cpp
+++ b/libcxx/src/optional.cpp
@@ -6,7 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__availability>
 #include <optional>
 
 namespace std
diff --git a/libcxx/src/strstream.cpp b/libcxx/src/strstream.cpp
--- a/libcxx/src/strstream.cpp
+++ b/libcxx/src/strstream.cpp
@@ -7,12 +7,12 @@
 //===----------------------------------------------------------------------===//
 
 #include <__assert>
-#include <__utility/unreachable.h>
 #include <algorithm>
 #include <climits>
 #include <cstdlib>
 #include <cstring>
 #include <strstream>
+#include <utility>
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
diff --git a/libcxx/test/libcxx/private_headers.verify.cpp b/libcxx/test/libcxx/private_headers.verify.cpp
--- a/libcxx/test/libcxx/private_headers.verify.cpp
+++ b/libcxx/test/libcxx/private_headers.verify.cpp
@@ -586,7 +586,6 @@
 #include <__ranges/views.h> // expected-error@*:* {{use of private header from outside its module: '__ranges/views.h'}}
 #include <__ranges/zip_view.h> // expected-error@*:* {{use of private header from outside its module: '__ranges/zip_view.h'}}
 #include <__split_buffer> // expected-error@*:* {{use of private header from outside its module: '__split_buffer'}}
-#include <__std_stream> // expected-error@*:* {{use of private header from outside its module: '__std_stream'}}
 #include <__string/char_traits.h> // expected-error@*:* {{use of private header from outside its module: '__string/char_traits.h'}}
 #include <__string/constexpr_c_functions.h> // expected-error@*:* {{use of private header from outside its module: '__string/constexpr_c_functions.h'}}
 #include <__string/extern_template_lists.h> // expected-error@*:* {{use of private header from outside its module: '__string/extern_template_lists.h'}}
diff --git a/libcxx/test/libcxx/transitive_includes/cxx2b.csv b/libcxx/test/libcxx/transitive_includes/cxx2b.csv
--- a/libcxx/test/libcxx/transitive_includes/cxx2b.csv
+++ b/libcxx/test/libcxx/transitive_includes/cxx2b.csv
@@ -162,10 +162,19 @@
 expected initializer_list
 expected new
 expected version
+experimental/algorithm algorithm
+experimental/algorithm cstddef
+experimental/algorithm type_traits
 experimental/deque deque
 experimental/deque experimental/memory_resource
 experimental/forward_list experimental/memory_resource
 experimental/forward_list forward_list
+experimental/functional array
+experimental/functional cstddef
+experimental/functional functional
+experimental/functional type_traits
+experimental/functional unordered_map
+experimental/functional vector
 experimental/iterator cstddef
 experimental/iterator iosfwd
 experimental/iterator iterator
diff --git a/libcxx/utils/data/ignore_format.txt b/libcxx/utils/data/ignore_format.txt
--- a/libcxx/utils/data/ignore_format.txt
+++ b/libcxx/utils/data/ignore_format.txt
@@ -603,7 +603,6 @@
 libcxx/include/stdint.h
 libcxx/include/stdio.h
 libcxx/include/stdlib.h
-libcxx/include/__std_stream
 libcxx/include/streambuf
 libcxx/include/string
 libcxx/include/__string/char_traits.h
diff --git a/libcxx/utils/generate_iwyu_mapping.py b/libcxx/utils/generate_iwyu_mapping.py
--- a/libcxx/utils/generate_iwyu_mapping.py
+++ b/libcxx/utils/generate_iwyu_mapping.py
@@ -53,7 +53,6 @@
         elif i == '__mutex_base': continue
         elif i == '__node_handle': public = ['map', 'set', 'unordered_map', 'unordered_set']
         elif i == '__split_buffer': public = ['deque', 'vector']
-        elif i == '__std_stream': public = ['iostream']
         elif i == '__threading_support': public = ['atomic', 'mutex', 'semaphore', 'thread']
         elif i == '__tree': public = ['map', 'set']
         elif i == '__undef_macros': continue
diff --git a/libcxxabi/src/cxa_default_handlers.cpp b/libcxxabi/src/cxa_default_handlers.cpp
--- a/libcxxabi/src/cxa_default_handlers.cpp
+++ b/libcxxabi/src/cxa_default_handlers.cpp
@@ -11,6 +11,7 @@
 
 #include <exception>
 #include <memory>
+#include <new>
 #include <stdlib.h>
 #include "abort_message.h"
 #include "cxxabi.h"
diff --git a/libcxxabi/src/fallback_malloc.cpp b/libcxxabi/src/fallback_malloc.cpp
--- a/libcxxabi/src/fallback_malloc.cpp
+++ b/libcxxabi/src/fallback_malloc.cpp
@@ -15,8 +15,9 @@
 #endif
 #endif
 
-#include <__memory/aligned_alloc.h>
 #include <assert.h>
+#include <atomic>
+#include <memory>
 #include <stdlib.h> // for malloc, calloc, free
 #include <string.h> // for memset