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/__std_stream b/libcxx/include/__std_stream
deleted file mode 100644
--- a/libcxx/include/__std_stream
+++ /dev/null
@@ -1,361 +0,0 @@
-// -*- 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___STD_STREAM
-#define _LIBCPP___STD_STREAM
-
-#include <__config>
-#include <__locale>
-#include <cstdio>
-#include <istream>
-#include <ostream>
-
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC system_header
-#endif
-
-_LIBCPP_PUSH_MACROS
-#include <__undef_macros>
-
-
-_LIBCPP_BEGIN_NAMESPACE_STD
-
-static const int __limit = 8;
-
-// __stdinbuf
-
-template <class _CharT>
-class _LIBCPP_HIDDEN __stdinbuf
-    : public basic_streambuf<_CharT, char_traits<_CharT> >
-{
-public:
-    typedef _CharT                           char_type;
-    typedef char_traits<char_type>           traits_type;
-    typedef typename traits_type::int_type   int_type;
-    typedef typename traits_type::pos_type   pos_type;
-    typedef typename traits_type::off_type   off_type;
-    typedef typename traits_type::state_type state_type;
-
-    __stdinbuf(FILE* __fp, state_type* __st);
-
-protected:
-    virtual int_type underflow();
-    virtual int_type uflow();
-    virtual int_type pbackfail(int_type __c = traits_type::eof());
-    virtual void imbue(const locale& __loc);
-
-private:
-
-    FILE* __file_;
-    const codecvt<char_type, char, state_type>* __cv_;
-    state_type* __st_;
-    int __encoding_;
-    int_type __last_consumed_;
-    bool __last_consumed_is_next_;
-    bool __always_noconv_;
-
-    __stdinbuf(const __stdinbuf&);
-    __stdinbuf& operator=(const __stdinbuf&);
-
-    int_type __getchar(bool __consume);
-};
-
-template <class _CharT>
-__stdinbuf<_CharT>::__stdinbuf(FILE* __fp, state_type* __st)
-    : __file_(__fp),
-      __st_(__st),
-      __last_consumed_(traits_type::eof()),
-      __last_consumed_is_next_(false)
-{
-    imbue(this->getloc());
-}
-
-template <class _CharT>
-void
-__stdinbuf<_CharT>::imbue(const locale& __loc)
-{
-    __cv_ = &use_facet<codecvt<char_type, char, state_type> >(__loc);
-    __encoding_ = __cv_->encoding();
-    __always_noconv_ = __cv_->always_noconv();
-    if (__encoding_ > __limit)
-        __throw_runtime_error("unsupported locale for standard input");
-}
-
-template <class _CharT>
-typename __stdinbuf<_CharT>::int_type
-__stdinbuf<_CharT>::underflow()
-{
-    return __getchar(false);
-}
-
-template <class _CharT>
-typename __stdinbuf<_CharT>::int_type
-__stdinbuf<_CharT>::uflow()
-{
-    return __getchar(true);
-}
-
-template <class _CharT>
-typename __stdinbuf<_CharT>::int_type
-__stdinbuf<_CharT>::__getchar(bool __consume)
-{
-    if (__last_consumed_is_next_)
-    {
-        int_type __result = __last_consumed_;
-        if (__consume)
-        {
-            __last_consumed_ = traits_type::eof();
-            __last_consumed_is_next_ = false;
-        }
-        return __result;
-    }
-    char __extbuf[__limit];
-    int __nread = _VSTD::max(1, __encoding_);
-    for (int __i = 0; __i < __nread; ++__i)
-    {
-        int __c = getc(__file_);
-        if (__c == EOF)
-            return traits_type::eof();
-        __extbuf[__i] = static_cast<char>(__c);
-    }
-    char_type __1buf;
-    if (__always_noconv_)
-        __1buf = static_cast<char_type>(__extbuf[0]);
-    else
-    {
-        const char* __enxt;
-        char_type* __inxt;
-        codecvt_base::result __r;
-        do
-        {
-            state_type __sv_st = *__st_;
-            __r = __cv_->in(*__st_, __extbuf, __extbuf + __nread, __enxt,
-                                   &__1buf, &__1buf + 1, __inxt);
-            switch (__r)
-            {
-            case _VSTD::codecvt_base::ok:
-                break;
-            case codecvt_base::partial:
-                *__st_ = __sv_st;
-                if (__nread == sizeof(__extbuf))
-                    return traits_type::eof();
-                {
-                    int __c = getc(__file_);
-                    if (__c == EOF)
-                        return traits_type::eof();
-                    __extbuf[__nread] = static_cast<char>(__c);
-                }
-                ++__nread;
-                break;
-            case codecvt_base::error:
-                return traits_type::eof();
-            case _VSTD::codecvt_base::noconv:
-                __1buf = static_cast<char_type>(__extbuf[0]);
-                break;
-            }
-        } while (__r == _VSTD::codecvt_base::partial);
-    }
-    if (!__consume)
-    {
-        for (int __i = __nread; __i > 0;)
-        {
-            if (ungetc(traits_type::to_int_type(__extbuf[--__i]), __file_) == EOF)
-                return traits_type::eof();
-        }
-    }
-    else
-        __last_consumed_ = traits_type::to_int_type(__1buf);
-    return traits_type::to_int_type(__1buf);
-}
-
-template <class _CharT>
-typename __stdinbuf<_CharT>::int_type
-__stdinbuf<_CharT>::pbackfail(int_type __c)
-{
-    if (traits_type::eq_int_type(__c, traits_type::eof()))
-    {
-        if (!__last_consumed_is_next_)
-        {
-            __c = __last_consumed_;
-            __last_consumed_is_next_ = !traits_type::eq_int_type(__last_consumed_,
-                                                                 traits_type::eof());
-        }
-        return __c;
-    }
-    if (__last_consumed_is_next_)
-    {
-        char __extbuf[__limit];
-        char* __enxt;
-        const char_type __ci = traits_type::to_char_type(__last_consumed_);
-        const char_type* __inxt;
-        switch (__cv_->out(*__st_, &__ci, &__ci + 1, __inxt,
-                                  __extbuf, __extbuf + sizeof(__extbuf), __enxt))
-        {
-        case _VSTD::codecvt_base::ok:
-            break;
-        case _VSTD::codecvt_base::noconv:
-            __extbuf[0] = static_cast<char>(__last_consumed_);
-            __enxt = __extbuf + 1;
-            break;
-        case codecvt_base::partial:
-        case codecvt_base::error:
-            return traits_type::eof();
-        }
-        while (__enxt > __extbuf)
-            if (ungetc(*--__enxt, __file_) == EOF)
-                return traits_type::eof();
-    }
-    __last_consumed_ = __c;
-    __last_consumed_is_next_ = true;
-    return __c;
-}
-
-// __stdoutbuf
-
-template <class _CharT>
-class _LIBCPP_HIDDEN __stdoutbuf
-    : public basic_streambuf<_CharT, char_traits<_CharT> >
-{
-public:
-    typedef _CharT                           char_type;
-    typedef char_traits<char_type>           traits_type;
-    typedef typename traits_type::int_type   int_type;
-    typedef typename traits_type::pos_type   pos_type;
-    typedef typename traits_type::off_type   off_type;
-    typedef typename traits_type::state_type state_type;
-
-    __stdoutbuf(FILE* __fp, state_type* __st);
-
-protected:
-    virtual int_type overflow (int_type __c = traits_type::eof());
-    virtual streamsize xsputn(const char_type* __s, streamsize __n);
-    virtual int sync();
-    virtual void imbue(const locale& __loc);
-
-private:
-    FILE* __file_;
-    const codecvt<char_type, char, state_type>* __cv_;
-    state_type* __st_;
-    bool __always_noconv_;
-
-    __stdoutbuf(const __stdoutbuf&);
-    __stdoutbuf& operator=(const __stdoutbuf&);
-};
-
-template <class _CharT>
-__stdoutbuf<_CharT>::__stdoutbuf(FILE* __fp, state_type* __st)
-    : __file_(__fp),
-      __cv_(&use_facet<codecvt<char_type, char, state_type> >(this->getloc())),
-      __st_(__st),
-      __always_noconv_(__cv_->always_noconv())
-{
-}
-
-template <class _CharT>
-typename __stdoutbuf<_CharT>::int_type
-__stdoutbuf<_CharT>::overflow(int_type __c)
-{
-    char __extbuf[__limit];
-    char_type __1buf;
-    if (!traits_type::eq_int_type(__c, traits_type::eof()))
-    {
-        __1buf = traits_type::to_char_type(__c);
-        if (__always_noconv_)
-        {
-            if (fwrite(&__1buf, sizeof(char_type), 1, __file_) != 1)
-                return traits_type::eof();
-        }
-        else
-        {
-            char* __extbe = __extbuf;
-            codecvt_base::result __r;
-            char_type* pbase = &__1buf;
-            char_type* pptr = pbase + 1;
-            do
-            {
-                const char_type* __e;
-                __r = __cv_->out(*__st_, pbase, pptr, __e,
-                                        __extbuf,
-                                        __extbuf + sizeof(__extbuf),
-                                        __extbe);
-                if (__e == pbase)
-                    return traits_type::eof();
-                if (__r == codecvt_base::noconv)
-                {
-                    if (fwrite(pbase, 1, 1, __file_) != 1)
-                        return traits_type::eof();
-                }
-                else if (__r == codecvt_base::ok || __r == codecvt_base::partial)
-                {
-                    size_t __nmemb = static_cast<size_t>(__extbe - __extbuf);
-                    if (fwrite(__extbuf, 1, __nmemb, __file_) != __nmemb)
-                        return traits_type::eof();
-                    if (__r == codecvt_base::partial)
-                    {
-                        pbase = const_cast<char_type*>(__e);
-                    }
-                }
-                else
-                    return traits_type::eof();
-            } while (__r == codecvt_base::partial);
-        }
-    }
-    return traits_type::not_eof(__c);
-}
-
-template <class _CharT>
-streamsize
-__stdoutbuf<_CharT>::xsputn(const char_type* __s, streamsize __n)
-{
-    if (__always_noconv_)
-        return fwrite(__s, sizeof(char_type), __n, __file_);
-    streamsize __i = 0;
-    for (; __i < __n; ++__i, ++__s)
-        if (overflow(traits_type::to_int_type(*__s)) == traits_type::eof())
-            break;
-    return __i;
-}
-
-template <class _CharT>
-int
-__stdoutbuf<_CharT>::sync()
-{
-    char __extbuf[__limit];
-    codecvt_base::result __r;
-    do
-    {
-        char* __extbe;
-        __r = __cv_->unshift(*__st_, __extbuf,
-                                    __extbuf + sizeof(__extbuf),
-                                    __extbe);
-        size_t __nmemb = static_cast<size_t>(__extbe - __extbuf);
-        if (fwrite(__extbuf, 1, __nmemb, __file_) != __nmemb)
-            return -1;
-    } while (__r == codecvt_base::partial);
-    if (__r == codecvt_base::error)
-        return -1;
-    if (fflush(__file_))
-        return -1;
-    return 0;
-}
-
-template <class _CharT>
-void
-__stdoutbuf<_CharT>::imbue(const locale& __loc)
-{
-    sync();
-    __cv_ = &use_facet<codecvt<char_type, char, state_type> >(__loc);
-    __always_noconv_ = __cv_->always_noconv();
-}
-
-_LIBCPP_END_NAMESPACE_STD
-
-_LIBCPP_POP_MACROS
-
-#endif // _LIBCPP___STD_STREAM
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/src/include/std_stream.h b/libcxx/src/include/std_stream.h
new file mode 100644
--- /dev/null
+++ b/libcxx/src/include/std_stream.h
@@ -0,0 +1,299 @@
+// -*- 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___STD_STREAM
+#define _LIBCPP___STD_STREAM
+
+#include <__config>
+#include <cstdio>
+#include <istream>
+#include <locale>
+#include <ostream>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+static const int __limit = 8;
+
+// __stdinbuf
+
+template <class _CharT>
+class _LIBCPP_HIDDEN __stdinbuf : public basic_streambuf<_CharT, char_traits<_CharT> > {
+public:
+  typedef _CharT char_type;
+  typedef char_traits<char_type> traits_type;
+  typedef typename traits_type::int_type int_type;
+  typedef typename traits_type::pos_type pos_type;
+  typedef typename traits_type::off_type off_type;
+  typedef typename traits_type::state_type state_type;
+
+  __stdinbuf(FILE* __fp, state_type* __st);
+
+protected:
+  virtual int_type underflow();
+  virtual int_type uflow();
+  virtual int_type pbackfail(int_type __c = traits_type::eof());
+  virtual void imbue(const locale& __loc);
+
+private:
+  FILE* __file_;
+  const codecvt<char_type, char, state_type>* __cv_;
+  state_type* __st_;
+  int __encoding_;
+  int_type __last_consumed_;
+  bool __last_consumed_is_next_;
+  bool __always_noconv_;
+
+  __stdinbuf(const __stdinbuf&);
+  __stdinbuf& operator=(const __stdinbuf&);
+
+  int_type __getchar(bool __consume);
+};
+
+template <class _CharT>
+__stdinbuf<_CharT>::__stdinbuf(FILE* __fp, state_type* __st)
+    : __file_(__fp), __st_(__st), __last_consumed_(traits_type::eof()), __last_consumed_is_next_(false) {
+  imbue(this->getloc());
+}
+
+template <class _CharT>
+void __stdinbuf<_CharT>::imbue(const locale& __loc) {
+  __cv_            = &use_facet<codecvt<char_type, char, state_type> >(__loc);
+  __encoding_      = __cv_->encoding();
+  __always_noconv_ = __cv_->always_noconv();
+  if (__encoding_ > __limit)
+    __throw_runtime_error("unsupported locale for standard input");
+}
+
+template <class _CharT>
+typename __stdinbuf<_CharT>::int_type __stdinbuf<_CharT>::underflow() {
+  return __getchar(false);
+}
+
+template <class _CharT>
+typename __stdinbuf<_CharT>::int_type __stdinbuf<_CharT>::uflow() {
+  return __getchar(true);
+}
+
+template <class _CharT>
+typename __stdinbuf<_CharT>::int_type __stdinbuf<_CharT>::__getchar(bool __consume) {
+  if (__last_consumed_is_next_) {
+    int_type __result = __last_consumed_;
+    if (__consume) {
+      __last_consumed_         = traits_type::eof();
+      __last_consumed_is_next_ = false;
+    }
+    return __result;
+  }
+  char __extbuf[__limit];
+  int __nread = _VSTD::max(1, __encoding_);
+  for (int __i = 0; __i < __nread; ++__i) {
+    int __c = getc(__file_);
+    if (__c == EOF)
+      return traits_type::eof();
+    __extbuf[__i] = static_cast<char>(__c);
+  }
+  char_type __1buf;
+  if (__always_noconv_)
+    __1buf = static_cast<char_type>(__extbuf[0]);
+  else {
+    const char* __enxt;
+    char_type* __inxt;
+    codecvt_base::result __r;
+    do {
+      state_type __sv_st = *__st_;
+      __r                = __cv_->in(*__st_, __extbuf, __extbuf + __nread, __enxt, &__1buf, &__1buf + 1, __inxt);
+      switch (__r) {
+      case _VSTD::codecvt_base::ok:
+        break;
+      case codecvt_base::partial:
+        *__st_ = __sv_st;
+        if (__nread == sizeof(__extbuf))
+          return traits_type::eof();
+        {
+          int __c = getc(__file_);
+          if (__c == EOF)
+            return traits_type::eof();
+          __extbuf[__nread] = static_cast<char>(__c);
+        }
+        ++__nread;
+        break;
+      case codecvt_base::error:
+        return traits_type::eof();
+      case _VSTD::codecvt_base::noconv:
+        __1buf = static_cast<char_type>(__extbuf[0]);
+        break;
+      }
+    } while (__r == _VSTD::codecvt_base::partial);
+  }
+  if (!__consume) {
+    for (int __i = __nread; __i > 0;) {
+      if (ungetc(traits_type::to_int_type(__extbuf[--__i]), __file_) == EOF)
+        return traits_type::eof();
+    }
+  } else
+    __last_consumed_ = traits_type::to_int_type(__1buf);
+  return traits_type::to_int_type(__1buf);
+}
+
+template <class _CharT>
+typename __stdinbuf<_CharT>::int_type __stdinbuf<_CharT>::pbackfail(int_type __c) {
+  if (traits_type::eq_int_type(__c, traits_type::eof())) {
+    if (!__last_consumed_is_next_) {
+      __c                      = __last_consumed_;
+      __last_consumed_is_next_ = !traits_type::eq_int_type(__last_consumed_, traits_type::eof());
+    }
+    return __c;
+  }
+  if (__last_consumed_is_next_) {
+    char __extbuf[__limit];
+    char* __enxt;
+    const char_type __ci = traits_type::to_char_type(__last_consumed_);
+    const char_type* __inxt;
+    switch (__cv_->out(*__st_, &__ci, &__ci + 1, __inxt, __extbuf, __extbuf + sizeof(__extbuf), __enxt)) {
+    case _VSTD::codecvt_base::ok:
+      break;
+    case _VSTD::codecvt_base::noconv:
+      __extbuf[0] = static_cast<char>(__last_consumed_);
+      __enxt      = __extbuf + 1;
+      break;
+    case codecvt_base::partial:
+    case codecvt_base::error:
+      return traits_type::eof();
+    }
+    while (__enxt > __extbuf)
+      if (ungetc(*--__enxt, __file_) == EOF)
+        return traits_type::eof();
+  }
+  __last_consumed_         = __c;
+  __last_consumed_is_next_ = true;
+  return __c;
+}
+
+// __stdoutbuf
+
+template <class _CharT>
+class _LIBCPP_HIDDEN __stdoutbuf : public basic_streambuf<_CharT, char_traits<_CharT> > {
+public:
+  typedef _CharT char_type;
+  typedef char_traits<char_type> traits_type;
+  typedef typename traits_type::int_type int_type;
+  typedef typename traits_type::pos_type pos_type;
+  typedef typename traits_type::off_type off_type;
+  typedef typename traits_type::state_type state_type;
+
+  __stdoutbuf(FILE* __fp, state_type* __st);
+
+protected:
+  virtual int_type overflow(int_type __c = traits_type::eof());
+  virtual streamsize xsputn(const char_type* __s, streamsize __n);
+  virtual int sync();
+  virtual void imbue(const locale& __loc);
+
+private:
+  FILE* __file_;
+  const codecvt<char_type, char, state_type>* __cv_;
+  state_type* __st_;
+  bool __always_noconv_;
+
+  __stdoutbuf(const __stdoutbuf&);
+  __stdoutbuf& operator=(const __stdoutbuf&);
+};
+
+template <class _CharT>
+__stdoutbuf<_CharT>::__stdoutbuf(FILE* __fp, state_type* __st)
+    : __file_(__fp),
+      __cv_(&use_facet<codecvt<char_type, char, state_type> >(this->getloc())),
+      __st_(__st),
+      __always_noconv_(__cv_->always_noconv()) {}
+
+template <class _CharT>
+typename __stdoutbuf<_CharT>::int_type __stdoutbuf<_CharT>::overflow(int_type __c) {
+  char __extbuf[__limit];
+  char_type __1buf;
+  if (!traits_type::eq_int_type(__c, traits_type::eof())) {
+    __1buf = traits_type::to_char_type(__c);
+    if (__always_noconv_) {
+      if (fwrite(&__1buf, sizeof(char_type), 1, __file_) != 1)
+        return traits_type::eof();
+    } else {
+      char* __extbe = __extbuf;
+      codecvt_base::result __r;
+      char_type* pbase = &__1buf;
+      char_type* pptr  = pbase + 1;
+      do {
+        const char_type* __e;
+        __r = __cv_->out(*__st_, pbase, pptr, __e, __extbuf, __extbuf + sizeof(__extbuf), __extbe);
+        if (__e == pbase)
+          return traits_type::eof();
+        if (__r == codecvt_base::noconv) {
+          if (fwrite(pbase, 1, 1, __file_) != 1)
+            return traits_type::eof();
+        } else if (__r == codecvt_base::ok || __r == codecvt_base::partial) {
+          size_t __nmemb = static_cast<size_t>(__extbe - __extbuf);
+          if (fwrite(__extbuf, 1, __nmemb, __file_) != __nmemb)
+            return traits_type::eof();
+          if (__r == codecvt_base::partial) {
+            pbase = const_cast<char_type*>(__e);
+          }
+        } else
+          return traits_type::eof();
+      } while (__r == codecvt_base::partial);
+    }
+  }
+  return traits_type::not_eof(__c);
+}
+
+template <class _CharT>
+streamsize __stdoutbuf<_CharT>::xsputn(const char_type* __s, streamsize __n) {
+  if (__always_noconv_)
+    return fwrite(__s, sizeof(char_type), __n, __file_);
+  streamsize __i = 0;
+  for (; __i < __n; ++__i, ++__s)
+    if (overflow(traits_type::to_int_type(*__s)) == traits_type::eof())
+      break;
+  return __i;
+}
+
+template <class _CharT>
+int __stdoutbuf<_CharT>::sync() {
+  char __extbuf[__limit];
+  codecvt_base::result __r;
+  do {
+    char* __extbe;
+    __r            = __cv_->unshift(*__st_, __extbuf, __extbuf + sizeof(__extbuf), __extbe);
+    size_t __nmemb = static_cast<size_t>(__extbe - __extbuf);
+    if (fwrite(__extbuf, 1, __nmemb, __file_) != __nmemb)
+      return -1;
+  } while (__r == codecvt_base::partial);
+  if (__r == codecvt_base::error)
+    return -1;
+  if (fflush(__file_))
+    return -1;
+  return 0;
+}
+
+template <class _CharT>
+void __stdoutbuf<_CharT>::imbue(const locale& __loc) {
+  sync();
+  __cv_            = &use_facet<codecvt<char_type, char, state_type> >(__loc);
+  __always_noconv_ = __cv_->always_noconv();
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___STD_STREAM
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