diff --git a/libcxx/modules/std.compat/cassert.inc b/libcxx/modules/std.compat/cassert.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cassert.inc
@@ -0,0 +1,12 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  // This module exports nothing.
+} // export
diff --git a/libcxx/modules/std.compat/cctype.inc b/libcxx/modules/std.compat/cctype.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cctype.inc
@@ -0,0 +1,25 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::isalnum;
+  using ::isalpha;
+  using ::isblank;
+  using ::iscntrl;
+  using ::isdigit;
+  using ::isgraph;
+  using ::islower;
+  using ::isprint;
+  using ::ispunct;
+  using ::isspace;
+  using ::isupper;
+  using ::isxdigit;
+  using ::tolower;
+  using ::toupper;
+} // export
diff --git a/libcxx/modules/std.compat/cerrno.inc b/libcxx/modules/std.compat/cerrno.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cerrno.inc
@@ -0,0 +1,12 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  // This module exports nothing.
+} // export
diff --git a/libcxx/modules/std.compat/cfenv.inc b/libcxx/modules/std.compat/cfenv.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cfenv.inc
@@ -0,0 +1,29 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  // types
+  using ::fenv_t;
+  using ::fexcept_t;
+
+  // functions
+  using ::feclearexcept;
+  using ::fegetexceptflag;
+  using ::feraiseexcept;
+  using ::fesetexceptflag;
+  using ::fetestexcept;
+
+  using ::fegetround;
+  using ::fesetround;
+
+  using ::fegetenv;
+  using ::feholdexcept;
+  using ::fesetenv;
+  using ::feupdateenv;
+} // export
diff --git a/libcxx/modules/std.compat/cfloat.inc b/libcxx/modules/std.compat/cfloat.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cfloat.inc
@@ -0,0 +1,12 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  // This module exports nothing.
+} // export
diff --git a/libcxx/modules/std.compat/cinttypes.inc b/libcxx/modules/std.compat/cinttypes.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cinttypes.inc
@@ -0,0 +1,25 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::imaxdiv_t;
+
+  using ::imaxabs;
+  using ::imaxdiv;
+  using ::strtoimax;
+  using ::strtoumax;
+  using ::wcstoimax;
+  using ::wcstoumax;
+
+  // abs is conditionally here, but always present in cmath.cppm. To avoid
+  // conflicing declarations omit the using here.
+
+  // div is conditionally here, but always present in cstdlib.cppm. To avoid
+  // conflicing declarations omit the using here.
+} // export
diff --git a/libcxx/modules/std.compat/climits.inc b/libcxx/modules/std.compat/climits.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/climits.inc
@@ -0,0 +1,12 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  // This module exports nothing.
+} // export
diff --git a/libcxx/modules/std.compat/clocale.inc b/libcxx/modules/std.compat/clocale.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/clocale.inc
@@ -0,0 +1,17 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+#ifndef _LIBCPP_HAS_NO_LOCALIZATION
+  using ::lconv;
+
+  using ::localeconv;
+  using ::setlocale;
+#endif // _LIBCPP_HAS_NO_LOCALIZATION
+} // export
diff --git a/libcxx/modules/std.compat/cmath.inc b/libcxx/modules/std.compat/cmath.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cmath.inc
@@ -0,0 +1,266 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::acos;
+  using ::acosf;
+  using ::acosl;
+
+  using ::asin;
+  using ::asinf;
+  using ::asinl;
+
+  using ::atan;
+  using ::atanf;
+  using ::atanl;
+
+  using ::atan2;
+  using ::atan2f;
+  using ::atan2l;
+
+  using ::cos;
+  using ::cosf;
+  using ::cosl;
+
+  using ::sin;
+  using ::sinf;
+  using ::sinl;
+
+  using ::tan;
+  using ::tanf;
+  using ::tanl;
+
+  using ::acosh;
+  using ::acoshf;
+  using ::acoshl;
+
+  using ::asinh;
+  using ::asinhf;
+  using ::asinhl;
+
+  using ::atanh;
+  using ::atanhf;
+  using ::atanhl;
+
+  using ::cosh;
+  using ::coshf;
+  using ::coshl;
+
+  using ::sinh;
+  using ::sinhf;
+  using ::sinhl;
+
+  using ::tanh;
+  using ::tanhf;
+  using ::tanhl;
+
+  using ::exp;
+  using ::expf;
+  using ::expl;
+
+  using ::exp2;
+  using ::exp2f;
+  using ::exp2l;
+
+  using ::expm1;
+  using ::expm1f;
+  using ::expm1l;
+
+  using ::frexp;
+  using ::frexpf;
+  using ::frexpl;
+
+  using ::ilogb;
+  using ::ilogbf;
+  using ::ilogbl;
+
+  using ::ldexp;
+  using ::ldexpf;
+  using ::ldexpl;
+
+  using ::log;
+  using ::logf;
+  using ::logl;
+
+  using ::log10;
+  using ::log10f;
+  using ::log10l;
+
+  using ::log1p;
+  using ::log1pf;
+  using ::log1pl;
+
+  using ::log2;
+  using ::log2f;
+  using ::log2l;
+
+  using ::logb;
+  using ::logbf;
+  using ::logbl;
+
+  using ::modf;
+  using ::modff;
+  using ::modfl;
+
+  using ::scalbn;
+  using ::scalbnf;
+  using ::scalbnl;
+
+  using ::scalbln;
+  using ::scalblnf;
+  using ::scalblnl;
+
+  using ::cbrt;
+  using ::cbrtf;
+  using ::cbrtl;
+
+  // [c.math.abs], absolute values
+  using ::abs;
+
+  using ::fabs;
+  using ::fabsf;
+  using ::fabsl;
+
+  using ::hypot;
+  using ::hypotf;
+  using ::hypotl;
+
+  // [c.math.hypot3], three-dimensional hypotenuse
+  using ::hypot;
+
+  using ::pow;
+  using ::powf;
+  using ::powl;
+
+  using ::sqrt;
+  using ::sqrtf;
+  using ::sqrtl;
+
+  using ::erf;
+  using ::erff;
+  using ::erfl;
+
+  using ::erfc;
+  using ::erfcf;
+  using ::erfcl;
+
+  using ::lgamma;
+  using ::lgammaf;
+  using ::lgammal;
+
+  using ::tgamma;
+  using ::tgammaf;
+  using ::tgammal;
+
+  using ::ceil;
+  using ::ceilf;
+  using ::ceill;
+
+  using ::floor;
+  using ::floorf;
+  using ::floorl;
+
+  using ::nearbyint;
+  using ::nearbyintf;
+  using ::nearbyintl;
+
+  using ::rint;
+  using ::rintf;
+  using ::rintl;
+
+  using ::lrint;
+  using ::lrintf;
+  using ::lrintl;
+
+  using ::llrint;
+  using ::llrintf;
+  using ::llrintl;
+
+  using ::round;
+  using ::roundf;
+  using ::roundl;
+
+  using ::lround;
+  using ::lroundf;
+  using ::lroundl;
+
+  using ::llround;
+  using ::llroundf;
+  using ::llroundl;
+
+  using ::trunc;
+  using ::truncf;
+  using ::truncl;
+
+  using ::fmod;
+  using ::fmodf;
+  using ::fmodl;
+
+  using ::remainder;
+  using ::remainderf;
+  using ::remainderl;
+
+  using ::remquo;
+  using ::remquof;
+  using ::remquol;
+
+  using ::copysign;
+  using ::copysignf;
+  using ::copysignl;
+
+  using ::nan;
+  using ::nanf;
+  using ::nanl;
+
+  using ::nextafter;
+  using ::nextafterf;
+  using ::nextafterl;
+
+  using ::nexttoward;
+  using ::nexttowardf;
+  using ::nexttowardl;
+
+  using ::fdim;
+  using ::fdimf;
+  using ::fdiml;
+
+  using ::fmax;
+  using ::fmaxf;
+  using ::fmaxl;
+
+  using ::fmin;
+  using ::fminf;
+  using ::fminl;
+
+  using ::fma;
+  using ::fmaf;
+  using ::fmal;
+
+  // [c.math.lerp], linear interpolation
+  // [support.c.headers.other]/1
+  // ...  placed within the global namespace scope, except for the functions
+  // described in [sf.cmath], the std::lerp function overloads ([c.math.lerp])
+  // ...
+
+  // [c.math.fpclass], classification / comparison functions
+  using ::fpclassify;
+  using ::isfinite;
+  using ::isgreater;
+  using ::isgreaterequal;
+  using ::isinf;
+  using ::isless;
+  using ::islessequal;
+  using ::islessgreater;
+  using ::isnan;
+  using ::isnormal;
+  using ::isunordered;
+  using ::signbit;
+
+  // [sf.cmath], mathematical special functions
+} // export
diff --git a/libcxx/modules/std.compat/csetjmp.inc b/libcxx/modules/std.compat/csetjmp.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/csetjmp.inc
@@ -0,0 +1,13 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::jmp_buf;
+  using ::longjmp;
+} // export
diff --git a/libcxx/modules/std.compat/csignal.inc b/libcxx/modules/std.compat/csignal.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/csignal.inc
@@ -0,0 +1,17 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::sig_atomic_t;
+
+  // [support.signal], signal handlers
+  using ::signal;
+
+  using ::raise;
+} // export
diff --git a/libcxx/modules/std.compat/cstdarg.inc b/libcxx/modules/std.compat/cstdarg.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cstdarg.inc
@@ -0,0 +1,10 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export { using ::va_list; } // export
diff --git a/libcxx/modules/std.compat/cstddef.inc b/libcxx/modules/std.compat/cstddef.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cstddef.inc
@@ -0,0 +1,22 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using std::max_align_t;
+  using std::nullptr_t;
+  using std::ptrdiff_t;
+  using std::size_t;
+
+  // [support.c.headers]/1
+  // ...  placed within the global namespace scope, except for ... the
+  // declaration of std::byte ([cstddef.syn]), and the functions and
+  // function templates described in [support.types.byteops]. ...
+
+  // [support.types.byteops], byte type operations
+} // export
diff --git a/libcxx/modules/std.compat/cstdint.inc b/libcxx/modules/std.compat/cstdint.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cstdint.inc
@@ -0,0 +1,50 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  // signed
+  using ::int8_t _LIBCPP_USING_IF_EXISTS;
+  using ::int16_t _LIBCPP_USING_IF_EXISTS;
+  using ::int32_t _LIBCPP_USING_IF_EXISTS;
+  using ::int64_t _LIBCPP_USING_IF_EXISTS;
+
+  using ::int_fast16_t;
+  using ::int_fast32_t;
+  using ::int_fast64_t;
+  using ::int_fast8_t;
+
+  using ::int_least16_t;
+  using ::int_least32_t;
+  using ::int_least64_t;
+  using ::int_least8_t;
+
+  using ::intmax_t;
+
+  using ::intptr_t _LIBCPP_USING_IF_EXISTS;
+
+  // unsigned
+  using ::uint8_t _LIBCPP_USING_IF_EXISTS;
+  using ::uint16_t _LIBCPP_USING_IF_EXISTS;
+  using ::uint32_t _LIBCPP_USING_IF_EXISTS;
+  using ::uint64_t _LIBCPP_USING_IF_EXISTS;
+
+  using ::uint_fast16_t;
+  using ::uint_fast32_t;
+  using ::uint_fast64_t;
+  using ::uint_fast8_t;
+
+  using ::uint_least16_t;
+  using ::uint_least32_t;
+  using ::uint_least64_t;
+  using ::uint_least8_t;
+
+  using ::uintmax_t;
+
+  using ::uintptr_t _LIBCPP_USING_IF_EXISTS;
+} // export
diff --git a/libcxx/modules/std.compat/cstdio.inc b/libcxx/modules/std.compat/cstdio.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cstdio.inc
@@ -0,0 +1,61 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::FILE;
+  using ::fpos_t;
+  using ::size_t;
+
+  using ::clearerr;
+  using ::fclose;
+  using ::feof;
+  using ::ferror;
+  using ::fflush;
+  using ::fgetc;
+  using ::fgetpos;
+  using ::fgets;
+  using ::fopen;
+  using ::fprintf;
+  using ::fputc;
+  using ::fputs;
+  using ::fread;
+  using ::freopen;
+  using ::fscanf;
+  using ::fseek;
+  using ::fsetpos;
+  using ::ftell;
+  using ::fwrite;
+  using ::getc;
+  using ::getchar;
+  using ::perror;
+  using ::printf;
+  using ::putc;
+  using ::putchar;
+  using ::puts;
+  using ::remove;
+  using ::rename;
+  using ::rewind;
+  using ::scanf;
+  using ::setbuf;
+  using ::setvbuf;
+  using ::snprintf;
+  using ::sprintf;
+  using ::sscanf;
+  using ::tmpfile;
+  using ::tmpnam;
+  using ::ungetc;
+  using ::vfprintf;
+  using ::vfscanf;
+  using ::vprintf;
+  using ::vscanf;
+  using ::vsnprintf;
+  using ::vsprintf;
+  using ::vsscanf;
+
+} // export
diff --git a/libcxx/modules/std.compat/cstdlib.inc b/libcxx/modules/std.compat/cstdlib.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cstdlib.inc
@@ -0,0 +1,72 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::div_t;
+  using ::ldiv_t;
+  using ::lldiv_t;
+  using ::size_t;
+
+  // [support.start.term], start and termination
+  using ::_Exit;
+  using ::abort;
+  using ::at_quick_exit;
+  using ::atexit;
+  using ::exit;
+  using ::quick_exit;
+
+  using ::getenv;
+  using ::system;
+
+  // [c.malloc], C library memory allocation
+  using ::aligned_alloc;
+  using ::calloc;
+  using ::free;
+  using ::malloc;
+  using ::realloc;
+
+  using ::atof;
+  using ::atoi;
+  using ::atol;
+  using ::atoll;
+  using ::strtod;
+  using ::strtof;
+  using ::strtol;
+  using ::strtold;
+  using ::strtoll;
+  using ::strtoul;
+  using ::strtoull;
+
+  // [c.mb.wcs], multibyte / wide string and character conversion functions
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+  using ::mblen;
+  using ::mbstowcs;
+  using ::mbtowc;
+  using ::wcstombs;
+  using ::wctomb;
+#endif
+  // [alg.c.library], C standard library algorithms
+  using ::bsearch;
+  using ::qsort;
+
+  // [c.math.rand], low-quality random number generation
+  using ::rand;
+  using ::srand;
+
+  // [c.math.abs], absolute values
+  using ::abs;
+
+  using ::labs;
+  using ::llabs;
+
+  using ::div;
+  using ::ldiv;
+  using ::lldiv;
+
+} // export
diff --git a/libcxx/modules/std.compat/cstring.inc b/libcxx/modules/std.compat/cstring.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cstring.inc
@@ -0,0 +1,36 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::size_t;
+
+  using ::memchr;
+  using ::memcmp;
+  using ::memcpy;
+  using ::memmove;
+  using ::memset;
+  using ::strcat;
+  using ::strchr;
+  using ::strcmp;
+  using ::strcoll;
+  using ::strcpy;
+  using ::strcspn;
+  using ::strerror;
+  using ::strlen;
+  using ::strncat;
+  using ::strncmp;
+  using ::strncpy;
+  using ::strpbrk;
+  using ::strrchr;
+  using ::strspn;
+  using ::strstr;
+  using ::strtok;
+  using ::strxfrm;
+
+} // export
diff --git a/libcxx/modules/std.compat/ctime.inc b/libcxx/modules/std.compat/ctime.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/ctime.inc
@@ -0,0 +1,28 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  using ::clock_t;
+  using ::size_t;
+  using ::time_t;
+
+  using ::timespec;
+  using ::tm;
+
+  using ::asctime;
+  using ::clock;
+  using ::ctime;
+  using ::difftime;
+  using ::gmtime;
+  using ::localtime;
+  using ::mktime;
+  using ::strftime;
+  using ::time;
+  using ::timespec_get;
+} // export
diff --git a/libcxx/modules/std.compat/cuchar.inc b/libcxx/modules/std.compat/cuchar.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cuchar.inc
@@ -0,0 +1,26 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+  // Note the Standard does not mark these symbols optional, but libc++'s header
+  // does. So this seems strictly not to be conforming.
+
+  // mbstate_t is conditionally here, but always present in cwchar.cppm. To avoid
+  // conflicing declarations omit the using here.
+
+  // size_t is conditionally here, but always present in cstddef.cppm. To avoid
+  // conflicing declarations omit the using here.
+
+  using ::mbrtoc8 _LIBCPP_USING_IF_EXISTS;
+  using ::c8rtomb _LIBCPP_USING_IF_EXISTS;
+  using ::mbrtoc16 _LIBCPP_USING_IF_EXISTS;
+  using ::c16rtomb _LIBCPP_USING_IF_EXISTS;
+  using ::mbrtoc32 _LIBCPP_USING_IF_EXISTS;
+  using ::c32rtomb _LIBCPP_USING_IF_EXISTS;
+} // export
diff --git a/libcxx/modules/std.compat/cwchar.inc b/libcxx/modules/std.compat/cwchar.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cwchar.inc
@@ -0,0 +1,80 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+  using ::mbstate_t;
+  using ::size_t;
+  using ::wint_t;
+
+  using ::tm;
+
+  using ::btowc;
+  using ::fgetwc;
+  using ::fgetws;
+  using ::fputwc;
+  using ::fputws;
+  using ::fwide;
+  using ::fwprintf;
+  using ::fwscanf;
+  using ::getwc;
+  using ::getwchar;
+  using ::putwc;
+  using ::putwchar;
+  using ::swprintf;
+  using ::swscanf;
+  using ::ungetwc;
+  using ::vfwprintf;
+  using ::vfwscanf;
+  using ::vswprintf;
+  using ::vswscanf;
+  using ::vwprintf;
+  using ::vwscanf;
+  using ::wcscat;
+  using ::wcschr;
+  using ::wcscmp;
+  using ::wcscoll;
+  using ::wcscpy;
+  using ::wcscspn;
+  using ::wcsftime;
+  using ::wcslen;
+  using ::wcsncat;
+  using ::wcsncmp;
+  using ::wcsncpy;
+  using ::wcspbrk;
+  using ::wcsrchr;
+  using ::wcsspn;
+  using ::wcsstr;
+  using ::wcstod;
+  using ::wcstof;
+  using ::wcstok;
+  using ::wcstol;
+  using ::wcstold;
+  using ::wcstoll;
+  using ::wcstoul;
+  using ::wcstoull;
+  using ::wcsxfrm;
+  using ::wctob;
+  using ::wmemchr;
+  using ::wmemcmp;
+  using ::wmemcpy;
+  using ::wmemmove;
+  using ::wmemset;
+  using ::wprintf;
+  using ::wscanf;
+
+  // [c.mb.wcs], multibyte / wide string and character conversion functions
+  using ::mbrlen;
+  using ::mbrtowc;
+  using ::mbsinit;
+  using ::mbsrtowcs;
+  using ::wcrtomb;
+  using ::wcsrtombs;
+#endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
+} // export
diff --git a/libcxx/modules/std.compat/cwctype.inc b/libcxx/modules/std.compat/cwctype.inc
new file mode 100644
--- /dev/null
+++ b/libcxx/modules/std.compat/cwctype.inc
@@ -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
+//
+//===----------------------------------------------------------------------===//
+
+export {
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+  using ::wctrans_t;
+  using ::wctype_t;
+  using ::wint_t;
+
+  using ::iswalnum;
+  using ::iswalpha;
+  using ::iswblank;
+  using ::iswcntrl;
+  using ::iswctype;
+  using ::iswdigit;
+  using ::iswgraph;
+  using ::iswlower;
+  using ::iswprint;
+  using ::iswpunct;
+  using ::iswspace;
+  using ::iswupper;
+  using ::iswxdigit;
+  using ::towctrans;
+  using ::towlower;
+  using ::towupper;
+  using ::wctrans;
+  using ::wctype;
+#endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
+} // export