diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
--- a/libcxx/docs/ReleaseNotes.rst
+++ b/libcxx/docs/ReleaseNotes.rst
@@ -85,3 +85,7 @@
 
 Build System Changes
 --------------------
+
+- Building libc++ and libc++abi for Apple platforms now requires targetting macOS 10.13 and later.
+  This is relevant for vendors building the libc++ shared library and for folks statically linking
+  libc++ into an application that has back-deployment requirements on Apple platforms.
diff --git a/libcxx/docs/index.rst b/libcxx/docs/index.rst
--- a/libcxx/docs/index.rst
+++ b/libcxx/docs/index.rst
@@ -116,7 +116,7 @@
 =============== ========================= ============================
 Target platform Target architecture       Notes
 =============== ========================= ============================
-macOS 10.9+     i386, x86_64, arm64       Building the shared library itself requires targetting macOS 10.11+
+macOS 10.9+     i386, x86_64, arm64       Building the shared library itself requires targetting macOS 10.13+
 FreeBSD 10+     i386, x86_64, arm
 Linux           i386, x86_64, arm, arm64
 Windows         i386, x86_64              Both MSVC and MinGW style environments
diff --git a/libcxx/src/chrono.cpp b/libcxx/src/chrono.cpp
--- a/libcxx/src/chrono.cpp
+++ b/libcxx/src/chrono.cpp
@@ -167,59 +167,6 @@
 
 #if defined(__APPLE__)
 
-// TODO(ldionne):
-// This old implementation of steady_clock is retained until Chrome drops supports
-// for macOS < 10.12. The issue is that they link libc++ statically into their
-// application, which means that libc++ must support being built for such deployment
-// targets. See https://llvm.org/D74489 for details.
-#if (defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200) || \
-    (defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__) && __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ < 100000) || \
-    (defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__) && __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ < 100000) || \
-    (defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__) && __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ < 30000)
-# define _LIBCPP_USE_OLD_MACH_ABSOLUTE_TIME
-#endif
-
-#if defined(_LIBCPP_USE_OLD_MACH_ABSOLUTE_TIME)
-
-//   mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
-//   nanoseconds since the computer booted up.  MachInfo.numer and MachInfo.denom
-//   are run time constants supplied by the OS.  This clock has no relationship
-//   to the Gregorian calendar.  It's main use is as a high resolution timer.
-
-// MachInfo.numer / MachInfo.denom is often 1 on the latest equipment.  Specialize
-//   for that case as an optimization.
-
-static steady_clock::rep steady_simplified() {
-    return static_cast<steady_clock::rep>(mach_absolute_time());
-}
-static double compute_steady_factor() {
-    mach_timebase_info_data_t MachInfo;
-    mach_timebase_info(&MachInfo);
-    return static_cast<double>(MachInfo.numer) / MachInfo.denom;
-}
-
-static steady_clock::rep steady_full() {
-    static const double factor = compute_steady_factor();
-    return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
-}
-
-typedef steady_clock::rep (*FP)();
-
-static FP init_steady_clock() {
-    mach_timebase_info_data_t MachInfo;
-    mach_timebase_info(&MachInfo);
-    if (MachInfo.numer == MachInfo.denom)
-        return &steady_simplified;
-    return &steady_full;
-}
-
-static steady_clock::time_point __libcpp_steady_clock_now() {
-    static FP fp = init_steady_clock();
-    return steady_clock::time_point(steady_clock::duration(fp()));
-}
-
-#else // vvvvv default behavior for Apple platforms  vvvvv
-
 // On Apple platforms, only CLOCK_UPTIME_RAW, CLOCK_MONOTONIC_RAW or
 // mach_absolute_time are able to time functions in the nanosecond range.
 // Furthermore, only CLOCK_MONOTONIC_RAW is truly monotonic, because it
@@ -232,8 +179,6 @@
     return steady_clock::time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
 }
 
-#endif
-
 #elif defined(_LIBCPP_WIN32API)
 
 // https://msdn.microsoft.com/en-us/library/windows/desktop/ms644905(v=vs.85).aspx says:
diff --git a/libcxx/src/filesystem/filesystem_common.h b/libcxx/src/filesystem/filesystem_common.h
--- a/libcxx/src/filesystem/filesystem_common.h
+++ b/libcxx/src/filesystem/filesystem_common.h
@@ -34,14 +34,9 @@
 # include <unistd.h>
 #endif // defined(_LIBCPP_WIN32API)
 
-#include "../include/apple_availability.h"
-
-#if !defined(__APPLE__)
-// We can use the presence of UTIME_OMIT to detect platforms that provide
-// utimensat.
+// We can use the presence of UTIME_OMIT to detect platforms that provide utimensat.
 #if defined(UTIME_OMIT)
-#define _LIBCPP_USE_UTIMENSAT
-#endif
+# define _LIBCPP_USE_UTIMENSAT
 #endif
 
 _LIBCPP_DIAGNOSTIC_PUSH
diff --git a/libcxx/src/include/apple_availability.h b/libcxx/src/include/apple_availability.h
--- a/libcxx/src/include/apple_availability.h
+++ b/libcxx/src/include/apple_availability.h
@@ -11,24 +11,6 @@
 
 #if defined(__APPLE__)
 
-#if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__)
-#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101300
-#define _LIBCPP_USE_UTIMENSAT
-#endif
-#elif defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__)
-#if __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ >= 110000
-#define _LIBCPP_USE_UTIMENSAT
-#endif
-#elif defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__)
-#if __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ >= 110000
-#define _LIBCPP_USE_UTIMENSAT
-#endif
-#elif defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__)
-#if __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ >= 40000
-#define _LIBCPP_USE_UTIMENSAT
-#endif
-#endif // __ENVIRONMENT_.*_VERSION_MIN_REQUIRED__
-
 #if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__)
 #if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101500
 #define _LIBCPP_USE_ULOCK