diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index 83d9be8ccd402..4ce8f48292eec 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -1295,6 +1295,26 @@ void DarwinClang::addClangTargetOptions(
   Action::OffloadKind DeviceOffloadKind) const {
 
   Darwin::addClangTargetOptions(DriverArgs, CC1Args, DeviceOffloadKind);
+
+  /* TO_UPSTREAM(BoundsSafety) ON*/
+  // When `-fbounds-safety` and new userspace Libc attributes are enabled
+  // set a macro that userspace Libc will look for to decide whether or not to
+  // enable -fbounds-safety annotations in its headers (rdar://84733153). This
+  // is only being set during the gradual enablement of new checks and will be
+  // removed once the transition is complete (rdar://137912561).
+  if (DriverArgs.hasFlagNoClaim(options::OPT_fbounds_safety,
+                                options::OPT_fno_bounds_safety, false)) {
+    LangOptions::BoundsSafetyNewChecksMaskIntTy NewChecks =
+        ParseBoundsSafetyNewChecksMaskFromArgs(DriverArgs,
+                                               /*DiagnosticsEngine=*/nullptr);
+    if (NewChecks & LangOptions::BS_CHK_LibCAttributes) {
+      bool TargetWithoutUserspaceLibc = false;
+      if (getTriple().isOSDarwin() && !TargetWithoutUserspaceLibc) {
+        CC1Args.push_back("-D__LIBC_STAGED_BOUNDS_SAFETY_ATTRIBUTES");
+      }
+    }
+  }
+  /* TO_UPSTREAM(BoundsSafety) OFF*/
 }
 
 /// Take a path that speculatively points into Xcode and return the
diff --git a/clang/test/BoundsSafety/Driver/libc_staged_bounds_safety_attributes_macro.c b/clang/test/BoundsSafety/Driver/libc_staged_bounds_safety_attributes_macro.c
new file mode 100644
index 0000000000000..fce161eb6c876
--- /dev/null
+++ b/clang/test/BoundsSafety/Driver/libc_staged_bounds_safety_attributes_macro.c
@@ -0,0 +1,93 @@
+// =============================================================================
+// Supported target triples
+// =============================================================================
+
+// MACRO: -D__LIBC_STAGED_BOUNDS_SAFETY_ATTRIBUTES
+// NO_MACRO-NOT: -D__LIBC_STAGED_BOUNDS_SAFETY_ATTRIBUTES
+
+// ios
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=MACRO %s
+
+// macos
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-macos \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-macos \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=MACRO %s
+
+// macos (legacy `darwin` os name in triple)
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-darwin \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-darwin \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=MACRO %s
+
+// watchos
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-watchos \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-watchos \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=MACRO %s
+
+// tvos
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-tvos \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-tvos \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=MACRO %s
+
+// =============================================================================
+// Check option is included in all and option variant without `=all` suffix
+// =============================================================================
+
+// ios
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=all \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fno-bounds-safety-bringup-missing-checks \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
+
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fbounds-safety-bringup-missing-checks=all \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=MACRO %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fbounds-safety-bringup-missing-checks \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=MACRO %s
+
+// =============================================================================
+// Unsupported target triples
+// =============================================================================
+
+// linux
+// RUN: %clang -Wno-incompatible-sysroot -target x86_64-unknown-linux \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
+// RUN: %clang -Wno-incompatible-sysroot -target x86_64-unknown-linux \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -### -fbounds-safety %s 2>&1 \
+// RUN: | FileCheck --check-prefix=NO_MACRO %s
diff --git a/clang/test/BoundsSafety/Frontend/libc_staged_bounds_safety_attributes_macro.c b/clang/test/BoundsSafety/Frontend/libc_staged_bounds_safety_attributes_macro.c
new file mode 100644
index 0000000000000..bbf95b99b414c
--- /dev/null
+++ b/clang/test/BoundsSafety/Frontend/libc_staged_bounds_safety_attributes_macro.c
@@ -0,0 +1,84 @@
+// This is similar to the driver test of the same name but we verify that
+// the macro is actually set/unset as expected.
+
+// =============================================================================
+// Supported target triples
+// =============================================================================
+
+// ios
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=macro -fbounds-safety -fsyntax-only %s
+
+// macos
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-macos \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-macos \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=macro -fbounds-safety -fsyntax-only %s
+
+// macos (legacy `darwin` os name in triple)
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-darwin \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-darwin \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=macro -fbounds-safety -fsyntax-only %s
+
+// watchos
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-watchos \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-watchos \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=macro -fbounds-safety -fsyntax-only %s
+
+// tvos
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-tvos \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-tvos \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=macro -fbounds-safety -fsyntax-only %s
+
+// =============================================================================
+// Unsupported target triples
+// =============================================================================
+
+// linux
+// RUN: %clang -Wno-incompatible-sysroot -target x86_64-unknown-linux \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+// RUN: %clang -Wno-incompatible-sysroot -target x86_64-unknown-linux \
+// RUN:  -fbounds-safety-bringup-missing-checks=libc_attributes \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+
+// =============================================================================
+// Check option is included in all and option variant without `=all` suffix
+// =============================================================================
+
+// ios
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fno-bounds-safety-bringup-missing-checks=all \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fno-bounds-safety-bringup-missing-checks \
+// RUN:  -x c -Xclang -verify=no_macro -fbounds-safety -fsyntax-only %s
+
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fbounds-safety-bringup-missing-checks=all \
+// RUN:  -x c -Xclang -verify=macro -fbounds-safety -fsyntax-only %s
+// RUN: %clang -Wno-incompatible-sysroot -target arm64-apple-ios \
+// RUN:  -fbounds-safety-bringup-missing-checks \
+// RUN:  -x c -Xclang -verify=macro -fbounds-safety -fsyntax-only %s
+
+#ifndef __LIBC_STAGED_BOUNDS_SAFETY_ATTRIBUTES
+// no_macro-error@+1{{expected __LIBC_STAGED_BOUNDS_SAFETY_ATTRIBUTES macro}}
+#error expected __LIBC_STAGED_BOUNDS_SAFETY_ATTRIBUTES macro
+#endif
+
+// macro-no-diagnostics