diff --git a/libcxx/utils/ci/buildkite-pipeline.yml b/libcxx/utils/ci/buildkite-pipeline.yml
--- a/libcxx/utils/ci/buildkite-pipeline.yml
+++ b/libcxx/utils/ci/buildkite-pipeline.yml
@@ -634,7 +634,7 @@
   - group: ":apple: Apple"
     steps:
     - label: "MacOS x86_64"
-      command: "libcxx/utils/ci/run-buildbot generic-cxx20"
+      command: "libcxx/utils/ci/run-buildbot apple-cxx20"
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
@@ -649,7 +649,7 @@
       timeout_in_minutes: 120
 
     - label: "MacOS arm64"
-      command: "libcxx/utils/ci/run-buildbot generic-cxx20"
+      command: "libcxx/utils/ci/run-buildbot apple-cxx20"
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -12,6 +12,8 @@
 unset LANG
 unset LC_ALL
 unset LC_COLLATE
+export CC=clang-15
+export CXX=clang++-15
 
 PROGNAME="$(basename "${0}")"
 
@@ -214,6 +216,10 @@
     check-runtimes
     check-abi-list
 ;;
+apple-cxx20)
+    export -n CC
+    export -n CXX
+;& # Fallthrough
 generic-cxx20)
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx20.cmake"
@@ -370,6 +376,8 @@
     check-runtimes
 ;;
 apple-system)
+    export -n CC
+    export -n CXX
     clean
 
     arch="$(uname -m)"
@@ -386,6 +394,8 @@
     xcrun --sdk macosx ninja -vC "${BUILD_DIR}/${arch}" check-cxx check-cxxabi check-cxx-abilist
 ;;
 apple-system-backdeployment-*)
+    export -n CC
+    export -n CXX
     clean
 
     if [[ "${OSX_ROOTS}" == "" ]]; then
@@ -484,11 +494,15 @@
     check-runtimes
 ;;
 aarch64)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/AArch64.cmake"
     check-runtimes
 ;;
 aarch64-noexceptions)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/AArch64.cmake" \
                    -DLIBCXX_ENABLE_EXCEPTIONS=OFF \
@@ -497,22 +511,30 @@
 ;;
 # Aka Armv8 32 bit
 armv8)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Armv8Arm.cmake"
     check-runtimes
 ;;
 armv8-noexceptions)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Armv8Thumb-noexceptions.cmake"
     check-runtimes
 ;;
 # Armv7 32 bit. One building Arm only one Thumb only code.
 armv7)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Armv7Arm.cmake"
     check-runtimes
 ;;
 armv7-noexceptions)
+    export -n CC
+    export -n CXX
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Armv7Thumb-noexceptions.cmake"
     check-runtimes