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
@@ -17,6 +17,14 @@
 # goal being to reduce the load on testers when a commit is known to fail.
 #
 
+# The Linux CI runners use the nightly ToT build provided by the Docker image.
+# (Note the image isn't updated daily.) The LLVM_HEAD_VERSION contains that
+# version number. The Linux CI runners for GCC use the latest stable version.
+# Theses numbers are available in all runners, making it easier to update the
+# version number.
+env:
+    LLVM_HEAD_VERSION: "16"
+    GCC_STABLE_VERSION: "12"
 steps:
   #
   # Light pre-commit tests for things like formatting or when people forget
@@ -76,6 +84,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -90,6 +101,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -104,6 +118,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -118,6 +135,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-15" #${LLVM_HEAD_VERSION}"
+        CXX: "clang++-15" #${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -132,6 +152,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "gcc-${GCC_STABLE_VERSION}"
+        CXX: "g++-${GCC_STABLE_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -194,6 +217,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "gcc-${GCC_STABLE_VERSION}"
+        CXX: "g++-${GCC_STABLE_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -204,10 +230,13 @@
     timeout_in_minutes: 120
 
   - label: "Clang 13"
-    command: "libcxx/utils/ci/run-buildbot generic-clang-13"
+    command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-13"
+        CXX: "clang++-13"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -218,7 +247,27 @@
     timeout_in_minutes: 120
 
   - label: "Clang 14"
-    command: "libcxx/utils/ci/run-buildbot generic-clang-14"
+    command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
+    env:
+        CC: "clang-14"
+        CXX: "clang++-14"
+    artifact_paths:
+      - "**/test-results.xml"
+      - "**/*.abilist"
+    agents:
+      queue: "libcxx-builders"
+      os: "linux"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
+    timeout_in_minutes: 120
+
+  - label: "Clang 15"
+    command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
+    env:
+        CC: "clang-15"
+        CXX: "clang++-15"
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
@@ -239,6 +288,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -253,6 +305,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -267,6 +322,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -281,6 +339,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -312,6 +373,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -326,6 +390,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -341,6 +408,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -355,6 +425,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -369,6 +442,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -383,6 +459,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -397,6 +476,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -411,6 +493,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -427,6 +512,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -441,6 +529,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -455,6 +546,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -469,6 +563,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -483,6 +580,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -497,6 +597,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -511,6 +614,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -525,6 +631,9 @@
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
+      env:
+          CC: "clang-${LLVM_HEAD_VERSION}"
+          CXX: "clang++-${LLVM_HEAD_VERSION}"
       agents:
         queue: "libcxx-builders"
         os: "linux"
@@ -539,6 +648,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -554,6 +666,9 @@
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+    env:
+        CC: "clang-${LLVM_HEAD_VERSION}"
+        CXX: "clang++-${LLVM_HEAD_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"
@@ -845,6 +960,8 @@
         - "**/test-results.xml"
         - "**/*.abilist"
       env:
+          CC: "clang"
+          CXX: "clang++"
           OBJECT_MODE: "32"
       agents:
           queue: libcxx-builders
@@ -861,6 +978,8 @@
         - "**/test-results.xml"
         - "**/*.abilist"
       env:
+          CC: "clang"
+          CXX: "clang++"
           OBJECT_MODE: "64"
       agents:
           queue: libcxx-builders
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
@@ -263,25 +263,7 @@
                    -DLIBUNWIND_TEST_CONFIG="llvm-libunwind-merged.cfg.in"
     check-runtimes
 ;;
-generic-clang-13)
-    export CC=clang-13
-    export CXX=clang++-13
-    clean
-    generate-cmake
-    check-runtimes
-    check-abi-list
-;;
-generic-clang-14)
-    export CC=clang-14
-    export CXX=clang++-14
-    clean
-    generate-cmake
-    check-runtimes
-    check-abi-list
-;;
 generic-gcc)
-    export CC=gcc-12
-    export CXX=g++-12
     clean
     generate-cmake -DLIBCXX_ENABLE_WERROR=NO \
                    -DLIBCXXABI_ENABLE_WERROR=NO \
@@ -289,8 +271,6 @@
     check-runtimes
 ;;
 generic-gcc-cxx11)
-    export CC=gcc-12
-    export CXX=g++-12
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx11.cmake" \
                    -DLIBCXX_ENABLE_WERROR=NO \
@@ -623,8 +603,6 @@
     ${NINJA} -vC "${BUILD_DIR}" check-cxx
 ;;
 aix)
-    export CC=clang
-    export CXX=clang++
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/AIX.cmake" \
                    -DLIBCXX_TEST_CONFIG="ibm-libc++-shared.cfg.in" \