diff --git a/libcxx/cmake/caches/Generic-abi-unstable.cmake b/libcxx/cmake/caches/Generic-abi-unstable.cmake
new file mode 100644
--- /dev/null
+++ b/libcxx/cmake/caches/Generic-abi-unstable.cmake
@@ -0,0 +1 @@
+set(LIBCXX_ABI_UNSTABLE ON CACHE BOOL "")
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
@@ -465,6 +465,19 @@
           limit: 2
     timeout_in_minutes: 120
 
+  - label: "Unstable ABI"
+    command: "libcxx/utils/ci/run-buildbot generic-abi-unstable"
+    artifact_paths:
+      - "**/test-results.xml"
+    agents:
+      queue: "libcxx-builders"
+      os: "linux"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
+    timeout_in_minutes: 120
+
   - label: "No experimental features"
     command: "libcxx/utils/ci/run-buildbot generic-no-experimental"
     artifact_paths:
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
@@ -395,6 +395,11 @@
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-no-experimental.cmake" \
                    -DLIBCXX_TEST_CONFIG="llvm-libc++-shared.cfg.in" \
                    -DLIBUNWIND_TEST_CONFIG="llvm-libunwind-shared.cfg.in"
+generic-abi-unstable)
+    clean
+    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-abi-unstable.cmake" \
+                   -DLIBCXX_TEST_CONFIG="llvm-libc++-shared.cfg.in" \
+                   -DLIBUNWIND_TEST_CONFIG="llvm-libunwind-shared.cfg.in"
     check-runtimes
 ;;
 apple-system)