diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
--- a/libcxx/utils/libcxx/test/params.py
+++ b/libcxx/utils/libcxx/test/params.py
@@ -135,7 +135,7 @@
             ])),
 
   # Parameters to enable or disable parts of the test suite
-  Parameter(name='enable_experimental', choices=[True, False], type=bool, default=False,
+  Parameter(name='enable_experimental', choices=[True, False], type=bool, default=True,
             help="Whether to enable tests for experimental C++ libraries (typically Library Fundamentals TSes).",
             actions=lambda experimental: [] if not experimental else [
               AddFeature('c++experimental'),
diff --git a/libcxxabi/test/lit.site.cfg.in b/libcxxabi/test/lit.site.cfg.in
--- a/libcxxabi/test/lit.site.cfg.in
+++ b/libcxxabi/test/lit.site.cfg.in
@@ -30,6 +30,7 @@
 config.sysroot                  = "@LIBCXXABI_SYSROOT@"
 config.gcc_toolchain            = "@LIBCXXABI_GCC_TOOLCHAIN@"
 config.cxx_ext_threads          = @LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY@
+config.enable_experimental      = False
 
 config.pstl_src_root            = "@ParallelSTL_SOURCE_DIR@" if @LIBCXX_ENABLE_PARALLEL_ALGORITHMS@ else None
 config.pstl_obj_root            = "@ParallelSTL_BINARY_DIR@" if @LIBCXX_ENABLE_PARALLEL_ALGORITHMS@ else None
diff --git a/libunwind/test/lit.site.cfg.in b/libunwind/test/lit.site.cfg.in
--- a/libunwind/test/lit.site.cfg.in
+++ b/libunwind/test/lit.site.cfg.in
@@ -29,6 +29,7 @@
 config.sysroot                  = "@LIBUNWIND_SYSROOT@"
 config.gcc_toolchain            = "@LIBUNWIND_GCC_TOOLCHAIN@"
 config.cxx_ext_threads          = @LIBUNWIND_BUILD_EXTERNAL_THREAD_LIBRARY@
+config.enable_experimental      = False
 
 site.addsitedir(os.path.join(config.libunwind_src_root, 'test'))
 site.addsitedir(os.path.join(config.libcxx_src_root, 'utils'))