diff --git a/libunwind/test/lit.cfg b/libunwind/test/lit.cfg
--- a/libunwind/test/lit.cfg
+++ b/libunwind/test/lit.cfg
@@ -67,4 +67,9 @@
 configuration = config_module.Configuration(lit_config, config)
 configuration.configure()
 configuration.print_config_info()
-config.test_format = configuration.get_test_format()
+if lit_config.params.get('use_new_format', False):
+    lit_config.note("Using the experimental libc++ testing format")
+    import libcxx.test.newformat
+    config.test_format = libcxx.test.newformat.CxxStandardLibraryTest()
+else:
+    config.test_format = configuration.get_test_format()