diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -189,12 +189,6 @@
 
 option(CLANG_DEFAULT_PIE_ON_LINUX "Default to -fPIE and -pie on linux-gnu" ON)
 
-# TODO: verify the values against LangStandards.def?
-set(CLANG_DEFAULT_STD_C "" CACHE STRING
-  "Default standard to use for C/ObjC code (IDENT from LangStandards.def, empty for platform default)")
-set(CLANG_DEFAULT_STD_CXX "" CACHE STRING
-  "Default standard to use for C++/ObjC++ code (IDENT from LangStandards.def, empty for platform default)")
-
 set(CLANG_DEFAULT_LINKER "" CACHE STRING
   "Default linker to use (linker name or absolute path, empty for platform default)")
 
diff --git a/clang/include/clang/Config/config.h.cmake b/clang/include/clang/Config/config.h.cmake
--- a/clang/include/clang/Config/config.h.cmake
+++ b/clang/include/clang/Config/config.h.cmake
@@ -14,24 +14,6 @@
 /* Default linker to use. */
 #define CLANG_DEFAULT_LINKER "${CLANG_DEFAULT_LINKER}"
 
-/* Default C/ObjC standard to use. */
-#cmakedefine CLANG_DEFAULT_STD_C LangStandard::lang_${CLANG_DEFAULT_STD_C}
-/* Always #define something so that missing the config.h #include at use sites
- * becomes a compile error.
- */
-#ifndef CLANG_DEFAULT_STD_C
-#define CLANG_DEFAULT_STD_C LangStandard::lang_unspecified
-#endif
-
-/* Default C++/ObjC++ standard to use. */
-#cmakedefine CLANG_DEFAULT_STD_CXX LangStandard::lang_${CLANG_DEFAULT_STD_CXX}
-/* Always #define something so that missing the config.h #include at use sites
- * becomes a compile error.
- */
-#ifndef CLANG_DEFAULT_STD_CXX
-#define CLANG_DEFAULT_STD_CXX LangStandard::lang_unspecified
-#endif
-
 /* Default C++ stdlib to use. */
 #define CLANG_DEFAULT_CXX_STDLIB "${CLANG_DEFAULT_CXX_STDLIB}"
 
diff --git a/clang/lib/Basic/LangStandards.cpp b/clang/lib/Basic/LangStandards.cpp
--- a/clang/lib/Basic/LangStandards.cpp
+++ b/clang/lib/Basic/LangStandards.cpp
@@ -58,23 +58,14 @@
     return LangStandard::lang_cuda;
   case Language::Asm:
   case Language::C:
-    if (CLANG_DEFAULT_STD_C != LangStandard::lang_unspecified)
-      return CLANG_DEFAULT_STD_C;
-
     // The PS4 uses C99 as the default C standard.
     if (T.isPS4())
       return LangStandard::lang_gnu99;
     return LangStandard::lang_gnu17;
   case Language::ObjC:
-    if (CLANG_DEFAULT_STD_C != LangStandard::lang_unspecified)
-      return CLANG_DEFAULT_STD_C;
-
     return LangStandard::lang_gnu11;
   case Language::CXX:
   case Language::ObjCXX:
-    if (CLANG_DEFAULT_STD_CXX != LangStandard::lang_unspecified)
-      return CLANG_DEFAULT_STD_CXX;
-
     if (T.isPS())
       return LangStandard::lang_gnucxx14;
     return LangStandard::lang_gnucxx17;
diff --git a/clang/test/Preprocessor/lang-std.cpp b/clang/test/Preprocessor/lang-std.cpp
--- a/clang/test/Preprocessor/lang-std.cpp
+++ b/clang/test/Preprocessor/lang-std.cpp
@@ -1,5 +1,5 @@
-// UNSUPPORTED: default-std-cxx, ps4, ps5
-/// Test default standards when CLANG_DEFAULT_STD_CXX is unspecified.
+// UNSUPPORTED: ps4, ps5
+/// Test default standards.
 /// PS4/PS5 default to gnu++14.
 
 // RUN: %clang_cc1 -dM -E %s | FileCheck --check-prefix=CXX17 %s
diff --git a/clang/test/lit.cfg.py b/clang/test/lit.cfg.py
--- a/clang/test/lit.cfg.py
+++ b/clang/test/lit.cfg.py
@@ -126,9 +126,6 @@
 if config.clang_default_pie_on_linux:
     config.available_features.add('default-pie-on-linux')
 
-if config.clang_default_std_cxx != '':
-    config.available_features.add('default-std-cxx')
-
 # Set available features we allow tests to conditionalize on.
 #
 if config.clang_default_cxx_stdlib != '':
diff --git a/clang/test/lit.site.cfg.py.in b/clang/test/lit.site.cfg.py.in
--- a/clang/test/lit.site.cfg.py.in
+++ b/clang/test/lit.site.cfg.py.in
@@ -24,7 +24,6 @@
 config.have_zstd = @LLVM_ENABLE_ZSTD@
 config.clang_arcmt = @CLANG_ENABLE_ARCMT@
 config.clang_default_pie_on_linux = @CLANG_DEFAULT_PIE_ON_LINUX@
-config.clang_default_std_cxx = "@CLANG_DEFAULT_STD_CXX@"
 config.clang_default_cxx_stdlib = "@CLANG_DEFAULT_CXX_STDLIB@"
 config.clang_staticanalyzer = @CLANG_ENABLE_STATIC_ANALYZER@
 config.clang_staticanalyzer_z3 = @LLVM_WITH_Z3@
diff --git a/llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn b/llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn
--- a/llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn
+++ b/llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn
@@ -11,8 +11,6 @@
     "BUG_REPORT_URL=https://github.com/llvm/llvm-project/issues/",
     "CLANG_DEFAULT_PIE_ON_LINUX=1",
     "CLANG_DEFAULT_LINKER=",
-    "CLANG_DEFAULT_STD_C=",
-    "CLANG_DEFAULT_STD_CXX=",
     "CLANG_DEFAULT_CXX_STDLIB=",
     "CLANG_DEFAULT_RTLIB=",
     "CLANG_DEFAULT_OBJCOPY=objcopy",
diff --git a/llvm/utils/gn/secondary/clang/test/BUILD.gn b/llvm/utils/gn/secondary/clang/test/BUILD.gn
--- a/llvm/utils/gn/secondary/clang/test/BUILD.gn
+++ b/llvm/utils/gn/secondary/clang/test/BUILD.gn
@@ -46,7 +46,6 @@
     "LLVM_WITH_Z3=0",
     "CLANG_BUILD_EXAMPLES=0",
     "CLANG_BUILT_STANDALONE=0",
-    "CLANG_DEFAULT_STD_CXX=",
     "CLANG_DEFAULT_CXX_STDLIB=",  # Empty string means "default value" here.
     "CLANG_DEFAULT_PIE_ON_LINUX=0",
     "CLANG_PLUGIN_SUPPORT=0",  # FIXME: Analysis/plugins need global -fPIC
diff --git a/utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h b/utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h
--- a/utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h
+++ b/utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h
@@ -28,24 +28,6 @@
 /* Default linker to use. */
 #define CLANG_DEFAULT_LINKER ""
 
-/* Default C/ObjC standard to use. */
-/* #undef CLANG_DEFAULT_STD_C */
-/* Always #define something so that missing the config.h #include at use sites
- * becomes a compile error.
- */
-#ifndef CLANG_DEFAULT_STD_C
-#define CLANG_DEFAULT_STD_C LangStandard::lang_unspecified
-#endif
-
-/* Default C++/ObjC++ standard to use. */
-/* #undef CLANG_DEFAULT_STD_CXX */
-/* Always #define something so that missing the config.h #include at use sites
- * becomes a compile error.
- */
-#ifndef CLANG_DEFAULT_STD_CXX
-#define CLANG_DEFAULT_STD_CXX LangStandard::lang_unspecified
-#endif
-
 /* Default C++ stdlib to use. */
 #define CLANG_DEFAULT_CXX_STDLIB ""