diff --git a/.github/workflows/emscripten.yml b/.github/workflows/emscripten.yml
index 75fb1f310..74b57b952 100644
--- a/.github/workflows/emscripten.yml
+++ b/.github/workflows/emscripten.yml
@@ -77,6 +77,34 @@ jobs:
             llvm_enable_projects: "clang;lld"
             llvm_targets_to_build: "WebAssembly"
             emsdk_ver: "3.1.73"
+          - name: ubu24-arm-clang-repl-21-emscripten
+            os: ubuntu-24.04-arm
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: osx15-arm-clang-repl-21-emscripten
+            os: macos-15
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: ubu24-x86-clang-repl-21-emscripten
+            os: ubuntu-24.04
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: win2025-x86-clang-repl-21-emscripten
+            os: windows-2025
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
 
     steps:
     - uses: actions/checkout@v4
@@ -199,7 +227,7 @@ jobs:
         else
           # Apply patches
           llvm_vers=$(echo "${{ matrix.clang-runtime }}" | tr '[:lower:]' '[:upper:]')
-          if [[ "${llvm_vers}" == "19" || "${llvm_vers}" == "20" ]]; then
+          if [[ "${llvm_vers}" == "19" || "${llvm_vers}" == "20" || "${llvm_vers}" == "21"  ]]; then
             git apply -v ../patches/llvm/emscripten-clang${{ matrix.clang-runtime }}-*.patch
             echo "Apply emscripten-clang${{ matrix.clang-runtime }}-*.patch patches:"
           fi
@@ -314,6 +342,11 @@ jobs:
             git apply -v Windows-emscripten-clang20-1-CrossCompile.patch
             git apply -v emscripten-clang20-2-shift-temporary-files-to-tmp-dir.patch
           }
+          elseif ( "${{ matrix.clang-runtime }}" -imatch "21" )
+          {
+            git apply -v Windows-emscripten-clang21-1-CrossCompile.patch
+            git apply -v emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
+          }
           cd build
           echo "Apply clang${{ matrix.clang-runtime }}-*.patch patches:"
           emcmake cmake -DCMAKE_BUILD_TYPE=Release `
@@ -423,6 +456,30 @@ jobs:
             cling: Off
             micromamba_shell_init: powershell
             emsdk_ver: "3.1.73"
+          - name: ubu24-x86-clang-repl-21-emscripten_wasm
+            os: ubuntu-24.04
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: osx15-arm-clang-repl-21-emscripten_wasm
+            os: macos-15
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: ubu24-arm-clang-repl-21-emscripten_wasm
+            os: ubuntu-24.04-arm
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: win2025-x86-clang-repl-21-emscripten
+            os: windows-2025
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: powershell
+            emsdk_ver: "3.1.73"
 
     steps:
     - uses: actions/checkout@v4
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index bc40f0bea..605780436 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -23,6 +23,14 @@ jobs:
       matrix:
         include:
           # Ubuntu Arm Jobs
+          - name: ubu24-arm-gcc12-clang-repl-21
+            os: ubuntu-24.04-arm
+            compiler: gcc-12
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: ubu22-arm-gcc12-clang-repl-20-coverage
             os: ubuntu-22.04-arm
             compiler: gcc-12
@@ -66,6 +74,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Ubuntu X86 Jobs
+          - name: ubu24-x86-gcc12-clang-repl-21
+            os: ubuntu-24.04
+            compiler: gcc-12
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: ubu24-x86-gcc12-clang-repl-20
             os: ubuntu-24.04
             compiler: gcc-12
@@ -100,6 +116,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # MacOS Arm Jobs
+          - name: osx15-arm-clang-clang-repl-21
+            os: macos-15
+            compiler: clang
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host"
           - name: osx15-arm-clang-clang-repl-20
             os: macos-15
             compiler: clang
@@ -134,6 +158,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # MacOS X86 Jobs
+          - name: osx13-x86-clang-clang-repl-21
+            os: macos-13
+            compiler: clang
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host"
           - name: osx13-x86-clang-clang-repl-20
             os: macos-13
             compiler: clang
@@ -168,6 +200,13 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Windows Arm Jobs
+          - name: win11-msvc-clang-repl-21
+            os: windows-11-arm
+            compiler: msvc
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: win11-msvc-clang-repl-20
             os: windows-11-arm
             compiler: msvc
@@ -184,6 +223,13 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Windows X86 Jobs
+          - name: win2025-msvc-clang-repl-21
+            os: windows-2025
+            compiler: msvc
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: win2025-msvc-clang-repl-20
             os: windows-2025
             compiler: msvc
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 981c57ced..cc8d38617 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,14 +68,14 @@ include(GNUInstallDirs)
   ## Define supported version of clang and llvm
 
   set(CLANG_MIN_SUPPORTED 18.0)
-  set(CLANG_MAX_SUPPORTED "20.1.x")
-  set(CLANG_VERSION_UPPER_BOUND 21.0.0)
+  set(CLANG_MAX_SUPPORTED "21.1.x")
+  set(CLANG_VERSION_UPPER_BOUND 22.0.0)
   set(LLD_MIN_SUPPORTED 18.0)
-  set(LLD_MAX_SUPPORTED "20.1.x")
-  set(LLD_VERSION_UPPER_BOUND 21.0.0)
+  set(LLD_MAX_SUPPORTED "21.1.x")
+  set(LLD_VERSION_UPPER_BOUND 22.0.0)
   set(LLVM_MIN_SUPPORTED 18.0)
-  set(LLVM_MAX_SUPPORTED "20.1.x")
-  set(LLVM_VERSION_UPPER_BOUND 21.0.0)
+  set(LLVM_MAX_SUPPORTED "21.1.x")
+  set(LLVM_VERSION_UPPER_BOUND 22.0.0)
 
   ## Set Cmake packages search order
 
diff --git a/lib/CppInterOp/Compatibility.h b/lib/CppInterOp/Compatibility.h
index 562b42b38..f91bca070 100644
--- a/lib/CppInterOp/Compatibility.h
+++ b/lib/CppInterOp/Compatibility.h
@@ -27,6 +27,17 @@ static inline char* GetEnv(const char* Var_Name) {
 #endif
 }
 
+#if CLANG_VERSION_MAJOR < 21
+#define clang_LookupResult_Found clang::LookupResult::Found
+#define clang_LookupResult_Not_Found clang::LookupResult::NotFound
+#define clang_LookupResult_Found_Overloaded clang::LookupResult::FoundOverloaded
+#else
+#define clang_LookupResult_Found clang::LookupResultKind::Found
+#define clang_LookupResult_Not_Found clang::LookupResultKind::NotFound
+#define clang_LookupResult_Found_Overloaded                                    \
+  clang::LookupResultKind::FoundOverloaded
+#endif
+
 #if CLANG_VERSION_MAJOR < 19
 #define Template_Deduction_Result Sema::TemplateDeductionResult
 #define Template_Deduction_Result_Success                                      \
diff --git a/lib/CppInterOp/CppInterOp.cpp b/lib/CppInterOp/CppInterOp.cpp
index 56add4d8d..d289a46cf 100755
--- a/lib/CppInterOp/CppInterOp.cpp
+++ b/lib/CppInterOp/CppInterOp.cpp
@@ -1107,16 +1107,16 @@ bool GetClassTemplatedMethods(const std::string& name, TCppScope_t parent,
   auto* DC = clang::Decl::castToDeclContext(D);
   Cpp_utils::Lookup::Named(&S, R, DC);
 
-  if (R.getResultKind() == clang::LookupResult::NotFound && funcs.empty())
+  if (R.getResultKind() == clang_LookupResult_Not_Found && funcs.empty())
     return false;
 
   // Distinct match, single Decl
-  else if (R.getResultKind() == clang::LookupResult::Found) {
+  else if (R.getResultKind() == clang_LookupResult_Found) {
     if (IsTemplatedFunction(R.getFoundDecl()))
       funcs.push_back(R.getFoundDecl());
   }
   // Loop over overload set
-  else if (R.getResultKind() == clang::LookupResult::FoundOverloaded) {
+  else if (R.getResultKind() == clang_LookupResult_Found_Overloaded) {
     for (auto* Found : R)
       if (IsTemplatedFunction(Found))
         funcs.push_back(Found);
diff --git a/lib/CppInterOp/exports.ld b/lib/CppInterOp/exports.ld
index 49b7b0d83..65c3b439b 100644
--- a/lib/CppInterOp/exports.ld
+++ b/lib/CppInterOp/exports.ld
@@ -50,4 +50,6 @@
 -Wl,--export=_ZNK5clang4Type14isFloatingTypeEv
 -Wl,--export=_ZNK5clang12FunctionDecl12getNumParamsEv
 -Wl,--export=__clang_Interpreter_SetValueNoAlloc
--Wl,--export=__clang_Interpreter_SetValueWithAlloc
\ No newline at end of file
+-Wl,--export=__clang_Interpreter_SetValueWithAlloc
+-Wl,--export=_ZN5clang11Interpreter6createENSt3__210unique_ptrINS_16CompilerInstanceENS1_14default_deleteIS3_EEEENS2_IN4llvm3orc12LLJITBuilderENS4_IS9_EEEE
+-Wl,--export=_ZNK5clang13CXXRecordDecl19isInjectedClassNameEv
diff --git a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
new file mode 100644
index 000000000..00e0aef6f
--- /dev/null
+++ b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
@@ -0,0 +1,20 @@
+diff --git a/llvm/cmake/modules/CrossCompile.cmake b/llvm/cmake/modules/CrossCompile.cmake
+index 39b4abaa0..474ceddbb 100644
+--- a/llvm/cmake/modules/CrossCompile.cmake
++++ b/llvm/cmake/modules/CrossCompile.cmake
+@@ -74,10 +74,12 @@ function(llvm_create_cross_target project_name target_name toolchain buildtype)
+   endif()
+ 
+   add_custom_command(OUTPUT ${${project_name}_${target_name}_BUILD}/CMakeCache.txt
+-    COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}"
++    COMMAND ${CMAKE_COMMAND} -G Ninja
+         "-DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}"
+-        "-DCMAKE_C_COMPILER_LAUNCHER=${CMAKE_C_COMPILER_LAUNCHER}"
+-        "-DCMAKE_CXX_COMPILER_LAUNCHER=${CMAKE_CXX_COMPILER_LAUNCHER}"
++        -DCMAKE_C_COMPILER="clang-cl"
++        -DCMAKE_CXX_COMPILER="clang-cl"
++        -DCMAKE_ASM_MASM_COMPILER=llvm-ml
++        -DCMAKE_ASM_MASM_FLAGS="-m64"
+         ${CROSS_TOOLCHAIN_FLAGS_${target_name}} ${CMAKE_CURRENT_SOURCE_DIR}
+         ${CROSS_TOOLCHAIN_FLAGS_${project_name}_${target_name}}
+         -DLLVM_TARGET_IS_CROSSCOMPILE_HOST=TRUE
diff --git a/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch b/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
new file mode 100644
index 000000000..32ac45c13
--- /dev/null
+++ b/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
@@ -0,0 +1,15 @@
+diff --git a/clang/lib/Interpreter/Wasm.cpp b/clang/lib/Interpreter/Wasm.cpp
+index aa10b160ccf8..184867e2b55f 100644
+--- a/clang/lib/Interpreter/Wasm.cpp
++++ b/clang/lib/Interpreter/Wasm.cpp
+@@ -76,8 +76,8 @@ llvm::Error WasmIncrementalExecutor::addModule(PartialTranslationUnit &PTU) {
+   llvm::TargetMachine *TargetMachine = Target->createTargetMachine(
+       PTU.TheModule->getTargetTriple(), "", "", TO, llvm::Reloc::Model::PIC_);
+   PTU.TheModule->setDataLayout(TargetMachine->createDataLayout());
+-  std::string ObjectFileName = PTU.TheModule->getName().str() + ".o";
+-  std::string BinaryFileName = PTU.TheModule->getName().str() + ".wasm";
++  std::string ObjectFileName = "/tmp/" + PTU.TheModule->getName().str() + ".o";
++  std::string BinaryFileName = "/tmp/" + PTU.TheModule->getName().str() + ".wasm";
+ 
+   std::error_code Error;
+   llvm::raw_fd_ostream ObjectFileOutput(llvm::StringRef(ObjectFileName), Error);