diff --git a/.github/workflows/build-llvm-nightly.yml b/.github/workflows/build-llvm-nightly.yml
index 3912cdc7..7dca21fa 100644
--- a/.github/workflows/build-llvm-nightly.yml
+++ b/.github/workflows/build-llvm-nightly.yml
@@ -27,10 +27,10 @@ jobs:
       - run: nproc
       - run: wget https://apt.llvm.org/llvm.sh
       - run: chmod +x llvm.sh
-      - run: ./llvm.sh 20
-      - run: apt-get install -y bolt-20 clang-20 libclang-common-20-dev libclang-20-dev mlir-20-tools llvm-20-tools libclang-common-20-dev libclang-20-dev libclang1-20 clang-format-20 python3-clang-20 clangd-20 clang-tidy-20 libomp-20-dev
+      - run: ./llvm.sh 21
+      - run: apt-get install -y bolt-21 clang-21 libclang-common-21-dev libclang-21-dev mlir-21-tools llvm-21-tools libclang-common-21-dev libclang-21-dev libclang1-21 clang-format-21 python3-clang-21 clangd-21 clang-tidy-21 libomp-21-dev
       # TODO: remove in the future
-      - run: touch /usr/lib/llvm-20/lib/libLibcTableGenUtil.a
+      - run: touch /usr/lib/llvm-21/lib/libLibcTableGenUtil.a
       - uses: actions/checkout@v4
       - run: mkdir objdir
       - run: cmake ..
diff --git a/clang_delta/CommonRenameClassRewriteVisitor.h b/clang_delta/CommonRenameClassRewriteVisitor.h
index b758df79..598493b1 100644
--- a/clang_delta/CommonRenameClassRewriteVisitor.h
+++ b/clang_delta/CommonRenameClassRewriteVisitor.h
@@ -368,7 +368,12 @@ template<typename T> bool CommonRenameClassRewriteVisitor<T>::
     dyn_cast<DependentTemplateSpecializationType>(Ty);
   TransAssert(DTST && "Bad DependentTemplateSpecializationType!");
 
-  const IdentifierInfo *IdInfo = DTST->getIdentifier();
+  const IdentifierInfo *IdInfo =
+#if LLVM_VERSION_MAJOR > 20
+    DTST->getDependentTemplateName().getName().getIdentifier();
+#else
+    DTST->getIdentifier();
+#endif
   std::string IdName = IdInfo->getName().str();
   std::string Name;
   if (getNewNameByName(IdName, Name)) {
diff --git a/clang_delta/RemoveNamespace.cpp b/clang_delta/RemoveNamespace.cpp
index 20d234ee..ba816b07 100644
--- a/clang_delta/RemoveNamespace.cpp
+++ b/clang_delta/RemoveNamespace.cpp
@@ -440,7 +440,12 @@ bool RemoveNamespaceRewriteVisitor::VisitDependentTemplateSpecializationTypeLoc(
     dyn_cast<DependentTemplateSpecializationType>(Ty);
   TransAssert(DTST && "Bad DependentTemplateSpecializationType!");
 
-  const IdentifierInfo *IdInfo = DTST->getIdentifier();
+  const IdentifierInfo *IdInfo =
+#if LLVM_VERSION_MAJOR > 20
+    DTST->getDependentTemplateName().getName().getIdentifier();
+#else
+    DTST->getIdentifier();
+#endif
   std::string IdName = IdInfo->getName().str();
   std::string Name;
 
@@ -563,7 +568,9 @@ bool RemoveNamespaceRewriteVisitor::TraverseNestedNameSpecifierLoc(
         break;
       }
       case NestedNameSpecifier::TypeSpec: // Fall-through
+#if LLVM_VERSION_MAJOR <= 20
       case NestedNameSpecifier::TypeSpecWithTemplate:
+#endif
         TraverseTypeLoc(Loc.getTypeLoc());
         break;
       default:
diff --git a/clang_delta/RemoveUnusedFunction.cpp b/clang_delta/RemoveUnusedFunction.cpp
index ca9d3f7b..9b0c9651 100644
--- a/clang_delta/RemoveUnusedFunction.cpp
+++ b/clang_delta/RemoveUnusedFunction.cpp
@@ -254,7 +254,11 @@ bool RUFAnalysisVisitor::VisitFunctionDecl(FunctionDecl *FD)
 
   if (FD->isReferenced() ||
       FD->isMain() ||
+#if LLVM_VERSION_MAJOR > 20
+      FD->hasAttr<DeviceKernelAttr>() ||
+#else
       FD->hasAttr<OpenCLKernelAttr>() ||
+#endif
       ConsumerInstance->hasReferencedSpecialization(CanonicalFD) ||
       ConsumerInstance->isInlinedSystemFunction(CanonicalFD) ||
       ConsumerInstance->isInReferencedSet(CanonicalFD) ||
diff --git a/clang_delta/RenameFun.cpp b/clang_delta/RenameFun.cpp
index 8dee2431..2a4b0ae6 100644
--- a/clang_delta/RenameFun.cpp
+++ b/clang_delta/RenameFun.cpp
@@ -261,7 +261,13 @@ void RenameFun::addFun(const FunctionDecl *FD)
 {
   std::string Name = FD->getNameAsString();
   // Skip special functions
-  if (isSpecialFun(Name) || FD->hasAttr<OpenCLKernelAttr>())
+  if (isSpecialFun(Name) ||
+#if LLVM_VERSION_MAJOR > 20
+      FD->hasAttr<DeviceKernelAttr>()
+#else
+      FD->hasAttr<OpenCLKernelAttr>()
+#endif
+     )
     FunToNameMap[FD] = Name;
 
   if (FunToNameMap.find(FD) != FunToNameMap.end())
diff --git a/clang_delta/Transformation.cpp b/clang_delta/Transformation.cpp
index d4896cb9..0da9827a 100644
--- a/clang_delta/Transformation.cpp
+++ b/clang_delta/Transformation.cpp
@@ -675,7 +675,10 @@ const DeclContext *Transformation::getDeclContextFromSpecifier(
         return NAD->getNamespace()->getCanonicalDecl();
       }
       case NestedNameSpecifier::TypeSpec: // Fall-through
-      case NestedNameSpecifier::TypeSpecWithTemplate: {
+#if LLVM_VERSION_MAJOR <= 20
+      case NestedNameSpecifier::TypeSpecWithTemplate:
+#endif
+      {
         const Type *Ty = NNS->getAsType();
         if (const RecordType *RT = Ty->getAs<RecordType>())
           return RT->getDecl();
diff --git a/clang_delta/TransformationManager.cpp b/clang_delta/TransformationManager.cpp
index d985bd51..d36f62a5 100644
--- a/clang_delta/TransformationManager.cpp
+++ b/clang_delta/TransformationManager.cpp
@@ -163,7 +163,12 @@ bool TransformationManager::initializeCompilerInstance(std::string &ErrorMsg)
     ClangInstance->createFileManager();
 
     if(CLCPath != NULL && ClangInstance->hasFileManager() &&
-       ClangInstance->getFileManager().getDirectory(CLCPath, false)) {
+#if LLVM_VERSION_MAJOR > 20
+       ClangInstance->getFileManager().getDirectoryRef(CLCPath, false)
+#else
+       ClangInstance->getFileManager().getDirectory(CLCPath, false)
+#endif
+      ) {
         Args.push_back("-I");
         Args.push_back(CLCPath);
     }
@@ -186,7 +191,12 @@ bool TransformationManager::initializeCompilerInstance(std::string &ErrorMsg)
 
   TargetInfo *Target = 
     TargetInfo::CreateTargetInfo(ClangInstance->getDiagnostics(),
-                                 ClangInstance->getInvocation().TargetOpts);
+#if LLVM_VERSION_MAJOR > 20
+                                 ClangInstance->getInvocation().getTargetOpts()
+#else
+                                 ClangInstance->getInvocation().TargetOpts
+#endif
+                                );
   ClangInstance->setTarget(Target);
 
   if (const char *env = getenv("CVISE_INCLUDE_PATH")) {