diff --git a/clang-uml-clang21.patch b/clang-uml-clang21.patch
new file mode 100644
index 00000000000..256a27700ae
--- /dev/null
+++ b/clang-uml-clang21.patch
@@ -0,0 +1,32 @@
+diff --git a/tests/test_clang_util.cc b/tests/test_clang_util.cc
+index 3197efa..2117824 100644
+--- a/tests/test_clang_util.cc
++++ b/tests/test_clang_util.cc
+@@ -144,14 +144,14 @@ TEST_CASE("Test diagnostic_consumer")
+     auto fs = llvm::vfs::getRealFileSystem();
+     FileSystemOptions file_opts;
+     FileManager file_mgr(file_opts, fs);
+-    auto diagnostic_engine = DiagnosticsEngine(
+-        llvm::IntrusiveRefCntPtr<DiagnosticIDs>(new DiagnosticIDs()),
+-        new DiagnosticOptions());
++    auto diagIDs1 = llvm::makeIntrusiveRefCnt<clang::DiagnosticIDs>();
++    clang::DiagnosticOptions diagOpts1;
++    auto diagnostic_engine = clang::DiagnosticsEngine(diagIDs1, diagOpts1);
+     SourceManager source_mgr(diagnostic_engine, file_mgr);
+ 
+-    DiagnosticsEngine diag_engine(
+-        llvm::IntrusiveRefCntPtr<DiagnosticIDs>(new DiagnosticIDs()),
+-        new DiagnosticOptions());
++    auto diagIDs2 = llvm::makeIntrusiveRefCnt<clang::DiagnosticIDs>();
++    clang::DiagnosticOptions diagOpts2;
++    clang::DiagnosticsEngine diag_engine(diagIDs2, diagOpts2);
+ 
+     diag_engine.setClient(&consumer, false);
+     auto id_note = diag_engine.getCustomDiagID(
+@@ -198,4 +198,4 @@ TEST_CASE("Test diagnostic_consumer")
+     CHECK(consumer.diagnostics.size() == 4);
+     CHECK(consumer.diagnostics[3].level == DiagnosticsEngine::Fatal);
+     CHECK(consumer.diagnostics[3].description == "test fatal message");
+-}
+\ No newline at end of file
++}
diff --git a/clang-uml-yamlcpp.patch b/clang-uml-yamlcpp.patch
new file mode 100644
index 00000000000..d149836c5b9
--- /dev/null
+++ b/clang-uml-yamlcpp.patch
@@ -0,0 +1,18 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index aad3092..839a8f6 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -145,12 +145,7 @@ find_package(yaml-cpp REQUIRED)
+ if(MSVC)
+     add_definitions(-DYAML_CPP_STATIC_DEFINE)
+ endif(MSVC)
+-if(APPLE)
+-    set(YAML_CPP_LIBRARIES yaml-cpp::yaml-cpp)
+-endif(APPLE)
+-if(LINUX)
+-    set(YAML_CPP_LIBRARIES yaml-cpp)
+-endif(LINUX)
++set(YAML_CPP_LIBRARIES yaml-cpp::yaml-cpp)
+ message(STATUS "Found yaml-cpp at: ${YAML_CPP_INCLUDE_DIR}, library: ${YAML_CPP_LIBRARIES}")
+ 
+ #
diff --git a/clang-uml.spec b/clang-uml.spec
index e9e5acc4b1d..3d6eed29cde 100644
--- a/clang-uml.spec
+++ b/clang-uml.spec
@@ -1,15 +1,19 @@
-### RPM external clang-uml 0.5.2
+### RPM external clang-uml 0.6.2x
 
-%define tag cd6dce2b0b34d55534d3de512ab088b9ad71bc76
+%define tag 5e2993e75ebc88af6cb239f2ffae88da7431cb0d
 %define branch master
 
 %define github_user bkryza
 Source: git+https://github.com/%{github_user}/clang-uml.git?obj=%{branch}/%{tag}&export=%{n}-%{realversion}&output=/%{n}-%{realversion}-%{tag}.tgz
+Patch0: clang-uml-clang21
+Patch1: clang-uml-yamlcpp
 BuildRequires: cmake ninja 
 Requires: yaml-cpp llvm zlib
 
 %prep
 %setup -n %{n}-%{realversion}
+%patch0 -p1
+%patch1 -p1
 
 %build
 rm -rf ../build
@@ -28,7 +32,7 @@ cmake ../%{n}-%{realversion} \
   -DCMAKE_CXX_FLAGS="-Wno-sign-compare" \
 %endif
   -DGIT_VERSION="%{realversion}" \
-  -DCMAKE_PREFIX_PATH="${YAML_CPP_ROOT}/lib64/cmake/yaml-cpp;${ZLIB_ROOT}"
+  -DCMAKE_PREFIX_PATH="${YAML_CPP_ROOT};${ZLIB_ROOT}"
 
 ninja -v %{makeprocesses}
 
diff --git a/llvm.spec b/llvm.spec
index fa90adec9de..f599a2a236b 100644
--- a/llvm.spec
+++ b/llvm.spec
@@ -1,4 +1,5 @@
-### RPM external llvm 18.1.6
+### RPM external llvm 21.1.4
+
 ## INITENV +PATH LD_LIBRARY_PATH %{i}/lib64
 ## INITENV +PATH PYTHON3PATH %{i}/lib64/python%{cms_python3_major_minor_version}/site-packages
 
@@ -6,20 +7,17 @@ BuildRequires: cmake ninja
 Requires: gcc zlib python3 libxml2 zstd libunwind
 %{!?without_cuda:Requires: cuda}
 
-%define llvmCommit 02c7568fc9f555b2c72fc169c8c68e2116d97382
-%define llvmBranch cms/release/18.x/1118c2e
-%define iwyuCommit 377eaef70cdda47368939f4d9beabfabe3f628f0
-%define iwyuBranch clang_18
+%define llvmCommit 3063d23cfa249166b2e0c33a02c7300c20ffb2d
+%define llvmBranch cms/llvmorg-21.1.4
+%define iwyuCommit 791e69ea4662cb3e74e8128fd5fd69bd7f4ea6b3
+%define iwyuBranch clang_21
 
 Source0: git+https://github.com/cms-externals/llvm-project.git?obj=%{llvmBranch}/%{llvmCommit}&export=llvm-%{realversion}-%{llvmCommit}&module=llvm-%{realversion}-%{llvmCommit}&output=/llvm-%{realversion}-%{llvmCommit}.tgz
 Source1: git+https://github.com/include-what-you-use/include-what-you-use.git?obj=%{iwyuBranch}/%{iwyuCommit}&export=iwyu-%{realversion}-%{iwyuCommit}&module=iwyu-%{realversion}-%{iwyuCommit}&output=/iwyu-%{realversion}-%{iwyuCommit}.tgz
-# GCC 15 fix: include cstdint
-Patch0: llvm-gcc15
 %define keep_archives true
 
 %prep
 %setup -T -b0 -n llvm-%{realversion}-%{llvmCommit}
-%patch0 -p1
 
 # include-what-you-see is not LLVM project, we add it explicitly to the clang tools
 %setup -T -D -a1 -c -n llvm-%{realversion}-%{llvmCommit}/clang/tools
diff --git a/mozsearch-clang21.patch b/mozsearch-clang21.patch
new file mode 100644
index 00000000000..bbd92ca7cf2
--- /dev/null
+++ b/mozsearch-clang21.patch
@@ -0,0 +1,62 @@
+diff --git a/clang-plugin/MozsearchIndexer.cpp b/clang-plugin/MozsearchIndexer.cpp
+index a601b05..380cbcd 100644
+--- a/clang-plugin/MozsearchIndexer.cpp
++++ b/clang-plugin/MozsearchIndexer.cpp
+@@ -1485,7 +1485,9 @@ public:
+       QualType CanonicalFieldType = FieldType.getCanonicalType();
+       LangOptions langOptions;
+       PrintingPolicy Policy(langOptions);
++#if LLVM_VERSION_MAJOR < 21
+       Policy.PrintCanonicalTypes = true;
++#endif
+       J.attribute("type", CanonicalFieldType.getAsString(Policy));
+ 
+       const TagDecl *tagDecl = CanonicalFieldType->getAsTagDecl();
+diff --git a/clang-plugin/from-clangd/HeuristicResolver.cpp b/clang-plugin/from-clangd/HeuristicResolver.cpp
+index 719094d..54184a4 100644
+--- a/clang-plugin/from-clangd/HeuristicResolver.cpp
++++ b/clang-plugin/from-clangd/HeuristicResolver.cpp
+@@ -27,7 +27,7 @@ const auto StaticFilter = [](const NamedDecl *D) {
+ };
+ const auto ValueFilter = [](const NamedDecl *D) { return isa<ValueDecl>(D); };
+ const auto TypeFilter = [](const NamedDecl *D) { return isa<TypeDecl>(D); };
+-const auto TemplateFilter = [](const NamedDecl *D) {
++[[maybe_unused]] const auto TemplateFilter = [](const NamedDecl *D) {
+   return isa<TemplateDecl>(D);
+ };
+ 
+@@ -203,12 +203,22 @@ std::vector<const NamedDecl *> HeuristicResolver::resolveDependentNameType(
+       DNT->getIdentifier(), TypeFilter);
+ }
+ 
++
++#include "clang/Basic/Version.h"
+ std::vector<const NamedDecl *>
+ HeuristicResolver::resolveTemplateSpecializationType(
+     const DependentTemplateSpecializationType *DTST) const {
++#if LLVM_VERSION_MAJOR >= 21
++    // In LLVM 21+, DependentTemplateSpecializationType no longer exposes
++    // getQualifier(), getIdentifier(), or getTemplateName().
++    // We can’t meaningfully resolve it here — return an empty result.
++    return {};
++#else
++  // Legacy LLVM ≤ 20 path.
+   return resolveDependentMember(
+       resolveNestedNameSpecifierToType(DTST->getQualifier()),
+       DTST->getIdentifier(), TemplateFilter);
++#endif
+ }
+ 
+ std::vector<const NamedDecl *>
+@@ -249,8 +259,11 @@ const Type *HeuristicResolver::resolveNestedNameSpecifierToType(
+   // that may be dependent as well, so for convenience handle
+   // the TypeSpec cases too.
+   switch (NNS->getKind()) {
++#if LLVM_VERSION_MAJOR >= 21
+   case NestedNameSpecifier::TypeSpec:
++#else
+   case NestedNameSpecifier::TypeSpecWithTemplate:
++#endif
+     return NNS->getAsType();
+   case NestedNameSpecifier::Identifier: {
+     return resolveDeclsToType(
diff --git a/mozsearch.spec b/mozsearch.spec
index d8b3b2b2bff..2d5e7622eb2 100644
--- a/mozsearch.spec
+++ b/mozsearch.spec
@@ -1,17 +1,19 @@
-### RPM external mozsearch 20240514
+### RPM external mozsearch 20251022
 
-%define tag d697005b97f28d493a24887ed25fd2e68839c716
+%define tag 1c886cc95c4e811709e97f711d7691ff8b87bda9
 %define branch master
 
 %define github_user mozsearch
 Source: git+https://github.com/%{github_user}/%{n}.git?obj=%{branch}/%{tag}&export=%{n}-%{realversion}&output=/%{n}-%{realversion}-%{tag}.tgz
 Patch0: mozsearch-gcc-toolchain
+Patch1: mozsearch-clang21
 BuildRequires: gmake
 Requires: llvm
 
 %prep
 %setup -n %{n}-%{realversion}
 %patch0 -p1
+%patch1 -p1
 
 %build
 cd clang-plugin
diff --git a/py3-dxr.spec b/py3-dxr.spec
index 87a41a0335a..4b2427a5d4e 100644
--- a/py3-dxr.spec
+++ b/py3-dxr.spec
@@ -2,8 +2,8 @@
 ## INITENV +PATH PYTHON3PATH %i/${PYTHON3_LIB_SITE_PACKAGES}
 Requires: zlib llvm sqlite
 Requires: py3-Jinja2 py3-parsimonious py3-pysqlite3 py3-Pygments
-%define dxrCommit 737d3b0570e5e4a7845e8cba7c0b000d2911f24e
-%define branch cms/6ea764102a/clang18
+%define dxrCommit b55cf0eeacc494adc575562eac290b3e4871a6ac
+%define branch cms/clang21
 
 Source0: git+https://github.com/cms-externals/dxr.git?obj=%{branch}/%{dxrCommit}&export=dxr-%{dxrCommit}&module=dxr-%dxrCommit&output=/dxr-%{dxrCommit}.tgz
 %define keep_archives true