diff --git a/Aliases/lld@21 b/Aliases/lld@21
new file mode 120000
index 0000000000000..789ca30241210
--- /dev/null
+++ b/Aliases/lld@21
@@ -0,0 +1 @@
+../Formula/l/lld.rb
\ No newline at end of file
diff --git a/Aliases/llvm@21 b/Aliases/llvm@21
new file mode 120000
index 0000000000000..5251b0d981566
--- /dev/null
+++ b/Aliases/llvm@21
@@ -0,0 +1 @@
+../Formula/l/llvm.rb
\ No newline at end of file
diff --git a/Formula/a/adaptivecpp.rb b/Formula/a/adaptivecpp.rb
index db9c630c69c7f..6d75ee8aca82e 100644
--- a/Formula/a/adaptivecpp.rb
+++ b/Formula/a/adaptivecpp.rb
@@ -1,11 +1,21 @@
 class Adaptivecpp < Formula
   desc "SYCL and C++ standard parallelism for CPUs and GPUs"
   homepage "https://adaptivecpp.github.io/"
-  url "https://github.com/AdaptiveCpp/AdaptiveCpp/archive/refs/tags/v25.02.0.tar.gz"
-  sha256 "8cc8a3be7bb38f88d7fd51597e0ec924b124d4233f64da62a31b9945b55612ca"
   license "BSD-2-Clause"
+  revision 1
   head "https://github.com/AdaptiveCpp/AdaptiveCpp.git", branch: "develop"
 
+  stable do
+    url "https://github.com/AdaptiveCpp/AdaptiveCpp/archive/refs/tags/v25.02.0.tar.gz"
+    sha256 "8cc8a3be7bb38f88d7fd51597e0ec924b124d4233f64da62a31b9945b55612ca"
+
+    # Backport support for LLVM 21
+    patch do
+      url "https://github.com/AdaptiveCpp/AdaptiveCpp/commit/623aa0b1840c5ccd7a45d3e8b228f1bff5257056.patch?full_index=1"
+      sha256 "d3b8708ded954f04b87ad22254fd949c1d584d6de7a3f8a7e978ff715ca1a33d"
+    end
+  end
+
   bottle do
     sha256 arm64_sequoia: "fa1c355b2af0934de4aae2fdb882f7befae852e5523ed4b3f4270d69bfd46edf"
     sha256 arm64_sonoma:  "c01a61e3a4629d1c1c52ba7d9f5f0618f6b7f6a246d25da96c4e0ed481f0b6bc"
diff --git a/Formula/a/afl++.rb b/Formula/a/afl++.rb
index c0af0ad51a485..cda3e9cfb2865 100644
--- a/Formula/a/afl++.rb
+++ b/Formula/a/afl++.rb
@@ -5,6 +5,7 @@ class Aflxx < Formula
   version "4.33c"
   sha256 "98903c8036282c8908b1d8cc0d60caf3ea259db4339503a76449b47acce58d1d"
   license "Apache-2.0"
+  revision 1
 
   livecheck do
     url :stable
diff --git a/Formula/a/alive2.rb b/Formula/a/alive2.rb
index f47a2b282ce3f..ec2d7926c6ce0 100644
--- a/Formula/a/alive2.rb
+++ b/Formula/a/alive2.rb
@@ -5,6 +5,7 @@ class Alive2 < Formula
       tag:      "v21.0",
       revision: "913e1556032ee70a9ebf147b5a0c7e10086b7490"
   license "MIT"
+  revision 1
   head "https://github.com/AliveToolkit/alive2.git", branch: "master"
 
   bottle do
@@ -28,7 +29,12 @@ class Alive2 < Formula
   def install
     # Work around ir/state.cpp:730:40: error: reference to local binding
     # 'src_data' declared in enclosing function 'IR::State::copyUBFromBB'
-    ENV.llvm_clang if OS.mac? && MacOS.version <= :ventura
+    if OS.mac? && MacOS.version <= :ventura
+      ENV.llvm_clang
+      # Also link to LLVM libc++ due to `std::__hash_memory` availability in newer header
+      # https://github.com/llvm/llvm-project/commit/17d05695388128353662fbb80bbb7a13d172b41d
+      ENV.prepend "LDFLAGS", "-L#{Formula["llvm"].opt_lib}/c++ -L#{Formula["llvm"].opt_lib}/unwind -lunwind"
+    end
 
     system "cmake", "-S", ".", "-B", "build", "-DBUILD_LLVM_UTILS=ON", "-DBUILD_TV=ON", *std_cmake_args
     system "cmake", "--build", "build"
diff --git a/Formula/c/castxml.rb b/Formula/c/castxml.rb
index fac29f711c4fc..c3767d01b80fd 100644
--- a/Formula/c/castxml.rb
+++ b/Formula/c/castxml.rb
@@ -1,12 +1,25 @@
 class Castxml < Formula
   desc "C-family Abstract Syntax Tree XML Output"
   homepage "https://github.com/CastXML/CastXML"
-  url "https://github.com/CastXML/CastXML/archive/refs/tags/v0.6.11.tar.gz"
-  sha256 "fc5b49f802b67f98ecea10564bc171c660020836a48cecefc416681a2d2e1d3d"
   license "Apache-2.0"
-  revision 1
+  revision 2
   head "https://github.com/CastXML/castxml.git", branch: "master"
 
+  stable do
+    url "https://github.com/CastXML/CastXML/archive/refs/tags/v0.6.11.tar.gz"
+    sha256 "fc5b49f802b67f98ecea10564bc171c660020836a48cecefc416681a2d2e1d3d"
+
+    # Backport support for LLVM 21
+    patch do
+      url "https://github.com/CastXML/CastXML/commit/f4fdb9eebe3a03c8c6479a1cf420761a97e86824.patch?full_index=1"
+      sha256 "33093a62dc22f98ab1f6b44a1eca7a668bc142e870069ea51fa5bbd44627dcae"
+    end
+    patch do
+      url "https://github.com/CastXML/CastXML/commit/e71d56d34d308f410ac6f5493c5622e9701e210f.patch?full_index=1"
+      sha256 "cab3ccec1795d8228a5f784c88b23846e2a90415d084513e9b8f237759a68da6"
+    end
+  end
+
   livecheck do
     url :stable
     regex(/^v?(\d+(?:\.\d+)+)$/i)
diff --git a/Formula/c/ccls.rb b/Formula/c/ccls.rb
index 6478db745bd67..993db805d367a 100644
--- a/Formula/c/ccls.rb
+++ b/Formula/c/ccls.rb
@@ -7,7 +7,7 @@ class Ccls < Formula
   #       https://github.com/MaskRay/ccls/issues/786
   #       https://github.com/MaskRay/ccls/issues/895
   license "Apache-2.0"
-  revision 1
+  revision 2
   head "https://github.com/MaskRay/ccls.git", branch: "master"
 
   stable do
@@ -19,6 +19,22 @@ class Ccls < Formula
       url "https://github.com/MaskRay/ccls/commit/4331c8958698d42933bf4e132f8a7d61f3cedb8c.patch?full_index=1"
       sha256 "5420b53cf912268688953a2863e86f6b88334ed548852eaedb9f8ce4871ee034"
     end
+
+    # Backport reformat commit to cleanly apply later patches
+    patch do
+      url "https://github.com/MaskRay/ccls/commit/48f1a006b78944a944cdc0c98fb4b447e19fce7d.patch?full_index=1"
+      sha256 "2fa14b78e00b455138324034f876979f40c34e253b5b254ea794e60a38ac657b"
+    end
+
+    # Backport support for LLVM 21
+    patch do
+      url "https://github.com/MaskRay/ccls/commit/44fb405d00dead04de43891c9818d798f10fc41e.patch?full_index=1"
+      sha256 "40229b6bc013a6daf510b980a7b032bad159f43e95796467705042beeb70fe49"
+    end
+    patch do
+      url "https://github.com/MaskRay/ccls/commit/4427527ed8107719457b5260443e8cad024e446f.patch?full_index=1"
+      sha256 "16ba1cd3c18441054fcc54716e44e013ee01c21b25b796adc480620df511abe0"
+    end
   end
 
   bottle do
diff --git a/Formula/c/clang-uml.rb b/Formula/c/clang-uml.rb
index f8e11d294330b..0ef95af417c10 100644
--- a/Formula/c/clang-uml.rb
+++ b/Formula/c/clang-uml.rb
@@ -4,6 +4,7 @@ class ClangUml < Formula
   url "https://github.com/bkryza/clang-uml/archive/refs/tags/0.6.2.tar.gz"
   sha256 "004540c328699f81abebceb33a4661b548ab3a5f74096da2c025b9971b2b17ff"
   license "Apache-2.0"
+  revision 1
   head "https://github.com/bkryza/clang-uml.git", branch: "master"
 
   bottle do
diff --git a/Formula/c/clazy.rb b/Formula/c/clazy.rb
index abc8b7b365cb1..f7b28c9abcdd4 100644
--- a/Formula/c/clazy.rb
+++ b/Formula/c/clazy.rb
@@ -4,6 +4,7 @@ class Clazy < Formula
   url "https://download.kde.org/stable/clazy/1.15/src/clazy-1.15.tar.xz"
   sha256 "43189460b366ea3126242878c36ee8a403e37ec4baef7e61ccfa124b1414e7a9"
   license "LGPL-2.0-or-later"
+  revision 1
   head "https://invent.kde.org/sdk/clazy.git", branch: "master"
 
   livecheck do
diff --git a/Formula/c/crystal.rb b/Formula/c/crystal.rb
index dbba7b5b94d1e..caae7c7505000 100644
--- a/Formula/c/crystal.rb
+++ b/Formula/c/crystal.rb
@@ -2,6 +2,7 @@ class Crystal < Formula
   desc "Fast and statically typed, compiled language with Ruby-like syntax"
   homepage "https://crystal-lang.org/"
   license "Apache-2.0"
+  revision 1
 
   stable do
     # TODO: Replace arm64 linux bootstrap with official when available
@@ -12,6 +13,12 @@ class Crystal < Formula
       url "https://github.com/crystal-lang/shards/archive/refs/tags/v0.19.1.tar.gz"
       sha256 "2a49e7ffa4025e0b3e8774620fa8dbc227d3d1e476211fefa2e8166dcabf82b5"
     end
+
+    # Backport support for LLVM 21
+    patch do
+      url "https://github.com/crystal-lang/crystal/commit/0e3757edcf7f18c238841e2f2aa659ac302fee4a.patch?full_index=1"
+      sha256 "8f5f9682990a74405f7bbae3b20afcf6bd11f65826204fee77b52b69d0c34925"
+    end
   end
 
   livecheck do
diff --git a/Formula/c/crystalline.rb b/Formula/c/crystalline.rb
index e609bf16212ea..c6b945e168a08 100644
--- a/Formula/c/crystalline.rb
+++ b/Formula/c/crystalline.rb
@@ -4,6 +4,7 @@ class Crystalline < Formula
   url "https://github.com/elbywan/crystalline/archive/refs/tags/v0.17.1.tar.gz"
   sha256 "3e8f4c3f41830092300219ef91c3d03e15536774ef18a5395ff6a9fffc27be5b"
   license "MIT"
+  revision 1
 
   bottle do
     sha256 arm64_sequoia: "87a66475cc7c310d5a9ca86451588753fa013793a29647adc860a722d44262b3"
diff --git a/Formula/e/enzyme.rb b/Formula/e/enzyme.rb
index af2d8c2db7530..1ecd5c27fb615 100644
--- a/Formula/e/enzyme.rb
+++ b/Formula/e/enzyme.rb
@@ -4,6 +4,7 @@ class Enzyme < Formula
   url "https://github.com/EnzymeAD/Enzyme/archive/refs/tags/v0.0.191.tar.gz"
   sha256 "5832f70fdbebc922c45da9e1d49985d96b91d54d12eac8e3f96aee9d3b09eb86"
   license "Apache-2.0" => { with: "LLVM-exception" }
+  revision 1
   head "https://github.com/EnzymeAD/Enzyme.git", branch: "main"
 
   bottle do
diff --git a/Formula/f/flang.rb b/Formula/f/flang.rb
index f80026c49a8db..ba0d693c39e8c 100644
--- a/Formula/f/flang.rb
+++ b/Formula/f/flang.rb
@@ -1,8 +1,8 @@
 class Flang < Formula
   desc "LLVM Fortran Frontend"
   homepage "https://flang.llvm.org/"
-  url "https://github.com/llvm/llvm-project/releases/download/llvmorg-20.1.8/llvm-project-20.1.8.src.tar.xz"
-  sha256 "6898f963c8e938981e6c4a302e83ec5beb4630147c7311183cf61069af16333d"
+  url "https://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.0-rc3/llvm-project-21.1.0-rc3.src.tar.xz"
+  sha256 "7c61598f3902e61499b4a8d0302087ed2421c75bf504d084f2e6fa5450ab94d7"
   # The LLVM Project is under the Apache License v2.0 with LLVM Exceptions
   license "Apache-2.0" => { with: "LLVM-exception" }
   head "https://github.com/llvm/llvm-project.git", branch: "main"
@@ -24,6 +24,9 @@ class Flang < Formula
   depends_on "cmake" => :build
   depends_on "llvm"
 
+  # Keep broken symlink if `llvm` has been unlinked on Linux.
+  skip_clean "lib/LLVMgold.so"
+
   # Building with GCC fails at linking with an obscure error.
   fails_with :gcc
 
@@ -32,68 +35,70 @@ def llvm
   end
 
   def install
-    # Generate omp_lib.h and omp_lib.F90 to be used by flang build
-    system "cmake", "-S", "openmp", "-B", "build/projects/openmp", *std_cmake_args
+    resource_dir = Pathname(Utils.safe_popen_read(llvm.opt_bin/"clang", "-print-resource-dir").chomp)
+    relative_resource_dir = resource_dir.relative_path_from(llvm.prefix.realpath)
+
+    common_args = %W[
+      -DBUILD_SHARED_LIBS=ON
+      -DLLVM_DIR=#{llvm.opt_lib}/cmake/llvm
+      -DLLVM_ENABLE_FATLTO=ON
+      -DLLVM_ENABLE_LTO=ON
+    ]
 
-    args = %W[
+    flang_args = %W[
       -DCLANG_DIR=#{llvm.opt_lib}/cmake/clang
       -DFLANG_INCLUDE_TESTS=OFF
       -DFLANG_REPOSITORY_STRING=#{tap&.issues_url}
       -DFLANG_VENDOR=#{tap&.user}
-      -DLLVM_DIR=#{llvm.opt_lib}/cmake/llvm
-      -DLLVM_ENABLE_FATLTO=ON
-      -DLLVM_ENABLE_LTO=ON
       -DLLVM_TOOL_OPENMP_BUILD=ON
       -DLLVM_USE_SYMLINKS=ON
       -DMLIR_DIR=#{llvm.opt_lib}/cmake/mlir
       -DMLIR_LINK_MLIR_DYLIB=ON
     ]
-    args << "-DFLANG_VENDOR_UTI=sh.brew.flang" if tap&.official?
-    # FIXME: Setting `BUILD_SHARED_LIBS=ON` causes the just-built flang to throw ICE on macOS
-    args << "-DBUILD_SHARED_LIBS=ON" if OS.linux?
+    flang_args << "-DFLANG_VENDOR_UTI=sh.brew.flang" if tap&.official?
+
+    flang_rt_args = %W[
+      -DCMAKE_Fortran_COMPILER_WORKS=ON
+      -DCMAKE_Fortran_COMPILER=#{bin}/flang
+      -DFLANG_RT_ENABLE_SHARED=ON
+      -DFLANG_RT_ENABLE_STATIC=OFF
+      -DFLANG_RT_INCLUDE_TESTS=OFF
+      -DLLVM_BINARY_DIR=#{llvm.opt_prefix}
+      -DLLVM_ENABLE_RUNTIMES=flang-rt
+    ]
+
+    # Generate omp_lib.h and omp_lib.F90 to be used by flang build
+    system "cmake", "-S", "openmp", "-B", "build/projects/openmp", *std_cmake_args
 
-    system "cmake", "-S", "flang", "-B", "build", *args, *std_cmake_args
+    system "cmake", "-S", "flang", "-B", "build", *flang_args, *common_args, *std_cmake_args
     system "cmake", "--build", "build"
     system "cmake", "--install", "build"
-    return if OS.linux?
+
+    system "cmake", "-S", "runtimes", "-B", "build-rt", *flang_rt_args, *common_args, *std_cmake_args
+    system "cmake", "--build", "build-rt"
+    system "cmake", "--install", "build-rt"
+
+    # Add symlink for runtime library as it won't be found when resource-dir is
+    # overridden by flang.cfg. This also allows shared `flang-rt` on Linux to
+    # avoid extra RPATH. See if the upstream provides a better way of handling:
+    # https://github.com/llvm/llvm-project/blob/main/flang-rt/CMakeLists.txt#L120-L130
+    lib.install_symlink (prefix/relative_resource_dir).glob("**/#{shared_library("*")}")
+
+    if OS.linux?
+      # Allow flang -flto to work on Linux as it expects library relative to driver.
+      # The HOMEBREW_PREFIX path is used so that `brew link` skips creating a symlink.
+      lib.install_symlink HOMEBREW_PREFIX/"lib/LLVMgold.so"
+      return
+    end
 
     libexec.install bin.children
     bin.install_symlink libexec.children
 
     # Help `flang` driver find `libLTO.dylib` and runtime libraries
-    resource_dir = Utils.safe_popen_read(llvm.opt_bin/"clang", "-print-resource-dir").chomp
-    resource_dir.gsub!(llvm.prefix.realpath, llvm.opt_prefix)
     (libexec/"flang.cfg").atomic_write <<~CONFIG
       -Wl,-lto_library,#{llvm.opt_lib}/libLTO.dylib
-      -resource-dir=#{resource_dir}
+      -resource-dir=#{llvm.opt_prefix/relative_resource_dir}
     CONFIG
-
-    # Convert LTO-generated bitcode in our static archives to MachO.
-    # Not needed on Linux because of `-ffat-lto-objects`
-    # See equivalent code in `llvm.rb`.
-    lib.glob("*.a").each do |static_archive|
-      mktemp do
-        system llvm.opt_bin/"llvm-ar", "x", static_archive
-        rebuilt_files = []
-
-        Pathname.glob("*.o").each do |bc_file|
-          file_type = Utils.safe_popen_read("file", "--brief", bc_file)
-          next unless file_type.match?(/^LLVM (IR )?bitcode/)
-
-          rebuilt_files << bc_file
-          system ENV.cc, "-fno-lto", "-Wno-unused-command-line-argument",
-                         "-x", "ir", bc_file, "-c", "-o", bc_file
-        end
-
-        system llvm.opt_bin/"llvm-ar", "r", static_archive, *rebuilt_files if rebuilt_files.present?
-      end
-    end
-  end
-
-  def post_install
-    # Allow flang -flto to work on Linux as it expects library relative to driver.
-    # The HOMEBREW_PREFIX path is used so that `brew link` skips creating a symlink.
-    lib.install_symlink HOMEBREW_PREFIX/"lib/LLVMgold.so" if OS.linux?
   end
 
   test do
@@ -159,13 +164,9 @@ def post_install
     system bin/"flang", "-v", "runtimes.f90"
 
     return if OS.linux?
+    return unless (etc/"clang").exist? # https://github.com/Homebrew/homebrew-test-bot/issues/805
 
     assert_match %r{^Configuration file: #{Regexp.escape(etc)}/clang/.*\.cfg$}i,
                  shell_output("#{bin}/flang --version")
-
-    system "ar", "x", lib/"libFortranCommon.a"
-    testpath.glob("*.o").each do |object_file|
-      refute_match(/LLVM (IR )?bitcode/, shell_output("file --brief #{object_file}"))
-    end
   end
 end
diff --git a/Formula/l/lld.rb b/Formula/l/lld.rb
index d1de9dd875eb0..b806728a11c0c 100644
--- a/Formula/l/lld.rb
+++ b/Formula/l/lld.rb
@@ -1,8 +1,8 @@
 class Lld < Formula
   desc "LLVM Project Linker"
   homepage "https://lld.llvm.org/"
-  url "https://github.com/llvm/llvm-project/releases/download/llvmorg-20.1.8/llvm-project-20.1.8.src.tar.xz"
-  sha256 "6898f963c8e938981e6c4a302e83ec5beb4630147c7311183cf61069af16333d"
+  url "https://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.0-rc3/llvm-project-21.1.0-rc3.src.tar.xz"
+  sha256 "7c61598f3902e61499b4a8d0302087ed2421c75bf504d084f2e6fa5450ab94d7"
   # The LLVM Project is under the Apache License v2.0 with LLVM Exceptions
   license "Apache-2.0" => { with: "LLVM-exception" }
   head "https://github.com/llvm/llvm-project.git", branch: "main"
diff --git a/Formula/l/llvm.rb b/Formula/l/llvm.rb
index 3eadc8f220fbd..1140deb097d00 100644
--- a/Formula/l/llvm.rb
+++ b/Formula/l/llvm.rb
@@ -6,8 +6,8 @@ class Llvm < Formula
   head "https://github.com/llvm/llvm-project.git", branch: "main"
 
   stable do
-    url "https://github.com/llvm/llvm-project/releases/download/llvmorg-20.1.8/llvm-project-20.1.8.src.tar.xz"
-    sha256 "6898f963c8e938981e6c4a302e83ec5beb4630147c7311183cf61069af16333d"
+    url "https://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.0-rc3/llvm-project-21.1.0-rc3.src.tar.xz"
+    sha256 "7c61598f3902e61499b4a8d0302087ed2421c75bf504d084f2e6fa5450ab94d7"
 
     # Fix triple config loading for clang-cl
     # https://github.com/llvm/llvm-project/pull/111397
@@ -64,6 +64,14 @@ def clang_config_file_dir
   end
 
   def install
+    # Work around OOM error on arm64 linux runner by reducing number of jobs
+    github_arm64_linux = OS.linux? && Hardware::CPU.arm? &&
+                         ENV["HOMEBREW_GITHUB_ACTIONS"].present? &&
+                         ENV["GITHUB_ACTIONS_HOMEBREW_SELF_HOSTED"].blank?
+    if github_arm64_linux && (jobs = ENV.make_jobs - 1).positive?
+      ENV["CMAKE_BUILD_PARALLEL_LEVEL"] = ENV["HOMEBREW_MAKE_JOBS"] = jobs.to_s
+    end
+
     # The clang bindings need a little help finding our libclang.
     inreplace "clang/bindings/python/clang/cindex.py",
               /^(\s*library_path\s*=\s*)None$/,
@@ -80,7 +88,6 @@ def install
       libcxx
       libcxxabi
       libunwind
-      pstl
     ]
 
     unless versioned_formula?
@@ -192,6 +199,7 @@ def install
       args << "-DLLVM_BINUTILS_INCDIR=#{Formula["binutils"].opt_include}"
       # Parts of Polly fail to correctly build with PIC when being used for DSOs.
       args << "-DCMAKE_POSITION_INDEPENDENT_CODE=ON"
+
       runtimes_cmake_args += %w[
         -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=OFF
         -DCMAKE_POSITION_INDEPENDENT_CODE=ON
diff --git a/Formula/m/mesa.rb b/Formula/m/mesa.rb
index db84e6708082c..e3a303d877529 100644
--- a/Formula/m/mesa.rb
+++ b/Formula/m/mesa.rb
@@ -20,6 +20,7 @@ class Mesa < Formula
     { "GPL-1.0-or-later" => { with: "Linux-syscall-note" } }, # include/drm-uapi/sync_file.h
     { "GPL-2.0-only" => { with: "Linux-syscall-note" } }, # include/drm-uapi/{d3dkmthk.h,dma-buf.h,etnaviv_drm.h}
   ]
+  revision 1
   head "https://gitlab.freedesktop.org/mesa/mesa.git", branch: "main"
 
   bottle do
@@ -141,6 +142,9 @@ def install
       -Dvideo-codecs=all
     ]
     args += if OS.mac?
+      # Work around .../rusticl_system_bindings.h:1:10: fatal error: 'stdio.h' file not found
+      ENV["SDKROOT"] = MacOS.sdk_for_formula(self).path
+
       %W[
         -Dgallium-drivers=llvmpipe,zink
         -Dmoltenvk-dir=#{Formula["molten-vk"].prefix}
@@ -149,8 +153,13 @@ def install
         -Dvulkan-layers=intel-nullhw,overlay,screenshot,vram-report-limit
       ]
     else
-      %w[
+      # Not all supported drivers are being auto-enabled on x86 Linux.
+      # TODO: Determine the explicit drivers list for ARM Linux.
+      drivers = Hardware::CPU.intel? ? "all" : "auto"
+
+      %W[
         -Degl=enabled
+        -Dgallium-drivers=#{drivers}
         -Dgallium-extra-hud=true
         -Dgallium-va=enabled
         -Dgallium-vdpau=enabled
@@ -164,27 +173,12 @@ def install
         -Dplatforms=x11,wayland
         -Dtools=drm-shim,etnaviv,freedreno,glsl,intel,nir,nouveau,lima,panfrost,asahi,imagination,dlclose-skip
         -Dvalgrind=enabled
+        -Dvulkan-drivers=#{drivers}
         -Dvulkan-layers=device-select,intel-nullhw,overlay,screenshot,vram-report-limit
         --force-fallback-for=indexmap,paste,pest_generator,roxmltree,rustc-hash,syn
       ]
     end
 
-    # Not all supported drivers are being auto-enabled on x86 Linux.
-    # TODO: Determine the explicit drivers list for ARM Linux.
-    if OS.linux?
-      args += if Hardware::CPU.intel?
-        %w[
-          -Dgallium-drivers=all
-          -Dvulkan-drivers=all
-        ]
-      else
-        %w[
-          -Dgallium-drivers=auto
-          -Dvulkan-drivers=auto
-        ]
-      end
-    end
-
     system "meson", "setup", "build", *args, *std_meson_args
     system "meson", "compile", "-C", "build", "--verbose"
     system "meson", "install", "-C", "build"
diff --git a/Formula/n/nvc.rb b/Formula/n/nvc.rb
index e8acb9250ae8b..17039cbb54996 100644
--- a/Formula/n/nvc.rb
+++ b/Formula/n/nvc.rb
@@ -4,6 +4,7 @@ class Nvc < Formula
   url "https://github.com/nickg/nvc/releases/download/r1.17.2/nvc-1.17.2.tar.gz"
   sha256 "f330dc736d579df7ab494ff0853fe8929243c4234f7cc4d1e9df55d2ea41fbfb"
   license "GPL-3.0-or-later"
+  revision 1
 
   bottle do
     sha256 arm64_sequoia: "87e7db44ec8aafac1756149821faae990bcc3e5282e5a59239ba6c93c6dfeeb7"
diff --git a/Formula/r/rust.rb b/Formula/r/rust.rb
index aeb46f81cf691..de9c8b9445606 100644
--- a/Formula/r/rust.rb
+++ b/Formula/r/rust.rb
@@ -2,6 +2,7 @@ class Rust < Formula
   desc "Safe, concurrent, practical language"
   homepage "https://www.rust-lang.org/"
   license any_of: ["Apache-2.0", "MIT"]
+  revision 1
 
   stable do
     url "https://static.rust-lang.org/dist/rustc-1.89.0-src.tar.gz"
diff --git a/Formula/s/spirv-headers.rb b/Formula/s/spirv-headers.rb
index ef395abc6ddde..f85a4d181d444 100644
--- a/Formula/s/spirv-headers.rb
+++ b/Formula/s/spirv-headers.rb
@@ -1,11 +1,21 @@
 class SpirvHeaders < Formula
   desc "Headers for SPIR-V"
   homepage "https://github.com/KhronosGroup/SPIRV-Headers"
-  url "https://github.com/KhronosGroup/SPIRV-Headers/archive/refs/tags/vulkan-sdk-1.4.321.0.tar.gz"
-  sha256 "5bbea925663d4cd2bab23efad53874f2718248a73dcaf9dd21dff8cb48e602fc"
   license "MIT"
+  revision 1
   head "https://github.com/KhronosGroup/SPIRV-Headers.git", branch: "main"
 
+  stable do
+    url "https://github.com/KhronosGroup/SPIRV-Headers/archive/refs/tags/vulkan-sdk-1.4.321.0.tar.gz"
+    sha256 "5bbea925663d4cd2bab23efad53874f2718248a73dcaf9dd21dff8cb48e602fc"
+
+    # Backport SPV_INTEL_function_variants for SPIRV LLVM Translator >= 21
+    patch do
+      url "https://github.com/KhronosGroup/SPIRV-Headers/commit/9e3836d7d6023843a72ecd3fbf3f09b1b6747a9e.patch?full_index=1"
+      sha256 "44eff041125f59dce93272be22226ab5e48fe4cf2397e422692d0c8679f40d51"
+    end
+  end
+
   livecheck do
     url :stable
     regex(/^(?:vulkan[._-])?sdk[._-]v?(\d+(?:\.\d+)+)$/i)
diff --git a/Formula/s/spirv-llvm-translator.rb b/Formula/s/spirv-llvm-translator.rb
index 13a1c266bdeae..1130bdee1c9c2 100644
--- a/Formula/s/spirv-llvm-translator.rb
+++ b/Formula/s/spirv-llvm-translator.rb
@@ -1,8 +1,8 @@
 class SpirvLlvmTranslator < Formula
   desc "Tool and a library for bi-directional translation between SPIR-V and LLVM IR"
   homepage "https://github.com/KhronosGroup/SPIRV-LLVM-Translator"
-  url "https://github.com/KhronosGroup/SPIRV-LLVM-Translator/archive/refs/tags/v20.1.5.tar.gz"
-  sha256 "83048509774d865dab7631c887b0673753f59f337256bb56829ea32f30d7584b"
+  url "https://github.com/KhronosGroup/SPIRV-LLVM-Translator/archive/refs/tags/v21.1.0.tar.gz"
+  sha256 "4f7019a06c731daebbc18080db338964002493ead4cfb440fef95d120c50a170"
   license "Apache-2.0" => { with: "LLVM-exception" }
 
   bottle do
diff --git a/Formula/s/symengine.rb b/Formula/s/symengine.rb
index 5863c681f539c..cf0c06a68e172 100644
--- a/Formula/s/symengine.rb
+++ b/Formula/s/symengine.rb
@@ -4,7 +4,7 @@ class Symengine < Formula
   url "https://github.com/symengine/symengine/archive/refs/tags/v0.14.0.tar.gz"
   sha256 "11c5f64e9eec998152437f288b8429ec001168277d55f3f5f1df78e3cf129707"
   license "MIT"
-  revision 3
+  revision 4
 
   bottle do
     sha256 cellar: :any,                 arm64_sequoia: "b413d0e962039cc33ce647e56b64d1e14e0485e9fb03aa9bb05c2a8815f2c77c"
diff --git a/Formula/w/wasi-runtimes.rb b/Formula/w/wasi-runtimes.rb
index e4f26f1ccf908..3e9eb9e35fff7 100644
--- a/Formula/w/wasi-runtimes.rb
+++ b/Formula/w/wasi-runtimes.rb
@@ -1,8 +1,8 @@
 class WasiRuntimes < Formula
   desc "Compiler-RT and libc++ runtimes for WASI"
   homepage "https://wasi.dev"
-  url "https://github.com/llvm/llvm-project/releases/download/llvmorg-20.1.8/llvm-project-20.1.8.src.tar.xz"
-  sha256 "6898f963c8e938981e6c4a302e83ec5beb4630147c7311183cf61069af16333d"
+  url "https://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.0-rc3/llvm-project-21.1.0-rc3.src.tar.xz"
+  sha256 "7c61598f3902e61499b4a8d0302087ed2421c75bf504d084f2e6fa5450ab94d7"
   license "Apache-2.0" => { with: "LLVM-exception" }
   head "https://github.com/llvm/llvm-project.git", branch: "main"
 
diff --git a/audit_exceptions/unstable_allowlist.json b/audit_exceptions/unstable_allowlist.json
index accf34288e516..e7da5feebeed1 100644
--- a/audit_exceptions/unstable_allowlist.json
+++ b/audit_exceptions/unstable_allowlist.json
@@ -2,13 +2,17 @@
   "aalib": "1.4rc",
   "automysqlbackup": "3.0-rc",
   "aview": "1.3.0rc",
+  "flang": "21.1.0-rc",
   "ftgl": "2.1.3-rc",
   "libcaca": "0.99b",
   "librasterlite2": "1.1.0-beta",
+  "lld": "21.1.0-rc",
+  "llvm": "21.1.0-rc",
   "premake": "5.0.0-beta",
   "pwnat": "0.3-beta",
   "recode": "3.7-beta",
   "spatialite-gui": "2.1.0-beta",
   "tcptraceroute": "1.5beta",
-  "vbindiff": "3.0_beta"
+  "vbindiff": "3.0_beta",
+  "wasi-runtimes": "21.1.0-rc"
 }