diff --git a/.gitignore b/.gitignore
index 04f62b9ed..664a85e89 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,6 +17,7 @@ MODULE.bazel.lock
 .DS_Store
 
 # third_party dirs and cache dir checked out by update_deps.py
+/src/third_party/llvm/
 /src/third_party/ndk/
 /src/third_party/ninja/
 /src/third_party/qt/
diff --git a/docs/build_mozc_in_windows.md b/docs/build_mozc_in_windows.md
index abacca0e5..a09795aa1 100644
--- a/docs/build_mozc_in_windows.md
+++ b/docs/build_mozc_in_windows.md
@@ -68,6 +68,7 @@ python build_tools/update_deps.py
 
 In this step, additional build dependencies will be downloaded.
 
+  * [LLVM 19.1.7](https://github.com/llvm/llvm-project/releases/tag/llvmorg-19.1.7)
   * [Ninja 1.11.0](https://github.com/ninja-build/ninja/releases/download/v1.11.0/ninja-win.zip)
   * [Qt 6.8.0](https://download.qt.io/archive/qt/6.8/6.8.0/submodules/qtbase-everywhere-src-6.8.0.tar.xz)
   * [.NET tools](../dotnet-tools.json)
diff --git a/src/build_tools/update_deps.py b/src/build_tools/update_deps.py
index 074216d14..be5b2bb30 100644
--- a/src/build_tools/update_deps.py
+++ b/src/build_tools/update_deps.py
@@ -35,6 +35,7 @@
 """
 
 import argparse
+from collections.abc import Iterator
 import dataclasses
 import hashlib
 import os
@@ -42,6 +43,10 @@
 import shutil
 import stat
 import subprocess
+import sys
+import tarfile
+import time
+from typing import Union
 import zipfile
 
 import requests
@@ -109,6 +114,11 @@ def __hash__(self):
     sha256='d0ee3da143211aa447e750085876c9b9d7bcdd637ab5b2c5b41349c617f22f3b',
 )
 
+LLVM_WIN = ArchiveInfo(
+    url='https://github.com/llvm/llvm-project/releases/download/llvmorg-19.1.7/clang+llvm-19.1.7-x86_64-pc-windows-msvc.tar.xz',
+    size=845236708,
+    sha256='b4557b4f012161f56a2f5d9e877ab9635cafd7a08f7affe14829bd60c9d357f0',
+)
 
 def get_sha256(path: pathlib.Path) -> str:
   """Returns SHA-256 hash digest of the specified file.
@@ -182,6 +192,78 @@ def download(archive: ArchiveInfo, dryrun: bool = False) -> None:
     )
 
 
+class StatefulLLVMExtractionFilter:
+  """A stateful extraction filter for PEP 706.
+
+  See https://peps.python.org/pep-0706/ for details.
+  """
+
+  def __enter__(self):
+    self.printer = ProgressPrinter().__enter__()
+    return self
+
+  def __exit__(self, *exc):
+    self.printer.__exit__(exc)
+
+  def __call__(
+      self,
+      member: tarfile.TarInfo,
+      dest_path: Union[str, pathlib.Path],
+  ) -> Union[tarfile.TarInfo, None]:
+    data = tarfile.data_filter(member, dest_path)
+    if data is None:
+      return None
+
+    skipping = True
+    paths = member.name.split('/')
+    if (
+        len(paths) == 3
+        and paths[1] == 'bin'
+        and paths[2] in ['clang-cl.exe', 'llvm-lib.exe', 'lld-link.exe']
+    ):
+      skipping = False
+    elif len(paths) >= 2 and paths[1] in ['include', 'lib']:
+      skipping = False
+    if skipping:
+      self.printer.print_line('skipping   ' + member.name)
+      return None
+    self.printer.print_line('extracting ' + member.name)
+    return member
+
+
+def extract_llvm(dryrun: bool = False) -> None:
+  """Extract LLVM archive.
+
+  Args:
+    dryrun: True if this is a dry-run.
+  """
+  if not is_windows():
+    return
+
+  archive = LLVM_WIN
+  src = CACHE_DIR.joinpath(archive.filename)
+  dest = ABS_THIRD_PARTY_DIR.joinpath('llvm').absolute()
+
+  if dest.exists():
+    if dryrun:
+      print(f"dryrun: shutil.rmtree(r'{dest}')")
+    else:
+      shutil.rmtree(dest)
+
+  if dryrun:
+    print(f'dryrun: Extracting {src} into {dest}')
+  else:
+    dest.mkdir(parents=True)
+    with tarfile.open(src, mode='r|xz') as f:
+      # tarfile.data_filter is available in Python 3.12+.
+      # See https://peps.python.org/pep-0706/ for details.
+      if getattr(tarfile, 'data_filter', None):
+        with StatefulLLVMExtractionFilter() as filter:
+          f.extractall(path=dest, filter=filter)
+      else:
+        f.extractall(path=dest, members=llvm_extract_filter(f))
+
+
 def extract_ninja(dryrun: bool = False) -> None:
   """Extract ninja-win archive.
 
@@ -329,6 +411,7 @@ def main():
   parser.add_argument('--dryrun', action='store_true', default=False)
   parser.add_argument('--noninja', action='store_true', default=False)
   parser.add_argument('--noqt', action='store_true', default=False)
+  parser.add_argument('--nollvm', action='store_true', default=False)
   parser.add_argument('--nowix', action='store_true', default=False)
   parser.add_argument('--nondk', action='store_true', default=False)
   parser.add_argument('--nosubmodules', action='store_true', default=False)
@@ -349,6 +432,8 @@ def main():
       archives.append(NDK_LINUX)
     elif is_mac():
       archives.append(NDK_MAC)
+  if (not args.nollvm) and is_windows():
+    archives.append(LLVM_WIN)
 
   for archive in archives:
     download(archive, args.dryrun)
@@ -356,6 +441,9 @@ def main():
   if args.cache_only:
     return
 
+  if (LLVM_WIN in archives):
+    extract_llvm(args.dryrun)
+
   if (not args.nowix) and is_windows():
     restore_dotnet_tools(args.dryrun)