diff --git a/MODULE.bazel b/MODULE.bazel
index adabcae3a8c3..177e6859a9c0 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -88,20 +88,19 @@ git_override(
     remote = "https://github.com/hedronvision/bazel-compile-commands-extractor.git",
 )
 
+# Required for llvm-project.
+bazel_dep(name = "platforms", version = "0.0.8")
+bazel_dep(name = "zlib", version = "1.3", repo_name = "llvm_zlib")
+bazel_dep(name = "zstd", version = "1.5.5", repo_name = "llvm_zstd")
+
 ###############################################################################
 # llvm-project
 ###############################################################################
 
 # We pin to specific upstream commits and try to track top-of-tree reasonably
 # closely rather than pinning to a specific release.
-llvm_project_version = "3d51010a3350660160981c6b8e624dcc87c208a3"
-
-# Required for llvm-project.
-bazel_dep(name = "platforms", version = "0.0.8")
-
-# zlib and zstd dependencies are copied from
-bazel_dep(name = "zlib", version = "1.3", repo_name = "llvm_zlib")
-bazel_dep(name = "zstd", version = "1.5.5", repo_name = "llvm_zstd")
+# HEAD as of 2024-01-03.
+llvm_project_version = "82e33d6203f62c0be16f8da8d4178e7fa9e790ea"
 
 # Load a repository for the raw llvm-project, pre-overlay.
 http_archive(
@@ -113,7 +112,7 @@ http_archive(
         "@carbon//bazel/llvm_project:0002_Added_Bazel_build_for_compiler_rt_fuzzer.patch",
         "@carbon//bazel/llvm_project:0003_Add_library_for_clangd.patch",
     ],
-    sha256 = "efbca707a6eb1c714b849de120309070eef282660c0f4be5b68efef62cc95cf5",
+    sha256 = "402a6dc72452f24ff27ae8157c6d55ea74124de83c57855bbff89b85787fad1c",
     strip_prefix = "llvm-project-{0}".format(llvm_project_version),
     urls = ["https://github.com/llvm/llvm-project/archive/{0}.tar.gz".format(llvm_project_version)],
 )
diff --git a/MODULE.bazel.lock b/MODULE.bazel.lock
index e06d8f20a195..d9ff9cf01049 100644
--- a/MODULE.bazel.lock
+++ b/MODULE.bazel.lock
@@ -1,6 +1,6 @@
 {
   "lockFileVersion": 3,
-  "moduleFileHash": "5f71efedda279a9c13889001d008f8d4e66e61a9a386c9f4b5b13d35275a0da3",
+  "moduleFileHash": "1eff193166261836db74ff270f9bc0ef7d800107c1593383d78cd652d685bb6d",
   "flags": {
     "cmdRegistries": [
       "https://bcr.bazel.build/"
@@ -89,17 +89,17 @@
                   "@carbon//bazel/llvm_project:0002_Added_Bazel_build_for_compiler_rt_fuzzer.patch",
                   "@carbon//bazel/llvm_project:0003_Add_library_for_clangd.patch"
                 ],
-                "sha256": "efbca707a6eb1c714b849de120309070eef282660c0f4be5b68efef62cc95cf5",
-                "strip_prefix": "llvm-project-3d51010a3350660160981c6b8e624dcc87c208a3",
+                "sha256": "402a6dc72452f24ff27ae8157c6d55ea74124de83c57855bbff89b85787fad1c",
+                "strip_prefix": "llvm-project-82e33d6203f62c0be16f8da8d4178e7fa9e790ea",
                 "urls": [
-                  "https://github.com/llvm/llvm-project/archive/3d51010a3350660160981c6b8e624dcc87c208a3.tar.gz"
+                  "https://github.com/llvm/llvm-project/archive/82e33d6203f62c0be16f8da8d4178e7fa9e790ea.tar.gz"
                 ],
                 "name": "llvm-raw"
               },
               "devDependency": false,
               "location": {
                 "file": "@@//:MODULE.bazel",
-                "line": 107,
+                "line": 106,
                 "column": 13
               }
             }
@@ -130,7 +130,7 @@
           "usingModule": "<root>",
           "location": {
             "file": "@@//:MODULE.bazel",
-            "line": 122,
+            "line": 121,
             "column": 29
           },
           "imports": {
@@ -147,7 +147,7 @@
           "usingModule": "<root>",
           "location": {
             "file": "@@//:MODULE.bazel",
-            "line": 134,
+            "line": 133,
             "column": 23
           },
           "imports": {
@@ -163,7 +163,7 @@
               "devDependency": false,
               "location": {
                 "file": "@@//:MODULE.bazel",
-                "line": 135,
+                "line": 134,
                 "column": 17
               }
             }
@@ -177,7 +177,7 @@
           "usingModule": "<root>",
           "location": {
             "file": "@@//:MODULE.bazel",
-            "line": 141,
+            "line": 140,
             "column": 20
           },
           "imports": {
@@ -195,7 +195,7 @@
               "devDependency": false,
               "location": {
                 "file": "@@//:MODULE.bazel",
-                "line": 142,
+                "line": 141,
                 "column": 10
               }
             }
@@ -1694,10 +1694,10 @@
                 "@@//bazel/llvm_project:0002_Added_Bazel_build_for_compiler_rt_fuzzer.patch",
                 "@@//bazel/llvm_project:0003_Add_library_for_clangd.patch"
               ],
-              "sha256": "efbca707a6eb1c714b849de120309070eef282660c0f4be5b68efef62cc95cf5",
-              "strip_prefix": "llvm-project-3d51010a3350660160981c6b8e624dcc87c208a3",
+              "sha256": "402a6dc72452f24ff27ae8157c6d55ea74124de83c57855bbff89b85787fad1c",
+              "strip_prefix": "llvm-project-82e33d6203f62c0be16f8da8d4178e7fa9e790ea",
               "urls": [
-                "https://github.com/llvm/llvm-project/archive/3d51010a3350660160981c6b8e624dcc87c208a3.tar.gz"
+                "https://github.com/llvm/llvm-project/archive/82e33d6203f62c0be16f8da8d4178e7fa9e790ea.tar.gz"
               ],
               "name": "_main~_repo_rules~llvm-raw"
             }
diff --git a/testing/file_test/file_test_base_test.cpp b/testing/file_test/file_test_base_test.cpp
index 4f934ccc235e..d6f3d9b40002 100644
--- a/testing/file_test/file_test_base_test.cpp
+++ b/testing/file_test/file_test_base_test.cpp
@@ -135,7 +135,7 @@ class FileTestBaseTest : public FileTestBase {
       -> llvm::SmallVector<LineNumberReplacement> override {
     auto replacements = FileTestBase::GetLineNumberReplacements(filenames);
     auto filename = std::filesystem::path(test_name().str()).filename();
-    if (llvm::StringRef(filename).startswith("file_only_re_")) {
+    if (llvm::StringRef(filename).starts_with("file_only_re_")) {
       replacements.push_back({.has_file = false,
                               .re = std::make_shared<RE2>(R"(line: (\d+))"),
                               .line_formatv = "{0}"});