diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index 1db77f739c6c..f13ebe946097 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -59,26 +59,19 @@ jobs:
           go get github.com/bazelbuild/bazelisk
           echo "$(go env GOPATH)/bin" >> $GITHUB_PATH
 
-      # Setup to the latest LLVM and Clang release.
-      #
-      # Ideally we would use the pre-installed versions in the image, but the
-      # debian packages for LLVM-15 currently don't work for fastbuild.
-      #
-      # For now, we rely on Homebrew to manage installing a correctly built
-      # toolchain. We also take some care to be as resilient as possible to
-      # issues fetching and installing the toolchain.
-      - name: Install Clang/LLVM using brew
+      # On macOS, use Homebrew to install a recent LLVM and Clang.
+      - name: Setup LLVM and Clang (macOS)
+        if: matrix.os == 'macos-latest'
         env:
           HOMEBREW_NO_INSTALL_CLEANUP: 1
           HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK: 1
-        # Use llvm@14 because llvm (15) has sanitizer issues.
         run: |
           echo '*** Updating brew'
           brew update
           echo '*** Installing LLVM deps'
-          brew install --force-bottle --only-dependencies llvm@14
+          brew install --force-bottle --only-dependencies llvm
           echo '*** Installing LLVM itself'
-          brew install --force-bottle --force --verbose llvm@14
+          brew install --force-bottle --force --verbose llvm
           echo '*** brew info llvm'
           brew info llvm
           echo '*** brew config'
@@ -86,6 +79,16 @@ jobs:
           echo '*** Updating PATH'
           echo "$(brew --prefix llvm)/bin" >> $GITHUB_PATH
 
+      # On Ubuntu, use apt.llvm.org to install a recent LLVM and Clang.
+      - name: Setup LLVM and Clang (Ubuntu)
+        if: matrix.os == 'ubuntu-latest'
+        run: |
+          wget https://apt.llvm.org/llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 15 all
+          rm llvm.sh
+          echo "/usr/lib/llvm-15/bin" >> $GITHUB_PATH
+
       # Print the various tool paths and versions to help in debugging.
       - name: Print tool debugging info
         run: |
@@ -114,10 +117,14 @@ jobs:
 
       # Add our bazel configuration and print basic info to ease debugging.
       - name: Configure Bazel and print info
+        env:
+          # Add a cache version for changes that bazel won't otherwise detect,
+          # like llvm version changes.
+          CACHE_VERSION: 1
         run: |
           cat >user.bazelrc <<EOF
           # Enable remote cache for our CI.
-          build --remote_cache=https://storage.googleapis.com/carbon-builds-github-${{ matrix.os }}
+          build --remote_cache=https://storage.googleapis.com/carbon-builds-github-v${CACHE_VERSION}-${{ matrix.os }}
           build --google_credentials=$HOME/gcp-builds-service-account.json
 
           # General build options.
diff --git a/bazel/cc_toolchains/clang_cc_toolchain_config.bzl b/bazel/cc_toolchains/clang_cc_toolchain_config.bzl
index 8db25228df84..342b5a7f9c57 100644
--- a/bazel/cc_toolchains/clang_cc_toolchain_config.bzl
+++ b/bazel/cc_toolchains/clang_cc_toolchain_config.bzl
@@ -21,6 +21,7 @@ load(
     ":clang_detected_variables.bzl",
     "clang_bindir",
     "clang_version",
+    "clang_version_for_cache",
     "clang_include_dirs_list",
     "clang_resource_dir",
     "llvm_bindir",
@@ -191,6 +192,9 @@ def _impl(ctx):
                             "-D__DATE__=\"redacted\"",
                             "-D__TIMESTAMP__=\"redacted\"",
                             "-D__TIME__=\"redacted\"",
+                            # Pass the clang version as a define so that bazel
+                            # caching is more likely to notice version changes.
+                            "-DCLANG_VERSION_FOR_CACHE=\"%s\"" % clang_version_for_cache,
                         ],
                     ),
                     flag_group(
diff --git a/bazel/cc_toolchains/clang_configuration.bzl b/bazel/cc_toolchains/clang_configuration.bzl
index f20f07cc5120..a2cd75d5154c 100644
--- a/bazel/cc_toolchains/clang_configuration.bzl
+++ b/bazel/cc_toolchains/clang_configuration.bzl
@@ -18,25 +18,34 @@ def _run(repository_ctx, cmd):
     return exec_result
 
 def _clang_version(version_output):
-    """Returns clang's major version number, or None if not found."""
+    """Returns version information, or a (None, "unknown") tuple if not found.
+
+    Returns both the major version number (14) and the full version number for
+    caching.
+    """
+    clang_version = None
+    clang_version_for_cache = "unknown"
+
     version_prefix = "clang version "
     version_start = version_output.find(version_prefix)
     if version_start == -1:
         # No version
-        return None
+        return (clang_version, clang_version_for_cache)
     version_start += len(version_prefix)
 
-    # Find a dot to indicate something like 'clang version 14.0.6'.
+    # Find the newline.
+    version_newline = version_output.find("\n", version_start)
+    if version_newline == -1:
+        return (clang_version, clang_version_for_cache)
+    clang_version_for_cache = version_output[version_start:version_newline]
+
+    # Find a dot to indicate something like 'clang version 14.0.6', and grab the
+    # major version.
     version_dot = version_output.find(".", version_start)
-    if version_dot == -1:
-        return None
+    if version_dot != -1 and version_dot < version_newline:
+        clang_version = int(version_output[version_start:version_dot])
 
-    # Make sure the dot was on the same line as the version.
-    if version_output.find("\n", version_start) < version_dot:
-        return None
-
-    # Return the version as int.
-    return int(version_output[version_start:version_dot])
+    return (clang_version, clang_version_for_cache)
 
 def _detect_system_clang(repository_ctx):
     """Detects whether the system-provided clang can be used.
@@ -59,7 +68,8 @@ def _detect_system_clang(repository_ctx):
     version_output = _run(repository_ctx, [cc_path, "--version"]).stdout
     if "clang" not in version_output:
         fail("Searching for clang or CC (%s), and found (%s), which is not a Clang compiler" % (cc, cc_path))
-    return (cc_path, _clang_version(version_output))
+    clang_version, clang_version_for_cache = _clang_version(version_output)
+    return (cc_path, clang_version, clang_version_for_cache)
 
 def _compute_clang_resource_dir(repository_ctx, clang):
     """Runs the `clang` binary to get its resource dir."""
@@ -152,7 +162,9 @@ def _configure_clang_toolchain_impl(repository_ctx):
     # here as the other LLVM tools may not be symlinked into the PATH even if
     # `clang` is. We also insist on finding the basename of `clang++` as that is
     # important for C vs. C++ compiles.
-    (clang, clang_version) = _detect_system_clang(repository_ctx)
+    (clang, clang_version, clang_version_for_cache) = _detect_system_clang(
+        repository_ctx,
+    )
     clang = clang.realpath.dirname.get_child("clang++")
 
     # Compute the various directories used by Clang.
@@ -190,6 +202,7 @@ def _configure_clang_toolchain_impl(repository_ctx):
             "{LLVM_BINDIR}": str(arpath.dirname),
             "{CLANG_BINDIR}": str(clang.dirname),
             "{CLANG_VERSION}": str(clang_version),
+            "{CLANG_VERSION_FOR_CACHE}": clang_version_for_cache.replace('"', "_").replace("\\", "_"),
             "{CLANG_RESOURCE_DIR}": resource_dir,
             "{CLANG_INCLUDE_DIRS_LIST}": str(
                 [str(path) for path in include_dirs],
diff --git a/bazel/cc_toolchains/clang_detected_variables.tpl.bzl b/bazel/cc_toolchains/clang_detected_variables.tpl.bzl
index 955456a5e99f..372474694cfc 100644
--- a/bazel/cc_toolchains/clang_detected_variables.tpl.bzl
+++ b/bazel/cc_toolchains/clang_detected_variables.tpl.bzl
@@ -11,6 +11,7 @@ This file gets processed by a repository rule, substituting the
 llvm_bindir = "{LLVM_BINDIR}"
 clang_bindir = "{CLANG_BINDIR}"
 clang_version = {CLANG_VERSION}
+clang_version_for_cache = "{CLANG_VERSION_FOR_CACHE}"
 clang_resource_dir = "{CLANG_RESOURCE_DIR}"
 clang_include_dirs_list = {CLANG_INCLUDE_DIRS_LIST}
 sysroot_dir = "{SYSROOT}"