diff --git a/dist/index.js b/dist/index.js
index 9ac3d0e..a3bcfd3 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -82166,17 +82166,18 @@ var require_versions = __commonJS({
         x64: "x86_64"
       }[arch];
       const host = `${resolvedArch}-${resolvedOs}`;
-      const machIndex = await getJSON({ url: "https://machengine.org/zig/index.json" });
-      const availableVersions = Object.keys(machIndex);
+      const index = version3.includes("mach") ? await getJSON({ url: "https://machengine.org/zig/index.json" }) : await getJSON({ url: "https://ziglang.org/download/index.json" });
+      const availableVersions = Object.keys(index);
       const useVersion = semver2.valid(version3) ? semver2.maxSatisfying(availableVersions.filter((v) => semver2.valid(v)), version3) : null;
-      const meta = machIndex[useVersion || version3] || (await getJSON({ url: "https://ziglang.org/download/index.json" }))[useVersion || version3];
+      const meta = index[useVersion || version3] || (await getJSON({ url: "https://ziglang.org/download/index.json" }))[useVersion || version3];
       if (!meta || !meta[host]) {
         throw new Error(`Could not find version ${useVersion || version3} for platform ${host}`);
       }
       const downloadUrl = meta[host].tarball;
       const fileWithoutFileType = downloadUrl.match(/.*\/(.*)(\.zip|\.tar\..*$)/)[1];
       const variantName = path2.basename(meta[host].tarball).replace(`.${ext}`, "").replace(/\+\S*$/, "");
-      return { downloadUrl, fileWithoutFileType, variantName, version: useVersion || version3 };
+      const versionFromDownloadUrl = variantName.match(/[^-]*-[^-]*-[^-]*-(.*)/)[1];
+      return { downloadUrl, fileWithoutFileType, variantName, version: versionFromDownloadUrl };
     }
     __name(resolveVersion2, "resolveVersion");
     module2.exports = {
diff --git a/index.js b/index.js
index 8e2a113..a77c20e 100644
--- a/index.js
+++ b/index.js
@@ -17,6 +17,12 @@ const TOOL_NAME = 'zig'
 async function downloadZig (arch, platform, version, useCache = true) {
   const ext = extForPlatform(platform)
 
+  // There are three levels of data here:
+  // 1. Local cache - this is literally cache already established with the job
+  //    container, and is a pre-unpacked directory
+  // 2. Runner cache - this is a cache that is outside the job, but still
+  //    on the host that is running jobs
+  // 3. The canonical source
   const {
     downloadUrl,
     fileWithoutFileType,
@@ -26,12 +32,14 @@ async function downloadZig (arch, platform, version, useCache = true) {
     ? resolveCommit(arch, platform, version)
     : await resolveVersion(arch, platform, version)
 
+  // Check L1 and return on hit
   const cachedPath = toolCache.find(TOOL_NAME, useVersion)
   if (cachedPath) {
     actions.info(`using cached zig install (version ${useVersion}): ${cachedPath}`)
     return cachedPath
   }
 
+  // Check L2 and return on hit
   const cacheKey = `${TOOL_NAME}-${variantName}`
   if (useCache) {
     const restorePath = path.join(process.env.RUNNER_TOOL_CACHE, TOOL_NAME, useVersion, arch)
@@ -43,6 +51,7 @@ async function downloadZig (arch, platform, version, useCache = true) {
     }
   }
 
+  // Miss on L1 and on L2. Need to go to canonical source
   actions.info(`no cached version found. downloading zig ${variantName}`)
   const downloadPath = await toolCache.downloadTool(downloadUrl)
   const zigPath = ext === 'zip'
diff --git a/test.js b/test.js
index 16843be..cfb7c8b 100644
--- a/test.js
+++ b/test.js
@@ -52,25 +52,25 @@ async function test () {
     downloadUrl: 'https://pkg.machengine.org/zig/zig-macos-aarch64-0.12.0-dev.2063+804cee3b9.tar.xz',
     fileWithoutFileType: 'zig-macos-aarch64-0.12.0-dev.2063+804cee3b9',
     variantName: 'zig-macos-aarch64-0.12.0-dev.2063',
-    version: '2024.1.0-mach'
+    version: '0.12.0-dev.2063'
   })
   assert.deepEqual(await resolveVersion('x64', 'linux', '2024.3.0-mach'), {
     downloadUrl: 'https://pkg.machengine.org/zig/zig-linux-x86_64-0.12.0-dev.3180+83e578a18.tar.xz',
     fileWithoutFileType: 'zig-linux-x86_64-0.12.0-dev.3180+83e578a18',
     variantName: 'zig-linux-x86_64-0.12.0-dev.3180',
-    version: '2024.3.0-mach'
+    version: '0.12.0-dev.3180'
   })
   assert.deepEqual(await resolveVersion('x64', 'win32', '2024.1.0-mach'), {
     downloadUrl: 'https://pkg.machengine.org/zig/zig-windows-x86_64-0.12.0-dev.2063+804cee3b9.zip',
     fileWithoutFileType: 'zig-windows-x86_64-0.12.0-dev.2063+804cee3b9',
     variantName: 'zig-windows-x86_64-0.12.0-dev.2063',
-    version: '2024.1.0-mach'
+    version: '0.12.0-dev.2063'
   })
   assert.deepEqual(await resolveVersion('arm64', 'darwin', '2024.3.0-mach'), {
     downloadUrl: 'https://pkg.machengine.org/zig/zig-macos-aarch64-0.12.0-dev.3180+83e578a18.tar.xz',
     fileWithoutFileType: 'zig-macos-aarch64-0.12.0-dev.3180+83e578a18',
     variantName: 'zig-macos-aarch64-0.12.0-dev.3180',
-    version: '2024.3.0-mach'
+    version: '0.12.0-dev.3180'
   })
   await assert.doesNotReject(resolveVersion('x64', 'linux', 'mach-latest'))
   await assert.doesNotReject(resolveVersion('x64', 'win32', 'mach-latest'))
@@ -78,6 +78,9 @@ async function test () {
   await assert.doesNotReject(resolveVersion('x64', 'linux', 'master'))
   await assert.doesNotReject(resolveVersion('x64', 'win32', 'master'))
   await assert.doesNotReject(resolveVersion('arm64', 'darwin', 'master'))
+
+  assert.notEqual((await resolveVersion('arm64', 'darwin', 'mach-latest')).version, 'mach-latest')
+  assert.notEqual((await resolveVersion('arm64', 'darwin', 'master')).version, 'master')
 }
 
 test().catch((error) => {
diff --git a/versions.js b/versions.js
index c1d6b0a..9e8c2ce 100644
--- a/versions.js
+++ b/versions.js
@@ -70,8 +70,8 @@ function getJSON (opts) {
   *
   * @returns {string} download URL for the version
   * @returns {string} file without file type (to match the function above)
-  * @returns {string} variant name for the version - should be used as cache key
-  * @returns {string} version name - use for display only
+  * @returns {string} variant name for the version - used as L2 (runner) cache key
+  * @returns {string} version name - used as the L1 (job) cache key
   */
 async function resolveVersion (arch, platform, version) {
   const ext = extForPlatform(platform)
@@ -91,17 +91,21 @@ async function resolveVersion (arch, platform, version) {
 
   const host = `${resolvedArch}-${resolvedOs}`
 
-  // const index = await getJSON({ url: 'https://ziglang.org/download/index.json' })
-  const machIndex = await getJSON({ url: 'https://machengine.org/zig/index.json' })
+  // Mach json is advertised as a superset, but it's not updated on the same
+  // timeframe as the ZSF index.json. So notably, 'master' will be an old version
+  // on machengine.org
+  const index = version.includes('mach')
+    ? await getJSON({ url: 'https://machengine.org/zig/index.json' })
+    : await getJSON({ url: 'https://ziglang.org/download/index.json' })
 
-  const availableVersions = Object.keys(machIndex)
+  const availableVersions = Object.keys(index)
   const useVersion = semver.valid(version)
     ? semver.maxSatisfying(availableVersions.filter((v) => semver.valid(v)), version)
     : null
 
   // The mach index is advertised as a strict superset of the ziglang index,
   // but we will fall back to the the ziglang index just in case
-  const meta = machIndex[useVersion || version] ||
+  const meta = index[useVersion || version] ||
     (await getJSON({ url: 'https://ziglang.org/download/index.json' }))[useVersion || version]
 
   if (!meta || !meta[host]) {
@@ -117,7 +121,9 @@ async function resolveVersion (arch, platform, version) {
   // it. This is important as it is used as the cache key
   const variantName = path.basename(meta[host].tarball).replace(`.${ext}`, '').replace(/\+\S*$/, '')
 
-  return { downloadUrl, fileWithoutFileType, variantName, version: useVersion || version }
+  const versionFromDownloadUrl = variantName.match(/[^-]*-[^-]*-[^-]*-(.*)/)[1]
+
+  return { downloadUrl, fileWithoutFileType, variantName, version: versionFromDownloadUrl }
 }
 
 module.exports = {