diff --git a/lib/entry-points.js b/lib/entry-points.js
index 62b043f7b..091132b1c 100644
--- a/lib/entry-points.js
+++ b/lib/entry-points.js
@@ -147730,6 +147730,8 @@ async function runInActions(action) {
     const actionState = {
       name: action.name,
       startedAt,
+      platform: process.platform,
+      arch: process.arch,
       logger,
       env,
       actions: actionsEnv
@@ -163635,8 +163637,7 @@ function getCredentials(logger, registrySecrets, registriesCredentials, language
   }
   return out;
 }
-function getProxyPackage() {
-  const platform2 = process.platform === "win32" ? "win64" : process.platform === "darwin" ? "osx64" : "linux64";
+function getProxyPackage(platform2) {
   return `${UPDATEJOB_PROXY}-${platform2}.tar.gz`;
 }
 function getFallbackUrl(proxyPackage) {
@@ -163653,20 +163654,27 @@ async function getCliVersionFromFeatures(features) {
   const gitHubVersion = await getGitHubVersion();
   return await features.getEnabledDefaultCliVersions(gitHubVersion.type);
 }
-async function getDownloadUrl(logger, features) {
-  const proxyPackage = getProxyPackage();
+async function getDownloadUrl(action) {
+  let platform2 = getBundlePlatform(action.platform, action.arch);
+  if (platform2 === void 0) {
+    action.logger.warning(
+      `Unsupported platform ${action.platform} on architecture ${action.arch}, defaulting to ${"linux64" /* Linux64 */}`
+    );
+    platform2 = "linux64" /* Linux64 */;
+  }
+  const proxyPackage = getProxyPackage(platform2);
   try {
-    const useFeaturesToDetermineCLI = await features.getValue(
+    const useFeaturesToDetermineCLI = await action.features.getValue(
       "start_proxy_use_features_release" /* StartProxyUseFeaturesRelease */
     );
-    const versionInfo = useFeaturesToDetermineCLI ? (await getCliVersionFromFeatures(features)).enabledVersions[0] : {
+    const versionInfo = useFeaturesToDetermineCLI ? (await getCliVersionFromFeatures(action.features)).enabledVersions[0] : {
       cliVersion,
       tagName: bundleVersion
     };
     const cliRelease = await getReleaseByVersion(versionInfo.tagName);
     for (const asset of cliRelease.data.assets) {
       if (asset.name === proxyPackage) {
-        logger.info(
+        action.logger.info(
           `Found '${proxyPackage}' in release '${versionInfo.tagName}' at '${asset.url}'`
         );
         return {
@@ -163679,11 +163687,11 @@ async function getDownloadUrl(logger, features) {
       }
     }
   } catch (ex) {
-    logger.warning(
+    action.logger.warning(
       `Failed to retrieve information about the linked release: ${getErrorMessage(ex)}`
     );
   }
-  logger.info(
+  action.logger.info(
     `Did not find '${proxyPackage}' in the linked release, falling back to hard-coded version.`
   );
   return {
@@ -163732,9 +163740,10 @@ async function cacheProxy(logger, source, filename, version) {
 function getProxyFilename() {
   return process.platform === "win32" ? `${UPDATEJOB_PROXY}.exe` : UPDATEJOB_PROXY;
 }
-async function getProxyBinaryPath(logger, features) {
+async function getProxyBinaryPath(action) {
+  const logger = action.logger;
   const proxyFileName = getProxyFilename();
-  const proxyInfo = await getDownloadUrl(logger, features);
+  const proxyInfo = await getDownloadUrl(action);
   let proxyBin = toolcache4.find(proxyFileName, proxyInfo.version);
   if (!proxyBin) {
     const apiDetails = getApiDetails();
@@ -164114,7 +164123,7 @@ async function run7(action) {
       all_credentials: credentials,
       ca
     };
-    const proxyBin = await getProxyBinaryPath(logger, features);
+    const proxyBin = await getProxyBinaryPath({ ...action, features });
     const proxyInfo = await startProxy(
       proxyBin,
       proxyConfig,
diff --git a/src/action-common.ts b/src/action-common.ts
index 95323e7f2..17d4344cc 100644
--- a/src/action-common.ts
+++ b/src/action-common.ts
@@ -19,6 +19,10 @@ export interface BaseState {
   name: ActionName;
   /** When the Action was started. */
   startedAt: Date;
+  /** The platform the Action is running on. */
+  platform: NodeJS.Platform;
+  /** The architecture of the host. */
+  arch: NodeJS.Architecture;
 }
 
 /** Describes different state features that an Action may have. */
@@ -98,6 +102,8 @@ export async function runInActions(action: Action) {
     const actionState = {
       name: action.name,
       startedAt,
+      platform: process.platform,
+      arch: process.arch,
       logger,
       env,
       actions: actionsEnv,
diff --git a/src/start-proxy-action.ts b/src/start-proxy-action.ts
index e8b89732f..d965a2dd6 100644
--- a/src/start-proxy-action.ts
+++ b/src/start-proxy-action.ts
@@ -98,7 +98,7 @@ async function run(action: ActionState<["Base", "Logger", "Env", "Actions"]>) {
     };
 
     // Start the Proxy
-    const proxyBin = await getProxyBinaryPath(logger, features);
+    const proxyBin = await getProxyBinaryPath({ ...action, features });
     const proxyInfo = await startProxy(
       proxyBin,
       proxyConfig,
diff --git a/src/start-proxy.test.ts b/src/start-proxy.test.ts
index ee953798b..bd2489713 100644
--- a/src/start-proxy.test.ts
+++ b/src/start-proxy.test.ts
@@ -5,6 +5,7 @@ import * as toolcache from "@actions/tool-cache";
 import test, { ExecutionContext } from "ava";
 import sinon from "sinon";
 
+import { ActionState } from "./action-common";
 import * as apiClient from "./api-client";
 import * as defaults from "./defaults.json";
 import { setUpFeatureFlagTests } from "./feature-flags/testing-util";
@@ -12,12 +13,14 @@ import { UnvalidatedObject, validateSchema } from "./json";
 import { makeFromSchema } from "./json/testing-util";
 import { BuiltInLanguage } from "./languages";
 import { getRunnerLogger, Logger } from "./logging";
+import { BundlePlatform, getBundlePlatform } from "./platform";
 import * as startProxyExports from "./start-proxy";
 import * as statusReport from "./status-report";
 import {
   assertNotLogged,
   checkExpectedLogMessages,
   createFeatures,
+  initAllState,
   makeMacro,
   makeTestToken,
   RecordingLogger,
@@ -685,6 +688,12 @@ test("getCredentials always returns ALWAYS_ENABLED_REGISTRY_TYPE credentials for
   }
 });
 
+test("getProxyPackage - includes platform in name", (t) => {
+  for (const platform of Object.values(BundlePlatform)) {
+    t.true(startProxyExports.getProxyPackage(platform).includes(platform));
+  }
+});
+
 function mockGetApiClient(endpoints: any) {
   return (
     sinon
@@ -721,6 +730,44 @@ function mockOfflineFeatures(tempDir: string, logger: Logger) {
   return setUpFeatureFlagTests(tempDir, logger, gitHubVersion);
 }
 
+/** Gets the `BundlePlatform` based on the `action` state, but defaults to `Linux64` if undefined. */
+function getTestPlatform(action: ActionState<["Base"]>) {
+  return (
+    getBundlePlatform(action.platform, action.arch) ?? BundlePlatform.Linux64
+  );
+}
+
+test.serial(
+  "getDownloadUrl logs unknown platforms/arch and defaults to linux64",
+  async (t) => {
+    const logger = new RecordingLogger();
+    mockGetReleaseByTag();
+
+    await withTmpDir(async (tempDir) => {
+      const features = mockOfflineFeatures(tempDir, logger);
+      const state = initAllState({
+        platform: "android",
+        arch: "ppc",
+        logger,
+        features,
+      });
+      const info = await startProxyExports.getDownloadUrl(state);
+
+      t.is(info.version, startProxyExports.UPDATEJOB_PROXY_VERSION);
+      t.is(
+        info.url,
+        startProxyExports.getFallbackUrl(
+          startProxyExports.getProxyPackage(BundlePlatform.Linux64),
+        ),
+      );
+
+      t.true(
+        logger.hasMessage(`Unsupported platform android on architecture ppc`),
+      );
+    });
+  },
+);
+
 test.serial(
   "getDownloadUrl returns fallback when `getReleaseByVersion` rejects",
   async (t) => {
@@ -729,15 +776,15 @@ test.serial(
 
     await withTmpDir(async (tempDir) => {
       const features = mockOfflineFeatures(tempDir, logger);
-      const info = await startProxyExports.getDownloadUrl(
-        getRunnerLogger(true),
-        features,
-      );
+      const state = initAllState({ logger, features });
+      const info = await startProxyExports.getDownloadUrl(state);
 
       t.is(info.version, startProxyExports.UPDATEJOB_PROXY_VERSION);
       t.is(
         info.url,
-        startProxyExports.getFallbackUrl(startProxyExports.getProxyPackage()),
+        startProxyExports.getFallbackUrl(
+          startProxyExports.getProxyPackage(getTestPlatform(state)),
+        ),
       );
     });
   },
@@ -751,18 +798,18 @@ test.serial(
 
     await withTmpDir(async (tempDir) => {
       const features = mockOfflineFeatures(tempDir, logger);
+      const state = initAllState({ logger, features });
 
       for (const assets of testAssets) {
         const stub = mockGetReleaseByTag(assets);
-        const info = await startProxyExports.getDownloadUrl(
-          getRunnerLogger(true),
-          features,
-        );
+        const info = await startProxyExports.getDownloadUrl(state);
 
         t.is(info.version, startProxyExports.UPDATEJOB_PROXY_VERSION);
         t.is(
           info.url,
-          startProxyExports.getFallbackUrl(startProxyExports.getProxyPackage()),
+          startProxyExports.getFallbackUrl(
+            startProxyExports.getProxyPackage(getTestPlatform(state)),
+          ),
         );
 
         stub.restore();
@@ -773,18 +820,19 @@ test.serial(
 
 test.serial("getDownloadUrl returns matching release asset", async (t) => {
   const logger = new RecordingLogger();
+  const state = initAllState({ logger });
   const assets = [
     { name: "foo", url: "other-url" },
-    { name: startProxyExports.getProxyPackage(), url: "url-we-want" },
+    {
+      name: startProxyExports.getProxyPackage(getTestPlatform(state)),
+      url: "url-we-want",
+    },
   ];
   mockGetReleaseByTag(assets);
 
   await withTmpDir(async (tempDir) => {
     const features = mockOfflineFeatures(tempDir, logger);
-    const info = await startProxyExports.getDownloadUrl(
-      getRunnerLogger(true),
-      features,
-    );
+    const info = await startProxyExports.getDownloadUrl({ ...state, features });
 
     t.is(info.version, defaults.cliVersion);
     t.is(info.url, "url-we-want");
@@ -918,7 +966,9 @@ test.serial(
       sinon.stub(toolcache, "find").returns(toolcachePath);
 
       const features = mockOfflineFeatures(tempDir, logger);
-      const path = await startProxyExports.getProxyBinaryPath(logger, features);
+      const path = await startProxyExports.getProxyBinaryPath(
+        initAllState({ logger, features }),
+      );
 
       t.assert(path);
       t.is(
@@ -933,9 +983,13 @@ test.serial(
   "getProxyBinaryPath - downloads proxy if not in cache",
   async (t) => {
     const logger = new RecordingLogger();
+    const state = initAllState({ logger });
     const downloadUrl = "url-we-want";
     mockGetReleaseByTag([
-      { name: startProxyExports.getProxyPackage(), url: downloadUrl },
+      {
+        name: startProxyExports.getProxyPackage(getTestPlatform(state)),
+        url: downloadUrl,
+      },
     ]);
 
     const toolcachePath = "/path/to/proxy/dir";
@@ -958,10 +1012,10 @@ test.serial(
       .resolves(extractedPath);
     const cacheDir = sinon.stub(toolcache, "cacheDir").resolves(toolcachePath);
 
-    const path = await startProxyExports.getProxyBinaryPath(
-      logger,
-      createFeatures([]),
-    );
+    const path = await startProxyExports.getProxyBinaryPath({
+      ...state,
+      features: createFeatures([]),
+    });
 
     t.assert(find.calledOnce);
     t.assert(getApiDetails.calledOnce);
@@ -976,7 +1030,7 @@ test.serial(
     );
 
     checkExpectedLogMessages(t, logger.messages, [
-      `Found '${startProxyExports.getProxyPackage()}' in release '${defaults.bundleVersion}' at '${downloadUrl}'`,
+      `Found '${startProxyExports.getProxyPackage(getTestPlatform(state))}' in release '${defaults.bundleVersion}' at '${downloadUrl}'`,
     ]);
   },
 );
@@ -985,6 +1039,7 @@ test.serial(
   "getProxyBinaryPath - downloads proxy based on features if not in cache",
   async (t) => {
     const logger = new RecordingLogger();
+    const state = initAllState({ logger });
     const expectedTag = "codeql-bundle-v2.20.1";
     const expectedParams = {
       owner: "github",
@@ -994,7 +1049,7 @@ test.serial(
     const downloadUrl = "url-we-want";
     const assets = [
       {
-        name: startProxyExports.getProxyPackage(),
+        name: startProxyExports.getProxyPackage(getTestPlatform(state)),
         url: downloadUrl,
       },
     ];
@@ -1045,7 +1100,10 @@ test.serial(
         .resolves({
           enabledVersions: [{ cliVersion: "2.20.1", tagName: expectedTag }],
         });
-      const path = await startProxyExports.getProxyBinaryPath(logger, features);
+      const path = await startProxyExports.getProxyBinaryPath({
+        ...state,
+        features,
+      });
 
       t.assert(getDefaultCliVersion.calledOnce);
       sinon.assert.calledOnceWithMatch(
@@ -1067,7 +1125,7 @@ test.serial(
     });
 
     checkExpectedLogMessages(t, logger.messages, [
-      `Found '${startProxyExports.getProxyPackage()}' in release '${expectedTag}' at '${downloadUrl}'`,
+      `Found '${startProxyExports.getProxyPackage(getTestPlatform(state))}' in release '${expectedTag}' at '${downloadUrl}'`,
     ]);
   },
 );
diff --git a/src/start-proxy.ts b/src/start-proxy.ts
index caa1b3054..6221c9940 100644
--- a/src/start-proxy.ts
+++ b/src/start-proxy.ts
@@ -3,6 +3,7 @@ import * as path from "path";
 import * as core from "@actions/core";
 import * as toolcache from "@actions/tool-cache";
 
+import { ActionState } from "./action-common";
 import {
   getApiClient,
   getApiDetails,
@@ -20,6 +21,7 @@ import {
 import * as json from "./json";
 import { BuiltInLanguage } from "./languages";
 import { Logger } from "./logging";
+import { BundlePlatform, getBundlePlatform } from "./platform";
 import {
   Address,
   Registry,
@@ -370,14 +372,10 @@ export function getCredentials(
 
 /**
  * Gets the name of the proxy release asset for the current platform.
+ *
+ * @param platform The platform to get the asset name for.
  */
-export function getProxyPackage(): string {
-  const platform =
-    process.platform === "win32"
-      ? "win64"
-      : process.platform === "darwin"
-        ? "osx64"
-        : "linux64";
+export function getProxyPackage(platform: BundlePlatform): string {
   return `${UPDATEJOB_PROXY}-${platform}.tar.gz`;
 }
 
@@ -417,25 +415,33 @@ async function getCliVersionFromFeatures(
  * Determines the URL of the proxy release asset that we should download if its not
  * already in the toolcache, and its version.
  *
- * @param logger The logger to use.
- * @param features Information about enabled features.
+ * @param action The action state.
  * @returns Returns the download URL and version of the proxy package we plan to use.
  */
 export async function getDownloadUrl(
-  logger: Logger,
-  features: FeatureEnablement,
+  action: ActionState<["Base", "Logger", "FeatureFlags"]>,
 ): Promise<{ url: string; version: string }> {
-  const proxyPackage = getProxyPackage();
+  // Default to linux64 if we don't recognise the platform+arch pair.
+  // This maintains the behaviour we had before switching to `getBundlePlatform` here.
+  let platform = getBundlePlatform(action.platform, action.arch);
+  if (platform === undefined) {
+    action.logger.warning(
+      `Unsupported platform ${action.platform} on architecture ${action.arch}, defaulting to ${BundlePlatform.Linux64}`,
+    );
+    platform = BundlePlatform.Linux64;
+  }
+
+  const proxyPackage = getProxyPackage(platform);
 
   try {
-    const useFeaturesToDetermineCLI = await features.getValue(
+    const useFeaturesToDetermineCLI = await action.features.getValue(
       Feature.StartProxyUseFeaturesRelease,
     );
 
     // Retrieve information about the CLI version we should use. This will be either the linked
     // version, or the one enabled by FFs.
     const versionInfo = useFeaturesToDetermineCLI
-      ? (await getCliVersionFromFeatures(features)).enabledVersions[0]
+      ? (await getCliVersionFromFeatures(action.features)).enabledVersions[0]
       : {
           cliVersion: defaults.cliVersion,
           tagName: defaults.bundleVersion,
@@ -447,7 +453,7 @@ export async function getDownloadUrl(
     // Search the release's assets to find the one we are looking for.
     for (const asset of cliRelease.data.assets) {
       if (asset.name === proxyPackage) {
-        logger.info(
+        action.logger.info(
           `Found '${proxyPackage}' in release '${versionInfo.tagName}' at '${asset.url}'`,
         );
         return {
@@ -460,13 +466,13 @@ export async function getDownloadUrl(
       }
     }
   } catch (ex) {
-    logger.warning(
+    action.logger.warning(
       `Failed to retrieve information about the linked release: ${getErrorMessage(ex)}`,
     );
   }
 
   // Fallback to the hard-coded URL.
-  logger.info(
+  action.logger.info(
     `Did not find '${proxyPackage}' in the linked release, falling back to hard-coded version.`,
   );
   return {
@@ -559,15 +565,15 @@ export function getProxyFilename() {
  * runner's tool cache. Otherwise, it downloads and extracts the proxy binary,
  * and stores it in the tool cache.
  *
- * @param logger The logger to use.
+ * @param action The action state.
  * @returns The path to the proxy binary.
  */
 export async function getProxyBinaryPath(
-  logger: Logger,
-  features: FeatureEnablement,
+  action: ActionState<["Base", "Logger", "FeatureFlags"]>,
 ): Promise<string> {
+  const logger = action.logger;
   const proxyFileName = getProxyFilename();
-  const proxyInfo = await getDownloadUrl(logger, features);
+  const proxyInfo = await getDownloadUrl(action);
 
   let proxyBin = toolcache.find(proxyFileName, proxyInfo.version);
   if (!proxyBin) {
diff --git a/src/testing-utils.ts b/src/testing-utils.ts
index f15cee2e7..a5ba50554 100644
--- a/src/testing-utils.ts
+++ b/src/testing-utils.ts
@@ -234,6 +234,8 @@ export function initAllState(
   return {
     name: ActionName.Init,
     startedAt: new Date(),
+    platform: process.platform,
+    arch: process.arch,
     logger: new RecordingLogger(),
     env,
     actions: getTestActionsEnv(env),