diff --git a/apps/server/src/provider/Drivers/AntigravityDriver.test.ts b/apps/server/src/provider/Drivers/AntigravityDriver.test.ts
index 922a27df5768..33e3faa2f74a 100644
--- a/apps/server/src/provider/Drivers/AntigravityDriver.test.ts
+++ b/apps/server/src/provider/Drivers/AntigravityDriver.test.ts
@@ -58,7 +58,7 @@ function shellQuote(value: string): string {
 }
 
 const makeHarness = Effect.fn("makeAntigravityDriverHarness")(function* (
-  options: { readonly config?: Partial<AntigravitySettings> } = {},
+  options: { readonly config?: Partial<AntigravitySettings>; readonly enabled?: boolean } = {},
 ) {
   const fs = yield* FileSystem.FileSystem;
   const path = yield* Path.Path;
@@ -129,6 +129,16 @@ const makeHarness = Effect.fn("makeAntigravityDriverHarness")(function* (
 
   const installation = Layer.mock(AntigravityInstallation)({
     managedDirectory: root,
+    resolve: (binaryPath, environment) =>
+      Effect.gen(function* () {
+        if (controls.failResolution) {
+          return yield* new AntigravityInstallationError({
+            operation: "resolve",
+            detail: "Fixture resolution failed.",
+          });
+        }
+        return controls.selected;
+      }),
     acquire: (binaryPath, environment) =>
       Effect.gen(function* () {
         acquisitions.push({ binaryPath, path: environment?.PATH });
@@ -174,7 +184,7 @@ const makeHarness = Effect.fn("makeAntigravityDriverHarness")(function* (
   const instance = yield* AntigravityDriver.create({
     instanceId,
     displayName: "Google test account",
-    enabled: false,
+    enabled: options.enabled ?? false,
     config: { ...AntigravityDriver.defaultConfig(), ...options.config },
     environment: [
       { name: "PATH", value: instancePath },
@@ -435,4 +445,15 @@ it.layer(testLayer)("AntigravityDriver", (it) => {
       yield* h.assertClosed;
     }).pipe(Effect.scoped),
   );
+
+  it.effect("probes through installation resolution without launching a process", () =>
+    Effect.gen(function* () {
+      const h = yield* makeHarness({ enabled: true });
+      const snapshot = yield* h.instance.snapshot.refresh;
+      expect(snapshot.installed).toBe(true);
+      expect(snapshot.version).toBe(h.first.version);
+      expect(h.launches).toEqual([]);
+      expect(h.acquisitions).toEqual([]);
+    }).pipe(Effect.scoped),
+  );
 });
diff --git a/apps/server/src/provider/Drivers/AntigravityDriver.ts b/apps/server/src/provider/Drivers/AntigravityDriver.ts
index 0082f3cbdc30..021582aef6fe 100644
--- a/apps/server/src/provider/Drivers/AntigravityDriver.ts
+++ b/apps/server/src/provider/Drivers/AntigravityDriver.ts
@@ -38,7 +38,10 @@ import {
 } from "../acp/AntigravityAcpSupport.ts";
 import type { AcpSessionRuntime, AcpSessionRuntimeStartResult } from "../acp/AcpSessionRuntime.ts";
 import type { ServerProviderDraft } from "../providerSnapshot.ts";
-import { removeAntigravitySessionFiles } from "../acp/AntigravitySessionFiles.ts";
+import {
+  cleanOrphanedAntigravityTempDirs,
+  removeAntigravitySessionFiles,
+} from "../acp/AntigravitySessionFiles.ts";
 import { ProviderDriverError } from "../Errors.ts";
 import { makeAntigravityAdapter } from "../Layers/AntigravityAdapter.ts";
 import { makeAntigravityProvider } from "../Layers/AntigravityProvider.ts";
@@ -98,6 +101,11 @@ export const AntigravityDriver: ProviderDriver<AntigravitySettings, AntigravityD
         serverConfig.stateDir,
         instanceId,
       );
+      yield* cleanOrphanedAntigravityTempDirs(profileDirectory).pipe(
+        Effect.provideService(FileSystem.FileSystem, fileSystem),
+        Effect.provideService(Path.Path, path),
+        Effect.ignore,
+      );
       const continuationIdentity = defaultProviderContinuationIdentity({
         driverKind: DRIVER,
         instanceId,
@@ -258,24 +266,47 @@ export const AntigravityDriver: ProviderDriver<AntigravitySettings, AntigravityD
       // Kick the TTL-gated manifest refresh alongside the health check, as
       // Codex and Claude do. Without it an environment that only runs
       // Antigravity would keep classifying against a stale disk cache.
+      // Antigravity's binary is a PyInstaller single-file bundle. Spawning it
+      // extracts ~860 MB of files to a temporary directory on every run.
+      // The health probe only needs to verify that the executable and harness
+      // exist on disk and resolve the installed version; actual ACP sessions
+      // and explicit model refreshes spawn the runtime when needed.
       const probe = Effect.gen(function* () {
         yield* modelManifest.refreshInBackground;
-        const processScope = yield* Scope.make();
-        yield* Effect.addFinalizer((exit) => Scope.close(processScope, exit));
-        return yield* authFlow
-          .withProcess(
-            Scope.close(processScope, Exit.void),
-            Effect.gen(function* () {
-              const runtime = yield* makeRuntime({
-                cwd: serverConfig.stateDir,
-                clientInfo: { name: "t3-code-provider-probe", version: "0.0.0" },
-                mcpServers: [],
-              });
-              return yield* runtime.initialize();
-            }),
-          )
-          .pipe(Effect.provideService(Scope.Scope, processScope));
-      }).pipe(Effect.scoped);
+        if (authConfigIssue !== null) {
+          return yield* new ProviderSetupError({
+            instanceId,
+            operation: "configure",
+            detail: authConfigIssue,
+          });
+        }
+        const executable = yield* installation
+          .resolve(settings.binaryPath, processEnvironment)
+          .pipe(
+            Effect.mapError(
+              (cause) =>
+                new ProviderSetupError({
+                  instanceId,
+                  operation: "resolve",
+                  detail: cause.detail,
+                }),
+            ),
+          );
+        return {
+          protocolVersion: 1,
+          agentCapabilities: {
+            loadSession: true,
+            promptCapabilities: { image: true, audio: true, embeddedContext: true },
+            sessionCapabilities: { list: {}, resume: {} },
+          },
+          authMethods: [{ id: "oauth-personal", name: "Log in with Google" }],
+          agentInfo: {
+            name: "antigravity-acp",
+            title: "Google Antigravity",
+            version: executable.version ?? "unknown",
+          },
+        };
+      });
 
       const provider = yield* makeAntigravityProvider(settings, {
         stampIdentity: classifyModels,
diff --git a/apps/server/src/provider/acp/AntigravitySessionFiles.ts b/apps/server/src/provider/acp/AntigravitySessionFiles.ts
index b00bffbc1646..0ba486cdc470 100644
--- a/apps/server/src/provider/acp/AntigravitySessionFiles.ts
+++ b/apps/server/src/provider/acp/AntigravitySessionFiles.ts
@@ -38,6 +38,68 @@ export const removeAntigravitySessionFiles = Effect.fn("removeAntigravitySession
       recursive: true,
       force: true,
     });
+
+    // Best-effort cleanup of any unlocked temporary unpack directories left by PyInstaller
+    const tmpDirectory = path.join(acpDirectory, "tmp");
+    if (yield* fs.exists(tmpDirectory)) {
+      const entries = yield* fs.readDirectory(tmpDirectory).pipe(Effect.orElseSucceed(() => []));
+      for (const entry of entries) {
+        if (entry.startsWith("_MEI")) {
+          yield* fs
+            .remove(path.join(tmpDirectory, entry), { recursive: true, force: true })
+            .pipe(Effect.ignore);
+        }
+      }
+    }
   },
   Effect.catch(() => Effect.logWarning("Could not remove temporary Antigravity session files.")),
 );
+
+/** Sweeps orphaned PyInstaller unpack directories from prior runs. */
+export const cleanOrphanedAntigravityTempDirs = Effect.fn("cleanOrphanedAntigravityTempDirs")(
+  function* (profileDirectory?: string) {
+    const fs = yield* FileSystem.FileSystem;
+    const path = yield* Path.Path;
+
+    // 1. Clean profile-isolated tmp directory if provided
+    if (profileDirectory) {
+      const acpTmp = path.join(profileDirectory, "antigravity-acp", "tmp");
+      if (yield* fs.exists(acpTmp)) {
+        const entries = yield* fs.readDirectory(acpTmp).pipe(Effect.orElseSucceed(() => []));
+        for (const entry of entries) {
+          if (entry.startsWith("_MEI")) {
+            yield* fs
+              .remove(path.join(acpTmp, entry), { recursive: true, force: true })
+              .pipe(Effect.ignore);
+          }
+        }
+      }
+    }
+
+    // 2. Clean orphaned _MEI folders in system temp directory left by previous Antigravity probes on Windows
+    // On Unix, concurrent processes can have their files deleted without file locking protection,
+    // so system temp sweeping is restricted to Windows where active files are lock-protected.
+    if (process.platform === "win32") {
+      const systemTemp = process.env.TEMP || process.env.TMP;
+      if (systemTemp && (yield* fs.exists(systemTemp))) {
+        const entries = yield* fs.readDirectory(systemTemp).pipe(Effect.orElseSucceed(() => []));
+        for (const entry of entries) {
+          if (entry.startsWith("_MEI")) {
+            const fullPath = path.join(systemTemp, entry);
+            const hasGoogle3 = yield* fs
+              .exists(path.join(fullPath, "google3"))
+              .pipe(Effect.orElseSucceed(() => false));
+            const hasGoogle =
+              hasGoogle3 ||
+              (yield* fs
+                .exists(path.join(fullPath, "google"))
+                .pipe(Effect.orElseSucceed(() => false)));
+            if (hasGoogle) {
+              yield* fs.remove(fullPath, { recursive: true, force: true }).pipe(Effect.ignore);
+            }
+          }
+        }
+      }
+    }
+  },
+);
diff --git a/apps/server/src/provider/antigravityAuthSupport.test.ts b/apps/server/src/provider/antigravityAuthSupport.test.ts
index 7f065caa4f6a..165dca65f6c5 100644
--- a/apps/server/src/provider/antigravityAuthSupport.test.ts
+++ b/apps/server/src/provider/antigravityAuthSupport.test.ts
@@ -187,6 +187,29 @@ describe("Antigravity process environment", () => {
     ).toBeNull();
   });
 
+  it("isolates TEMP and TMP to the profile directory on Windows", () => {
+    const windowsProfile: AntigravityProfile = {
+      platform: "win32",
+      geminiHome: "C:\\state\\providers\\antigravity\\profile",
+      acpDirectory: "C:\\state\\providers\\antigravity\\profile\\antigravity-acp",
+      tokenPath: "C:\\state\\providers\\antigravity\\profile\\antigravity-acp\\acp_token.json",
+      browserCommand: "managed-browser-helper",
+    };
+    const spawn = buildAntigravityAcpSpawnInput({
+      installation: {
+        executablePath: "C:\\release\\agy_acp_server.exe",
+        harnessPath: "C:\\release\\localharness_external.exe",
+      },
+      profile: windowsProfile,
+      cwd: "C:\\project",
+      baseEnv: { PATH: "C:\\Windows\\system32", TEMP: "C:\\Users\\user\\AppData\\Local\\Temp" },
+    });
+    expect(spawn.env?.TEMP).toBe(
+      "C:\\state\\providers\\antigravity\\profile\\antigravity-acp\\tmp",
+    );
+    expect(spawn.env?.TMP).toBe("C:\\state\\providers\\antigravity\\profile\\antigravity-acp\\tmp");
+  });
+
   it("uses the registry launch arguments for each supported host platform", () => {
     for (const platform of ["linux", "darwin", "win32"] as const) {
       const spawn = buildAntigravityAcpSpawnInput({
diff --git a/apps/server/src/provider/antigravityAuthSupport.ts b/apps/server/src/provider/antigravityAuthSupport.ts
index 8e0040ae0c3e..acbf2d56596a 100644
--- a/apps/server/src/provider/antigravityAuthSupport.ts
+++ b/apps/server/src/provider/antigravityAuthSupport.ts
@@ -214,6 +214,10 @@ function antigravityEnvironment(
       : auth.authMethod === "agent-platform" && auth.apiKey
         ? { GOOGLE_API_KEY: auth.apiKey }
         : {};
+  const tempDirectory =
+    profile.platform === "win32"
+      ? NodePath.win32.join(profile.acpDirectory, "tmp")
+      : NodePath.join(profile.acpDirectory, "tmp");
   return {
     ...environment,
     ...credential,
@@ -222,6 +226,12 @@ function antigravityEnvironment(
     BROWSER: profile.browserCommand,
     PYTHONUNBUFFERED: "1",
     ELECTRON_RUN_AS_NODE: "1",
+    ...(profile.platform === "win32"
+      ? {
+          TEMP: tempDirectory,
+          TMP: tempDirectory,
+        }
+      : {}),
   };
 }
 
@@ -311,6 +321,7 @@ export const prepareAntigravityProfile = Effect.fn("prepareAntigravityProfile")(
 
   const geminiHome = path.resolve(input.profileDirectory);
   const acpDirectory = path.join(geminiHome, "antigravity-acp");
+  const tempDirectory = path.join(acpDirectory, "tmp");
   const profile: AntigravityProfile = {
     platform,
     geminiHome,
@@ -358,7 +369,7 @@ export const prepareAntigravityProfile = Effect.fn("prepareAntigravityProfile")(
     ),
   );
 
-  for (const directory of [geminiHome, acpDirectory]) {
+  for (const directory of [geminiHome, acpDirectory, tempDirectory]) {
     yield* fs
       .makeDirectory(directory, { recursive: true, mode: 0o700 })
       .pipe(