diff --git a/packages/backend/src/tokens/__tests__/oauthNegativeCache.test.ts b/packages/backend/src/tokens/__tests__/oauthNegativeCache.test.ts
new file mode 100644
index 00000000000..0d57dd92392
--- /dev/null
+++ b/packages/backend/src/tokens/__tests__/oauthNegativeCache.test.ts
@@ -0,0 +1,147 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { MachineTokenVerificationError, MachineTokenVerificationErrorCode } from '../../errors';
+import {
+  isOAuthTokenCachedAsInvalid,
+  makeCachedInvalidOAuthTokenError,
+  maybeCacheOAuthTokenAsInvalid,
+  resetOAuthNegativeCache,
+} from '../oauthNegativeCache';
+
+const TOKEN = 'oat_abc123';
+const ANOTHER_TOKEN = 'oat_xyz789';
+
+function makeTokenInvalidError() {
+  return new MachineTokenVerificationError({
+    message: 'OAuth token not found',
+    code: MachineTokenVerificationErrorCode.TokenInvalid,
+    status: 404,
+  });
+}
+
+function makeOtherError() {
+  return new MachineTokenVerificationError({
+    message: 'Invalid secret key',
+    code: MachineTokenVerificationErrorCode.InvalidSecretKey,
+    status: 401,
+  });
+}
+
+describe('oauthNegativeCache', () => {
+  beforeEach(() => {
+    resetOAuthNegativeCache();
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  describe('isOAuthTokenCachedAsInvalid', () => {
+    it('returns false for a token that has never been cached', () => {
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(false);
+    });
+
+    it('returns true for a token cached as invalid', () => {
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), TOKEN);
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(true);
+    });
+
+    it('returns false for a different token not in the cache', () => {
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), TOKEN);
+      expect(isOAuthTokenCachedAsInvalid(ANOTHER_TOKEN)).toBe(false);
+    });
+
+    it('returns false and evicts the entry after TTL expires', () => {
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), TOKEN);
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(true);
+
+      vi.advanceTimersByTime(30_001);
+
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(false);
+    });
+
+    it('returns true just before TTL expires', () => {
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), TOKEN);
+      vi.advanceTimersByTime(29_999);
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(true);
+    });
+  });
+
+  describe('maybeCacheOAuthTokenAsInvalid', () => {
+    it('caches when error is TokenInvalid', () => {
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), TOKEN);
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(true);
+    });
+
+    it('does not cache when error is a different MachineTokenVerificationError code', () => {
+      maybeCacheOAuthTokenAsInvalid(makeOtherError(), TOKEN);
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(false);
+    });
+
+    it('does not cache when error is not a MachineTokenVerificationError', () => {
+      maybeCacheOAuthTokenAsInvalid(new Error('network failure'), TOKEN);
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(false);
+    });
+
+    it('does not cache when error is null', () => {
+      maybeCacheOAuthTokenAsInvalid(null, TOKEN);
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(false);
+    });
+
+    it('updates the expiry when caching the same token again', () => {
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), TOKEN);
+
+      vi.advanceTimersByTime(20_000);
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), TOKEN);
+
+      vi.advanceTimersByTime(20_000);
+      // 40s total since first cache, but only 20s since re-cache; should still be valid
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(true);
+
+      vi.advanceTimersByTime(10_001);
+      // 30s since re-cache; should now expire
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(false);
+    });
+  });
+
+  describe('makeCachedInvalidOAuthTokenError', () => {
+    it('returns a MachineTokenVerificationError with TokenInvalid code', () => {
+      const err = makeCachedInvalidOAuthTokenError();
+      expect(err).toBeInstanceOf(MachineTokenVerificationError);
+      expect(err.code).toBe(MachineTokenVerificationErrorCode.TokenInvalid);
+    });
+
+    it('returns an error with status 404', () => {
+      const err = makeCachedInvalidOAuthTokenError();
+      expect(err.status).toBe(404);
+    });
+  });
+
+  describe('resetOAuthNegativeCache', () => {
+    it('clears all cached entries', () => {
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), TOKEN);
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), ANOTHER_TOKEN);
+      resetOAuthNegativeCache();
+      expect(isOAuthTokenCachedAsInvalid(TOKEN)).toBe(false);
+      expect(isOAuthTokenCachedAsInvalid(ANOTHER_TOKEN)).toBe(false);
+    });
+  });
+
+  describe('capacity eviction', () => {
+    it('evicts the oldest entry when the cache reaches MAX_ENTRIES (10,000)', () => {
+      // Fill the cache to max capacity
+      for (let i = 0; i < 10_000; i++) {
+        maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), `oat_token_${i}`);
+      }
+
+      expect(isOAuthTokenCachedAsInvalid('oat_token_0')).toBe(true);
+
+      // Adding one more should evict oat_token_0 (the oldest)
+      maybeCacheOAuthTokenAsInvalid(makeTokenInvalidError(), 'oat_overflow');
+
+      expect(isOAuthTokenCachedAsInvalid('oat_token_0')).toBe(false);
+      expect(isOAuthTokenCachedAsInvalid('oat_overflow')).toBe(true);
+    });
+  });
+});
diff --git a/packages/backend/src/tokens/__tests__/request.test.ts b/packages/backend/src/tokens/__tests__/request.test.ts
index e9b5fa6bfda..48b926d3a44 100644
--- a/packages/backend/src/tokens/__tests__/request.test.ts
+++ b/packages/backend/src/tokens/__tests__/request.test.ts
@@ -2,6 +2,7 @@ import { http, HttpResponse } from 'msw';
 import { afterEach, beforeEach, describe, expect, it, test, vi } from 'vitest';
 
 import { MachineTokenVerificationErrorCode, TokenVerificationErrorReason } from '../../errors';
+import { isOAuthTokenCachedAsInvalid, resetOAuthNegativeCache } from '../oauthNegativeCache';
 import {
   mockExpiredJwt,
   mockInvalidSignatureJwt,
@@ -1452,6 +1453,7 @@ describe('tokens.authenticateRequest(options)', () => {
   describe('Machine authentication', () => {
     afterEach(() => {
       vi.clearAllMocks();
+      resetOAuthNegativeCache();
     });
 
     // Test each token type with parameterized tests
@@ -1762,6 +1764,108 @@ describe('tokens.authenticateRequest(options)', () => {
       });
     });
 
+    describe('OAuth negative cache', () => {
+      afterEach(() => {
+        resetOAuthNegativeCache();
+      });
+
+      test('rejects a previously invalid oat_ token from cache without calling BAPI again', async () => {
+        server.use(
+          http.post(mockMachineAuthResponses.oauth_token.endpoint, () => HttpResponse.json({}, { status: 404 })),
+        );
+        const token = 'oat_invalid_garbage_token';
+        await authenticateRequest(
+          mockRequest({ authorization: `Bearer ${token}` }),
+          mockOptions({ acceptsToken: 'any' }),
+        );
+
+        // BAPI now returns 200, but the token should still be rejected from cache
+        server.use(
+          http.post(mockMachineAuthResponses.oauth_token.endpoint, () =>
+            HttpResponse.json(mockVerificationResults.oauth_token),
+          ),
+        );
+        const second = await authenticateRequest(
+          mockRequest({ authorization: `Bearer ${token}` }),
+          mockOptions({ acceptsToken: 'any' }),
+        );
+        expect(second).toBeMachineUnauthenticated({
+          tokenType: 'oauth_token',
+          reason: MachineTokenVerificationErrorCode.TokenInvalid,
+          message: 'OAuth token not found (code=token-invalid, status=404)',
+        });
+      });
+
+      test('does not cache valid oat_ tokens', async () => {
+        server.use(
+          http.post(mockMachineAuthResponses.oauth_token.endpoint, () =>
+            HttpResponse.json(mockVerificationResults.oauth_token),
+          ),
+        );
+        await authenticateRequest(
+          mockRequest({ authorization: `Bearer ${mockTokens.oauth_token}` }),
+          mockOptions({ acceptsToken: 'oauth_token' }),
+        );
+        expect(isOAuthTokenCachedAsInvalid(mockTokens.oauth_token)).toBe(false);
+      });
+
+      test('does not cache oat_ tokens that fail with non-TokenInvalid errors', async () => {
+        // 401 maps to InvalidSecretKey, not TokenInvalid
+        server.use(
+          http.post(mockMachineAuthResponses.oauth_token.endpoint, () => HttpResponse.json({}, { status: 401 })),
+        );
+        const token = 'oat_secret_key_error_token';
+        await authenticateRequest(
+          mockRequest({ authorization: `Bearer ${token}` }),
+          mockOptions({ acceptsToken: 'oauth_token' }),
+        );
+        expect(isOAuthTokenCachedAsInvalid(token)).toBe(false);
+      });
+
+      test('re-verifies token after cache TTL expires', async () => {
+        vi.useFakeTimers();
+        server.use(
+          http.post(mockMachineAuthResponses.oauth_token.endpoint, () => HttpResponse.json({}, { status: 404 })),
+        );
+        const token = 'oat_will_expire_from_cache';
+        await authenticateRequest(
+          mockRequest({ authorization: `Bearer ${token}` }),
+          mockOptions({ acceptsToken: 'oauth_token' }),
+        );
+        expect(isOAuthTokenCachedAsInvalid(token)).toBe(true);
+
+        vi.advanceTimersByTime(30_001);
+        expect(isOAuthTokenCachedAsInvalid(token)).toBe(false);
+        vi.useRealTimers();
+      });
+
+      test('ak_ tokens are not affected by the cache', async () => {
+        server.use(
+          http.post(mockMachineAuthResponses.api_key.endpoint, () =>
+            HttpResponse.json(mockVerificationResults.api_key),
+          ),
+        );
+        const result = await authenticateRequest(
+          mockRequest({ authorization: `Bearer ${mockTokens.api_key}` }),
+          mockOptions({ acceptsToken: 'api_key' }),
+        );
+        expect(result).toBeMachineAuthenticated();
+      });
+
+      test('mt_ tokens are not affected by the cache', async () => {
+        server.use(
+          http.post(mockMachineAuthResponses.m2m_token.endpoint, () =>
+            HttpResponse.json(mockVerificationResults.m2m_token),
+          ),
+        );
+        const result = await authenticateRequest(
+          mockRequest({ authorization: `Bearer ${mockTokens.m2m_token}` }),
+          mockOptions({ acceptsToken: 'm2m_token' }),
+        );
+        expect(result).toBeMachineAuthenticated();
+      });
+    });
+
     describe('Token Location Validation', () => {
       test.each(tokenTypes)('returns unauthenticated state when %s is in cookie instead of header', async tokenType => {
         const mockToken = mockTokens[tokenType];
diff --git a/packages/backend/src/tokens/machine.ts b/packages/backend/src/tokens/machine.ts
index cfc055e96d3..70e67ba8e14 100644
--- a/packages/backend/src/tokens/machine.ts
+++ b/packages/backend/src/tokens/machine.ts
@@ -90,6 +90,10 @@ export function isMachineTokenByPrefix(token: string): boolean {
   return MACHINE_TOKEN_PREFIXES.some(prefix => token.startsWith(prefix));
 }
 
+export function isOAuthTokenByPrefix(token: string): boolean {
+  return token.startsWith(OAUTH_TOKEN_PREFIX);
+}
+
 /**
  * Checks if a token is a machine token by looking at its prefix or if it's an OAuth/M2M JWT.
  *
diff --git a/packages/backend/src/tokens/oauthNegativeCache.ts b/packages/backend/src/tokens/oauthNegativeCache.ts
new file mode 100644
index 00000000000..b986c0b547c
--- /dev/null
+++ b/packages/backend/src/tokens/oauthNegativeCache.ts
@@ -0,0 +1,44 @@
+import { MachineTokenVerificationError, MachineTokenVerificationErrorCode } from '../errors';
+
+const TTL_MS = 30_000;
+const MAX_ENTRIES = 10_000;
+
+type Entry = { expiresAt: number };
+const cache = new Map<string, Entry>();
+
+export function isOAuthTokenCachedAsInvalid(token: string): boolean {
+  const entry = cache.get(token);
+  if (!entry) {
+    return false;
+  }
+  if (Date.now() >= entry.expiresAt) {
+    cache.delete(token);
+    return false;
+  }
+  return true;
+}
+
+export function maybeCacheOAuthTokenAsInvalid(err: unknown, token: string): void {
+  if (!(err instanceof MachineTokenVerificationError) || err.code !== MachineTokenVerificationErrorCode.TokenInvalid) {
+    return;
+  }
+  if (cache.size >= MAX_ENTRIES) {
+    const oldest = cache.keys().next().value;
+    if (oldest !== undefined) {
+      cache.delete(oldest);
+    }
+  }
+  cache.set(token, { expiresAt: Date.now() + TTL_MS });
+}
+
+export function makeCachedInvalidOAuthTokenError(): MachineTokenVerificationError {
+  return new MachineTokenVerificationError({
+    message: 'OAuth token not found',
+    code: MachineTokenVerificationErrorCode.TokenInvalid,
+    status: 404,
+  });
+}
+
+export function resetOAuthNegativeCache(): void {
+  cache.clear();
+}
diff --git a/packages/backend/src/tokens/request.ts b/packages/backend/src/tokens/request.ts
index 415f1e4e0b6..642cc781ada 100644
--- a/packages/backend/src/tokens/request.ts
+++ b/packages/backend/src/tokens/request.ts
@@ -14,7 +14,18 @@ import { AuthErrorReason, handshake, signedIn, signedOut, signedOutInvalidToken
 import { createClerkRequest } from './clerkRequest';
 import { getCookieName, getCookieValue } from './cookie';
 import { HandshakeService } from './handshake';
-import { getMachineTokenType, isMachineJwt, isMachineToken, isTokenTypeAccepted } from './machine';
+import {
+  getMachineTokenType,
+  isMachineJwt,
+  isMachineToken,
+  isOAuthTokenByPrefix,
+  isTokenTypeAccepted,
+} from './machine';
+import {
+  isOAuthTokenCachedAsInvalid,
+  makeCachedInvalidOAuthTokenError,
+  maybeCacheOAuthTokenAsInvalid,
+} from './oauthNegativeCache';
 import { OrganizationMatcher } from './organizationMatcher';
 import type { MachineTokenType, SessionTokenType } from './tokenTypes';
 import { TokenType } from './tokenTypes';
@@ -795,8 +806,15 @@ export const authenticateRequest: AuthenticateRequest = (async (
       return mismatchState;
     }
 
+    if (isOAuthTokenByPrefix(tokenInHeader) && isOAuthTokenCachedAsInvalid(tokenInHeader)) {
+      return handleMachineError(parsedTokenType, makeCachedInvalidOAuthTokenError());
+    }
+
     const { data, tokenType, errors } = await verifyMachineAuthToken(tokenInHeader, authenticateContext);
     if (errors) {
+      if (isOAuthTokenByPrefix(tokenInHeader)) {
+        maybeCacheOAuthTokenAsInvalid(errors[0], tokenInHeader);
+      }
       return handleMachineError(tokenType, errors[0]);
     }
     return signedIn({
@@ -822,8 +840,15 @@ export const authenticateRequest: AuthenticateRequest = (async (
         return mismatchState;
       }
 
+      if (isOAuthTokenByPrefix(tokenInHeader) && isOAuthTokenCachedAsInvalid(tokenInHeader)) {
+        return handleMachineError(parsedTokenType, makeCachedInvalidOAuthTokenError());
+      }
+
       const { data, tokenType, errors } = await verifyMachineAuthToken(tokenInHeader, authenticateContext);
       if (errors) {
+        if (isOAuthTokenByPrefix(tokenInHeader)) {
+          maybeCacheOAuthTokenAsInvalid(errors[0], tokenInHeader);
+        }
         return handleMachineError(tokenType, errors[0]);
       }