diff --git a/lib/src/access/access-fetch.ts b/lib/src/access/access-fetch.ts
index f25627e29..b5a22ad7a 100644
--- a/lib/src/access/access-fetch.ts
+++ b/lib/src/access/access-fetch.ts
@@ -6,8 +6,10 @@ import {
   NetworkError,
   PermissionDeniedError,
   ServiceError,
+  TokenExpiredError,
   UnauthenticatedError,
 } from '../errors.js';
+import { readJwtExpMs } from '../auth/interceptors.js';
 import { validateSecureUrl } from '../utils.js';
 
 export type RewrapRequest = {
@@ -21,6 +23,32 @@ export type RewrapResponseLegacy = {
   schemaVersion: string;
 };
 
+/**
+ * Classify a rewrap 401. When the `Authorization` header this SDK STAMPED on the request
+ * carries a JWT that was already expired (by local clock) as the request went out, the 401
+ * is the well-known static-token-provider footgun — surfaced as {@link TokenExpiredError},
+ * which has a clear recovery path (refresh the token and retry) and must not be conflated
+ * with an authorization denial. Anything else — an opaque token, an unreadable JWT, a
+ * still-valid `exp` — classifies as the generic {@link UnauthenticatedError}: an expired
+ * stamp is the ONLY trigger, so the specific error is zero-false-positive.
+ */
+function classifyRewrap401(
+  headers: Record<string, string> | undefined,
+  url: string
+): UnauthenticatedError {
+  const auth = headers?.['Authorization'] ?? headers?.['authorization'];
+  const match = typeof auth === 'string' ? auth.match(/^(?:Bearer|DPoP)\s+(.+)$/i) : null;
+  const expMs = match ? readJwtExpMs(match[1]) : undefined;
+  if (expMs !== undefined && expMs <= Date.now()) {
+    return new TokenExpiredError(
+      `401 for [${url}]; rewrap auth failure: the stamped access token was already EXPIRED — ` +
+        'refresh it and retry (see refreshTokenProvider / clientCredentialsTokenProvider / ' +
+        'externalJwtTokenProvider)'
+    );
+  }
+  return new UnauthenticatedError(`401 for [${url}]; rewrap auth failure`);
+}
+
 /**
  * Get a rewrapped access key to the document, if possible
  * @param url Key access server rewrap endpoint
@@ -66,7 +94,9 @@ export async function fetchWrappedKey(
           `400 for [${req.url}]: rewrap bad request [${await response.text()}]`
         );
       case 401:
-        throw new UnauthenticatedError(`401 for [${req.url}]; rewrap auth failure`);
+        // Distinguish the static-token-provider footgun (expired stamp -> TokenExpiredError,
+        // recoverable by refresh+retry) from a generic auth failure. See classifyRewrap401.
+        throw classifyRewrap401(req.headers, req.url);
       case 403:
         throw new PermissionDeniedError(
           `403 for [${req.url}]; rewrap permission denied: forbidden`
diff --git a/lib/src/auth/interceptors.ts b/lib/src/auth/interceptors.ts
index c0a0f7971..2fef9aea9 100644
--- a/lib/src/auth/interceptors.ts
+++ b/lib/src/auth/interceptors.ts
@@ -12,6 +12,57 @@ import { base64 } from '../encodings/index.js';
  */
 export type TokenProvider = () => Promise<string>;
 
+/**
+ * Read a JWT's `exp` claim as epoch-milliseconds, WITHOUT verifying the signature.
+ * Returns undefined for opaque (non-JWT) tokens or an unreadable payload — so the
+ * expiry footgun check below is skipped rather than firing a false positive.
+ */
+export function readJwtExpMs(token: string): number | undefined {
+  const parts = token.split('.');
+  if (parts.length !== 3) return undefined;
+  try {
+    let b64 = parts[1].replace(/-/g, '+').replace(/_/g, '/');
+    while (b64.length % 4 !== 0) b64 += '=';
+    const { exp } = JSON.parse(atob(b64)) as { exp?: number };
+    return typeof exp === 'number' ? exp * 1000 : undefined;
+  } catch {
+    return undefined;
+  }
+}
+
+/**
+ * A common footgun: passing a *static* token getter (e.g. `() => myToken`) to an interceptor.
+ * The interceptor faithfully stamps that token on every request, but a static getter never
+ * refreshes — so once the (typically short-lived) access token expires, every request goes out
+ * with a dead Bearer and the platform answers HTTP 401. Callers routinely mis-diagnose that 401
+ * as an authorization / "access denied" failure and lose hours to it.
+ *
+ * A correctly-refreshing provider NEVER returns an already-expired token, so an expired token is
+ * an unambiguous, zero-false-positive signal of the footgun. This factory returns a guard that
+ * emits ONE actionable `console.warn` the first time it sees an expired JWT and then stays quiet
+ * (no log spam). It never throws and silently ignores opaque tokens whose expiry can't be read.
+ */
+function makeExpiredTokenWarner(interceptorName: string): (token: string) => void {
+  let warned = false;
+  return (token: string) => {
+    if (warned) return;
+    const expMs = readJwtExpMs(token);
+    if (expMs !== undefined && expMs <= Date.now()) {
+      warned = true;
+      // eslint-disable-next-line no-console
+      console.warn(
+        `[OpenTDF] ${interceptorName} received an already-EXPIRED access token. Your ` +
+          '`tokenProvider` is returning a token it never refreshes, so platform requests will ' +
+          'fail with HTTP 401 — frequently mis-diagnosed as an authorization / "access denied" ' +
+          'error. Fix: wrap a refreshing provider — refreshTokenProvider(), ' +
+          'clientCredentialsTokenProvider(), or externalJwtTokenProvider() — or refresh inside ' +
+          'your own tokenProvider so it never returns an expired token. ' +
+          'Docs: https://github.com/opentdf/web-sdk#authentication'
+      );
+    }
+  };
+}
+
 /**
  * Options for creating a DPoP-aware auth interceptor.
  */
@@ -49,8 +100,10 @@ export type DPoPInterceptor = Interceptor & {
  * ```
  */
 export function authTokenInterceptor(tokenProvider: TokenProvider): Interceptor {
+  const warnIfExpired = makeExpiredTokenWarner('authTokenInterceptor');
   return (next) => async (req) => {
     const token = await tokenProvider();
+    warnIfExpired(token);
     req.header.set('Authorization', `Bearer ${token}`);
     return next(req);
   };
@@ -81,9 +134,11 @@ export function authTokenDPoPInterceptor(options: DPoPInterceptorOptions): DPoPI
   const dpopKeysPromise: Promise<KeyPair> = options.dpopKeys
     ? Promise.resolve(options.dpopKeys)
     : cryptoService.generateSigningKeyPair();
+  const warnIfExpired = makeExpiredTokenWarner('authTokenDPoPInterceptor');
 
   const interceptor: Interceptor = (next) => async (req) => {
     const [token, keys] = await Promise.all([options.tokenProvider(), dpopKeysPromise]);
+    warnIfExpired(token);
 
     const url = new URL(req.url);
     const httpUri = `${url.origin}${url.pathname}`;
diff --git a/lib/src/errors.ts b/lib/src/errors.ts
index af46bb80e..1afc54323 100644
--- a/lib/src/errors.ts
+++ b/lib/src/errors.ts
@@ -100,6 +100,22 @@ export class UnauthenticatedError extends TdfError {
   override name = 'UnauthenticatedError';
 }
 
+/**
+ * Authentication failure (401) where the access token this SDK stamped on the request was
+ * ALREADY EXPIRED (by local clock) when the platform rejected it — the static-token-provider
+ * footgun surfaced as a typed error. Unlike a generic 401, and very unlike a
+ * `PermissionDeniedError`, this failure has a clear recovery path: obtain a fresh access
+ * token (e.g. via `refreshTokenProvider` / `clientCredentialsTokenProvider`) and retry.
+ * Callers surfacing access verdicts should treat it as "no decision — retry", never as an
+ * authorization DENY.
+ *
+ * Subclasses `UnauthenticatedError`, so existing `instanceof UnauthenticatedError` handling
+ * continues to match (non-breaking).
+ */
+export class TokenExpiredError extends UnauthenticatedError {
+  override name = 'TokenExpiredError';
+}
+
 /** Authorization failure (403) */
 export class PermissionDeniedError extends TdfError {
   override name = 'PermissionDeniedError';
diff --git a/lib/tests/web/access/access-fetch.test.ts b/lib/tests/web/access/access-fetch.test.ts
index abdba1c86..9f93bb833 100644
--- a/lib/tests/web/access/access-fetch.test.ts
+++ b/lib/tests/web/access/access-fetch.test.ts
@@ -13,6 +13,7 @@ import {
   NetworkError,
   PermissionDeniedError,
   ServiceError,
+  TokenExpiredError,
   UnauthenticatedError,
 } from '../../../src/errors.js';
 import { OriginAllowList } from '../../../src/access.js';
@@ -113,10 +114,68 @@ describe('access-fetch.js', () => {
         expect.fail('Should have thrown');
       } catch (e) {
         expect(e).to.be.instanceOf(UnauthenticatedError);
+        // an OPAQUE stamped token ('Bearer test-token') carries no readable expiry, so the
+        // 401 must stay the GENERIC auth failure — never the expired-token classification.
+        expect(e).to.not.be.instanceOf(TokenExpiredError);
         expect(e.message).to.equal(`401 for [${url}]; rewrap auth failure`);
       }
     });
 
+    /** Build an unsigned JWT whose `exp` is `deltaSeconds` from now (negative = expired). */
+    const makeJwt = (deltaSeconds: number): string => {
+      const b64url = (o: unknown): string =>
+        btoa(JSON.stringify(o)).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
+      const exp = Math.floor(Date.now() / 1000) + deltaSeconds;
+      return `${b64url({ alg: 'none' })}.${b64url({ exp })}.sig`;
+    };
+
+    /** An auth provider that stamps a specific Authorization header value. */
+    const providerStamping = (authorization: string): AuthProvider =>
+      ({
+        withCreds: async (req: { headers?: Record<string, string> }) => ({
+          ...req,
+          headers: { ...req.headers, Authorization: authorization },
+        }),
+      }) as unknown as AuthProvider;
+
+    it('should throw TokenExpiredError when the 401 request was stamped with an EXPIRED JWT', async () => {
+      fetchStub.returns(createMockResponse('Auth failed', false, 401, 'Unauthorized'));
+
+      try {
+        await fetchWrappedKey(url, requestBody, providerStamping(`Bearer ${makeJwt(-60)}`));
+        expect.fail('Should have thrown');
+      } catch (e) {
+        // the typed footgun signal — AND still an UnauthenticatedError, so existing
+        // instanceof handling keeps matching (non-breaking subclass).
+        expect(e).to.be.instanceOf(TokenExpiredError);
+        expect(e).to.be.instanceOf(UnauthenticatedError);
+        expect(e.message).to.contain('EXPIRED');
+      }
+    });
+
+    it('should throw plain UnauthenticatedError when the 401 request carried a still-VALID JWT', async () => {
+      fetchStub.returns(createMockResponse('Auth failed', false, 401, 'Unauthorized'));
+
+      try {
+        await fetchWrappedKey(url, requestBody, providerStamping(`Bearer ${makeJwt(300)}`));
+        expect.fail('Should have thrown');
+      } catch (e) {
+        expect(e).to.be.instanceOf(UnauthenticatedError);
+        expect(e).to.not.be.instanceOf(TokenExpiredError);
+      }
+    });
+
+    it('should classify a DPoP-scheme expired stamp the same as Bearer', async () => {
+      fetchStub.returns(createMockResponse('Auth failed', false, 401, 'Unauthorized'));
+
+      try {
+        await fetchWrappedKey(url, requestBody, providerStamping(`DPoP ${makeJwt(-60)}`));
+        expect.fail('Should have thrown');
+      } catch (e) {
+        expect(e).to.be.instanceOf(TokenExpiredError);
+      }
+    });
+
     it('should throw PermissionDeniedError for a 403 Forbidden response', async () => {
       fetchStub.returns(createMockResponse('Forbidden', false, 403, 'Forbidden'));
 
diff --git a/lib/tests/web/interceptors.test.ts b/lib/tests/web/interceptors.test.ts
index 25ba358cb..adf58c55e 100644
--- a/lib/tests/web/interceptors.test.ts
+++ b/lib/tests/web/interceptors.test.ts
@@ -26,6 +26,15 @@ async function captureHeaders(
   return headers;
 }
 
+/** Build an unsigned JWT whose `exp` is `deltaSeconds` from now (negative = already expired). */
+function makeJwt(deltaSeconds: number): string {
+  const b64url = (o: unknown): string =>
+    btoa(JSON.stringify(o)).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
+  const header = { alg: 'RS256', typ: 'JWT' };
+  const payload = { exp: Math.floor(Date.now() / 1000) + deltaSeconds };
+  return `${b64url(header)}.${b64url(payload)}.unsigned`;
+}
+
 // --- authTokenInterceptor ---
 
 describe('authTokenInterceptor', () => {
@@ -51,6 +60,63 @@ describe('authTokenInterceptor', () => {
   });
 });
 
+// --- expired-token footgun warning ---
+
+describe('authTokenInterceptor expired-token warning', () => {
+  let warnings: string[];
+  let origWarn: typeof console.warn;
+
+  beforeEach(() => {
+    warnings = [];
+    origWarn = console.warn;
+    // eslint-disable-next-line no-console
+    console.warn = (...args: unknown[]) => {
+      warnings.push(args.map((a) => String(a)).join(' '));
+    };
+  });
+
+  afterEach(() => {
+    // eslint-disable-next-line no-console
+    console.warn = origWarn;
+  });
+
+  it('warns ONCE when the tokenProvider returns an already-expired JWT (and still stamps it)', async () => {
+    const expired = makeJwt(-60);
+    const interceptor = authTokenInterceptor(async () => expired);
+
+    const headers = await captureHeaders(interceptor);
+    // Behavior is unchanged — the token is still stamped (non-breaking guard).
+    expect(headers.get('Authorization')).to.equal(`Bearer ${expired}`);
+    expect(warnings).to.have.length(1);
+    expect(warnings[0]).to.include('EXPIRED');
+    expect(warnings[0]).to.include('refreshTokenProvider');
+
+    // A second request must NOT warn again (one-shot, no log spam).
+    await captureHeaders(interceptor);
+    expect(warnings).to.have.length(1);
+  });
+
+  it('does NOT warn for a valid (unexpired) JWT', async () => {
+    const interceptor = authTokenInterceptor(async () => makeJwt(300));
+    await captureHeaders(interceptor);
+    expect(warnings).to.have.length(0);
+  });
+
+  it('does NOT warn for an opaque (non-JWT) token', async () => {
+    const interceptor = authTokenInterceptor(async () => 'opaque-token-abc');
+    const headers = await captureHeaders(interceptor);
+    expect(headers.get('Authorization')).to.equal('Bearer opaque-token-abc');
+    expect(warnings).to.have.length(0);
+  });
+
+  it('also warns for authTokenDPoPInterceptor on an expired token', async () => {
+    const interceptor = authTokenDPoPInterceptor({ tokenProvider: async () => makeJwt(-1) });
+    await captureHeaders(interceptor);
+    expect(warnings).to.have.length(1);
+    expect(warnings[0]).to.include('authTokenDPoPInterceptor');
+  });
+});
+
 // --- authTokenDPoPInterceptor ---
 
 describe('authTokenDPoPInterceptor', () => {