diff --git a/src/providers/key-failover.ts b/src/providers/key-failover.ts
index d5ccd759e3e..701540b8d1d 100644
--- a/src/providers/key-failover.ts
+++ b/src/providers/key-failover.ts
@@ -29,6 +29,153 @@ interface KeyCooldown {
 const DEFAULT_COOLDOWN_MS = 60_000;
 const MAX_COOLDOWN_MS = 10 * 60_000; // cap at 10 min for api-key rotation
 
+/**
+ * Cap for a cooldown the upstream itself dated, as opposed to one we inferred.
+ *
+ * `MAX_COOLDOWN_MS` is deliberately short because an undated 429 is a guess: ten
+ * minutes bounds how long a transient limit can park a working key. A free-tier
+ * quota is not a guess — OpenRouter replies `Weekly/Monthly Limit Exhausted ...
+ * will reset at <date>`, and until that date the key cannot serve anything. Held
+ * for ten minutes instead, it comes back, takes a 429, and rotates again, every
+ * ten minutes for the rest of the week (#4024).
+ *
+ * 32 days rather than unbounded. The wording this parses is
+ * `Weekly/Monthly Limit Exhausted`, so the cap has to clear a monthly window —
+ * 31 days plus a day of slack for timezone and month length. An earlier 8-day
+ * cap looked generous against the weekly case in the issue and silently clamped
+ * every monthly reset to ~23 days early, which puts the key back into exactly
+ * the 429 loop this exists to stop. Caught by the cap's own test.
+ *
+ * Bounded at all because the date is upstream-controlled input: a malformed or
+ * hostile `reset at 2999-01-01` must not park a working key past any horizon an
+ * operator would think to look at.
+ */
+const MAX_QUOTA_COOLDOWN_MS = 32 * 24 * 60 * 60_000;
+
+/**
+ * Read a bounded prefix of a 429 body and pull the upstream's declared reset instant.
+ *
+ * Clones first: the caller still cancels the original body to release the socket,
+ * and a rotation storm must not be gated on reading N full error payloads. Any
+ * failure — no body, already consumed, slow, malformed — returns undefined and
+ * leaves the `Retry-After` path exactly as it was.
+ */
+export async function readQuotaResetAt(
+  response: Response,
+  now = Date.now(),
+): Promise<{ at: number | undefined; response: Response }> {
+  if (!response.body) return { at: undefined, response };
+  try {
+    const reader = response.body.getReader();
+    const decoder = new TextDecoder();
+    const chunks: Uint8Array[] = [];
+    let seen = 0;
+    let text = "";
+    while (seen < QUOTA_RESET_SCAN_BYTES) {
+      const { done, value } = await reader.read();
+      if (done) break;
+      chunks.push(value);
+      seen += value.byteLength;
+      text += decoder.decode(value, { stream: true });
+    }
+    // Hand back a Response carrying the bytes already pulled followed by whatever
+    // is left, so the caller can still read or cancel it. `response.clone()` is
+    // NOT usable here: it tees, and with the original branch undrained the tee
+    // stalls once its buffer fills — a 5MB error body hangs the rotation path,
+    // which is worse than the unbounded read this replaced.
+    const rest = new ReadableStream<Uint8Array>({
+      start(controller) {
+        for (const c of chunks) controller.enqueue(c);
+      },
+      async pull(controller) {
+        const { done, value } = await reader.read();
+        if (done) {
+          controller.close();
+          return;
+        }
+        controller.enqueue(value);
+      },
+      cancel(reason) {
+        return reader.cancel(reason);
+      },
+    });
+    const rebuilt = new Response(rest, {
+      status: response.status,
+      statusText: response.statusText,
+      headers: response.headers,
+    });
+    return { at: parseQuotaResetAt(text, now), response: rebuilt };
+  } catch {
+    return { at: undefined, response };
+  }
+}
+
+/**
+ * How much of a 429 body is read and scanned for the reset instant.
+ *
+ * Bounds the READ, not just the parse: this runs on the rotation path, once per
+ * rotated key under a rate-limit storm, and the body is upstream-controlled.
+ * OpenRouter's rate_limit_error JSON is a few hundred bytes.
+ */
+const QUOTA_RESET_SCAN_BYTES = 4_096;
+
+/**
+ * Reset instant an upstream declared in a 429 *body*, in epoch ms.
+ *
+ * Only the body carries this: OpenRouter sends no `Retry-After` for a quota
+ * exhaustion, so the header path (`parseRetryAfterMs`) sees nothing and falls
+ * back to `DEFAULT_COOLDOWN_MS`. Returns undefined for anything it cannot read
+ * as a date, so an unparsable body keeps today's behaviour exactly.
+ */
+/**
+ * Whether `YYYY-MM-DD…` names a day that exists.
+ *
+ * `Date.parse` does NOT reject an out-of-range day: measured on Bun,
+ * `2026-02-30T00:00:00Z` yields March 2 and `2026-04-31T00:00:00Z` yields
+ * May 1, so a malformed upstream body would park a key past the instant it
+ * actually named. Only the month is rejected outright (`2026-13-01` is NaN).
+ *
+ * Checked on the date text alone rather than by round-tripping the parsed
+ * instant, because a value carrying an explicit offset (`…T23:00+05:30`)
+ * legitimately lands on a different UTC day than the one written.
+ */
+function isRealCalendarDate(value: string): boolean {
+  const [year, month, day] = value.slice(0, 10).split("-").map(Number);
+  if (month < 1 || month > 12 || day < 1) return false;
+  const leap = (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;
+  const lengths = [31, leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
+  return day <= lengths[month - 1]!;
+}
+
+export function parseQuotaResetAt(body: string | null | undefined, now = Date.now()): number | undefined {
+  const text = body?.slice(0, QUOTA_RESET_SCAN_BYTES);
+  if (!text) return undefined;
+  // `will reset at 2026-09-09 03:30:06` / `... at 2026-09-09T03:30:06Z` / `resets at <date>`
+  const match = /reset[s]?\s+at\s+([0-9]{4}-[0-9]{2}-[0-9]{2}(?:[T ][0-9]{2}:[0-9]{2}(?::[0-9]{2})?(?:\.[0-9]+)?(?:Z|[+-][0-9]{2}:?[0-9]{2})?)?)/i.exec(text);
+  if (!match) return undefined;
+  // Pin a bare `YYYY-MM-DD hh:mm:ss` to UTC explicitly.
+  //
+  // ECMA-262 says a date-TIME form with no offset is LOCAL time, and Node follows
+  // that: `Date.parse("2026-09-09 03:30:06")` differs from the UTC reading by the
+  // host offset (7h on a PDT box, measured). Bun currently returns the UTC value
+  // for the same string, so on this runtime the normalisation is a no-op today —
+  // which is exactly why it is written out rather than relied upon. If Bun ever
+  // conforms, an un-normalised parse would silently shift every park-until by the
+  // operator's offset, and the early direction resumes the 429 loop.
+  //
+  // A consequence worth knowing: no Bun test can observe this branch being
+  // removed. The explicit-zone case below is the part the suite can pin.
+  const raw = match[1].includes("T") || /(?:Z|[+-][0-9]{2}:?[0-9]{2})$/.test(match[1])
+    ? match[1]
+    : `${match[1].replace(" ", "T")}Z`;
+  if (!isRealCalendarDate(match[1])) return undefined;
+  const at = Date.parse(raw);
+  if (!Number.isFinite(at)) return undefined;
+  // Already past, or beyond the cap: not usable as a park-until instant.
+  if (at <= now) return undefined;
+  return Math.min(at, now + MAX_QUOTA_COOLDOWN_MS);
+}
+
 /**
  * Default same-target 429 retry policy used when a provider opts in via a bare
  * `retryOn429: {}` (presence = opt-in with these defaults).
@@ -363,6 +510,7 @@ function rotateKeyAfterFailure(
   now = Date.now(),
   attemptedKey?: string,
   attemptedSelection?: ProviderApiKeySelection,
+  quotaResetAt?: number,
 ): OcxProviderConfig | null {
   const provider = config.providers[providerName];
   if (!provider) return null;
@@ -421,7 +569,12 @@ function rotateKeyAfterFailure(
     // full cap instead of the 429 default so a dead key is not re-tried once a minute.
     const cooldownMs = failureStatus === 401
       ? MAX_COOLDOWN_MS
-      : parseRetryAfterMs(retryAfterHeader, now) ?? DEFAULT_COOLDOWN_MS;
+      // A reset instant the upstream dated outranks both the header and the
+      // default: it is the only one of the three that knows when the quota
+      // actually returns (#4024).
+      : quotaResetAt !== undefined
+        ? Math.max(quotaResetAt - now, 1)
+        : parseRetryAfterMs(retryAfterHeader, now) ?? DEFAULT_COOLDOWN_MS;
     keyCooldowns.set(cooldownKey(providerName, outcome.value.failedId), { cooldownUntil: now + cooldownMs });
     sweepExpiredOnWrite(now);
   }
@@ -448,8 +601,9 @@ export function rotateKeyOn429(
   now = Date.now(),
   attemptedKey?: string,
   attemptedSelection?: ProviderApiKeySelection,
+  quotaResetAt?: number,
 ): OcxProviderConfig | null {
-  return rotateKeyAfterFailure(config, providerName, 429, retryAfterHeader, now, attemptedKey, attemptedSelection);
+  return rotateKeyAfterFailure(config, providerName, 429, retryAfterHeader, now, attemptedKey, attemptedSelection, quotaResetAt);
 }
 
 /**
@@ -482,6 +636,8 @@ export function sweepExpiredApiKeyCooldowns(now = Date.now()): number {
 
 interface RotateProviderTransportOptions {
   retryAfter?: string | null;
+  /** Epoch ms from `parseQuotaResetAt`, when the upstream dated the reset in its body. */
+  quotaResetAt?: number;
   now?: number;
   attemptedKey?: string;
   attemptedSelection?: ProviderApiKeySelection;
@@ -507,6 +663,7 @@ export function rotateProviderTransportOn429(
     options.now,
     options.attemptedKey,
     options.attemptedSelection ?? routedProvider._apiKeyAttempt,
+    options.quotaResetAt,
   );
   if (!rotated) return null;
   return applyRotatedTransport(providerName, routedProvider, rotated, options.promptCacheKey);
diff --git a/src/server/responses/adapter-dispatch.ts b/src/server/responses/adapter-dispatch.ts
index c26b77b19b8..b1f161c84eb 100644
--- a/src/server/responses/adapter-dispatch.ts
+++ b/src/server/responses/adapter-dispatch.ts
@@ -25,6 +25,7 @@ import {
   hasKeyPoolFailover,
   rotateProviderTransportOn401,
   rateLimitRetryDelayMs,
+  readQuotaResetAt,
   rotateProviderTransportOn429,
 } from "../../providers/key-failover";
 import {
@@ -667,11 +668,20 @@ export async function prepareAdapterExchange(
       // SAME request once per remaining key. OAuth/forward providers and single-key pools
       // return null immediately, so this stays a no-op for them (src/providers/key-failover.ts).
       while (upstreamResponse.status === 429 && hasKeyPoolFailover(route.provider)) {
+        // A quota exhaustion is dated in the BODY, not in `Retry-After` — OpenRouter
+        // sends no header for it (#4024). Read a bounded prefix before the socket is
+        // released below; a failed or slow read just leaves the header path in charge.
+        // Peeks a bounded prefix and hands back a Response still carrying the whole
+        // body, so the cancel below still releases the socket.
+        const peeked = await readQuotaResetAt(upstreamResponse);
+        upstreamResponse = peeked.response;
+        const quotaResetAt = peeked.at;
         const rotated = rotateProviderTransportOn429(config, route.providerName, route.provider, {
           retryAfter: upstreamResponse.headers.get("retry-after"),
           now: Date.now(),
           attemptedKey: route.provider.apiKey,
           promptCacheKey: parsed.options.promptCacheKey,
+          quotaResetAt,
         });
         if (!rotated) break;
         // Release the failed response's socket before retrying; unread bodies otherwise linger
diff --git a/tests/providers/openrouter-quota-reset-cooldown-4024.test.ts b/tests/providers/openrouter-quota-reset-cooldown-4024.test.ts
new file mode 100644
index 00000000000..d806bed1df0
--- /dev/null
+++ b/tests/providers/openrouter-quota-reset-cooldown-4024.test.ts
@@ -0,0 +1,154 @@
+import { describe, expect, test } from "bun:test";
+import { parseQuotaResetAt, readQuotaResetAt } from "../../src/providers/key-failover";
+
+/**
+ * #4024 — a free-tier quota exhaustion is dated by the upstream, and OpenRouter
+ * sends it in the 429 body rather than in `Retry-After`. Without reading it the
+ * key is parked for the undated-429 cap (10 min), comes back, takes another 429,
+ * and repeats for the rest of the quota window.
+ */
+describe("parseQuotaResetAt", () => {
+  const now = Date.parse("2026-09-01T00:00:00Z");
+
+  test("reads the OpenRouter wording, treating a bare timestamp as UTC", () => {
+    const body = JSON.stringify({
+      error: { code: "rate_limit_error", message: "Weekly Limit Exhausted. Your limit will reset at 2026-09-09 03:30:06" },
+    });
+    expect(parseQuotaResetAt(body, now)).toBe(Date.parse("2026-09-09T03:30:06Z"));
+  });
+
+  test("honours an explicit zone rather than re-stamping it as UTC", () => {
+    const at = parseQuotaResetAt("limit will reset at 2026-09-09T03:30:06+05:30", now);
+    expect(at).toBe(Date.parse("2026-09-09T03:30:06+05:30"));
+    expect(at).not.toBe(Date.parse("2026-09-09T03:30:06Z"));
+  });
+
+  test("accepts the 'resets at' spelling and a date with no clock time", () => {
+    expect(parseQuotaResetAt("quota resets at 2026-09-09", now)).toBe(Date.parse("2026-09-09T00:00:00Z"));
+  });
+
+  test("a body it cannot read yields undefined, so today's behaviour is unchanged", () => {
+    for (const body of [
+      null,
+      undefined,
+      "",
+      "429 Too Many Requests",
+      JSON.stringify({ error: { message: "rate limited, try later" } }),
+      "will reset at soon",
+      "will reset at 2026-13-45 99:99:99",
+    ]) {
+      expect(parseQuotaResetAt(body as string | null | undefined, now)).toBeUndefined();
+    }
+  });
+
+  test("a reset already in the past is not a park-until instant", () => {
+    expect(parseQuotaResetAt("will reset at 2026-08-01 00:00:00", now)).toBeUndefined();
+  });
+
+  test("a monthly window is honoured in full, not clamped", () => {
+    // `Weekly/Monthly Limit Exhausted` is the wording upstream sends, so a reset
+    // up to ~31 days out is legitimate. Clamping it would resume the 429 loop
+    // weeks early — the failure this feature exists to prevent.
+    const monthly = "will reset at 2026-10-01 00:00:00";
+    expect(parseQuotaResetAt(monthly, now)).toBe(Date.parse("2026-10-01T00:00:00Z"));
+  });
+
+  test("an absurd or hostile date is capped rather than parking the key forever", () => {
+    const at = parseQuotaResetAt("will reset at 2999-01-01 00:00:00", now);
+    expect(at).toBe(now + 32 * 24 * 60 * 60_000);
+  });
+
+  test("a day the calendar does not have is refused, not rolled forward", () => {
+    // `Date.parse` does not reject an out-of-range DAY — measured on Bun,
+    // `2026-02-30T00:00:00Z` yields March 2 — so without this the key parks
+    // past the instant the upstream actually named. Only the month is caught
+    // by the parser itself.
+    const feb = Date.parse("2026-02-25T00:00:00Z");
+    expect(parseQuotaResetAt("resets at 2026-02-30T00:00:00Z", feb)).toBeUndefined();
+    expect(parseQuotaResetAt("resets at 2026-02-29T00:00:00Z", feb)).toBeUndefined();
+    expect(parseQuotaResetAt("resets at 2026-04-31T00:00:00Z", Date.parse("2026-04-25T00:00:00Z"))).toBeUndefined();
+    expect(parseQuotaResetAt("resets at 2026-13-01T00:00:00Z", feb)).toBeUndefined();
+  });
+
+  test("real leap days still park the key, including the century rule", () => {
+    // The guard above must not cost a legitimate Feb 29. 2024 is a leap year,
+    // 2000 is one (divisible by 400) and 2100 is not (divisible by 100).
+    expect(parseQuotaResetAt("resets at 2024-02-29T00:00:00Z", Date.parse("2024-02-25T00:00:00Z")))
+      .toBe(Date.parse("2024-02-29T00:00:00Z"));
+    expect(parseQuotaResetAt("resets at 2000-02-29T00:00:00Z", Date.parse("2000-02-25T00:00:00Z")))
+      .toBe(Date.parse("2000-02-29T00:00:00Z"));
+    expect(parseQuotaResetAt("resets at 2100-02-29T00:00:00Z", Date.parse("2100-02-25T00:00:00Z")))
+      .toBeUndefined();
+  });
+
+  test("only the first 4KB is scanned, so a huge body cannot stall the rotation path", () => {
+    const padded = "x".repeat(8_000) + " will reset at 2026-09-09 03:30:06";
+    expect(parseQuotaResetAt(padded, now)).toBeUndefined();
+  });
+});
+
+describe("readQuotaResetAt", () => {
+  const now = Date.parse("2026-09-01T00:00:00Z");
+
+  test("returns the reset AND a response whose body is still fully readable", async () => {
+    // The caller still needs this response: on a failed rotation adapter-dispatch
+    // breaks out of the loop with it, and on a successful one it cancels the body
+    // to release the socket. Peeking must not cost it either.
+    const body = JSON.stringify({
+      error: { code: "rate_limit_error", message: "Weekly Limit Exhausted. Your limit will reset at 2026-09-05 12:00:00" },
+    });
+    const { at, response } = await readQuotaResetAt(new Response(body, { status: 429 }), now);
+
+    expect(at).toBe(Date.parse("2026-09-05T12:00:00Z"));
+    expect(response.status).toBe(429);
+    // The bytes already pulled are replayed ahead of the remainder.
+    expect(await response.text()).toBe(body);
+  });
+
+  test("the returned response can be cancelled instead of read", async () => {
+    const { response } = await readQuotaResetAt(new Response("x".repeat(10_000), { status: 429 }), now);
+    await response.body?.cancel();
+    expect(response.bodyUsed).toBe(true);
+  });
+
+  test("a bodyless or unreadable response leaves the Retry-After path in charge", async () => {
+    expect((await readQuotaResetAt(new Response(null, { status: 429 }), now)).at).toBeUndefined();
+    const consumed = new Response("x", { status: 429 });
+    await consumed.text();
+    expect((await readQuotaResetAt(consumed, now)).at).toBeUndefined();
+  });
+});
+
+describe("readQuotaResetAt — the read is bounded, not just the parse", () => {
+  const now = Date.parse("2026-09-01T00:00:00Z");
+
+  test("stops pulling after the cap instead of buffering the whole body", async () => {
+    // A chatty upstream must not make the rotation path read megabytes. This counts
+    // what the reader actually PULLED, not what the parser looked at — the two were
+    // different before this was fixed (`.text()` read it all, then sliced 4KB).
+    let pulled = 0;
+    const chunk = new TextEncoder().encode("x".repeat(64 * 1_024));
+    const total = 5 * 1_024 * 1_024;
+    const body = new ReadableStream<Uint8Array>({
+      pull(controller) {
+        if (pulled >= total) {
+          controller.close();
+          return;
+        }
+        pulled += chunk.byteLength;
+        controller.enqueue(chunk);
+      },
+    });
+
+    const { at } = await readQuotaResetAt(new Response(body, { status: 429 }), now);
+
+    expect(at).toBeUndefined();
+    expect(pulled).toBeLessThan(total / 4);
+  });
+
+  test("still finds a reset that sits inside the cap", async () => {
+    const body = `{"error":{"message":"Weekly Limit Exhausted. Your limit will reset at 2026-09-05 12:00:00"}}`;
+    expect((await readQuotaResetAt(new Response(body, { status: 429 }), now)).at)
+      .toBe(Date.parse("2026-09-05T12:00:00Z"));
+  });
+});
diff --git a/tests/server/server-key-failover-e2e.test.ts b/tests/server/server-key-failover-e2e.test.ts
index 4bf924c2492..9fe34cb8f40 100644
--- a/tests/server/server-key-failover-e2e.test.ts
+++ b/tests/server/server-key-failover-e2e.test.ts
@@ -5,7 +5,7 @@ import { join } from "node:path";
 import { apiKeyAccountLogLabel } from "../../src/codex/account-label";
 import { readUsageEntries, resetUsageReadCacheForTests } from "../../src/usage/log";
 import { loadConfig, saveConfig } from "../../src/config";
-import { clearKeyCooldowns, rotateKeyOn429 } from "../../src/providers/key-failover";
+import { clearKeyCooldowns, getKeyCooldownUntil, rotateKeyOn429 } from "../../src/providers/key-failover";
 import { deriveXaiConvId } from "../../src/providers/xai-transport";
 import { clearReasoningReplayCacheForTests } from "../../src/responses/reasoning-replay-cache";
 import { startServer } from "../../src/server";
@@ -496,6 +496,69 @@ describe("server 429 key failover (end-to-end)", () => {
   });
   }
 
+  test("a 429 dated in the body parks the failed key until that instant, outranking Retry-After", async () => {
+    // #4024 regression, through the real dispatch path. The unit tests cover
+    // parseQuotaResetAt/readQuotaResetAt in isolation; nothing exercised
+    // adapter-dispatch actually READING the body and handing quotaResetAt to
+    // rotateProviderTransportOn429. Dropping it there would leave every unit
+    // test green while the key came back after the header's 30s and took the
+    // same 429 again — which is the bug.
+    const resetAt = new Date(Date.now() + 6 * 60 * 60_000);
+    const stamp = resetAt.toISOString().replace("T", " ").slice(0, 19); // bare form, read as UTC
+    const seenAuth: string[] = [];
+    upstream = Bun.serve({
+      hostname: "127.0.0.1", port: 0,
+      fetch(req) {
+        seenAuth.push(req.headers.get("authorization") ?? "");
+        if (seenAuth.length === 1) {
+          return new Response(JSON.stringify({
+            error: { code: "rate_limit_error", message: `Weekly Limit Exhausted. Your limit will reset at ${stamp}` },
+          }), { status: 429, headers: { "retry-after": "30", "content-type": "application/json" } });
+        }
+        return new Response(JSON.stringify({
+          id: "chatcmpl-dated", object: "chat.completion",
+          choices: [{ index: 0, message: { role: "assistant", content: "ok after dated rotate" }, finish_reason: "stop" }],
+        }), { headers: { "content-type": "application/json" } });
+      },
+    });
+    const config: OcxConfig = {
+      port: 0, hostname: "127.0.0.1", defaultProvider: "dated",
+      providers: {
+        dated: {
+          adapter: "openai-chat",
+          baseUrl: `http://127.0.0.1:${upstream.port}/v1`,
+          allowPrivateNetwork: true,
+          apiKey: "key-dated-000111222333",
+          apiKeyPool: [
+            { id: "d1", key: "key-dated-000111222333", addedAt: 1 },
+            { id: "d2", key: "key-dated-444555666777", addedAt: 2 },
+          ],
+        },
+      },
+    } as OcxConfig;
+    saveConfig(config);
+    const server = startServer(0);
+    try {
+      const res = await fetch(new URL("/v1/responses", server.url), {
+        method: "POST",
+        headers: { "content-type": "application/json" },
+        body: JSON.stringify({ model: "dated/some-model", input: "hello", stream: false }),
+      });
+      expect(res.status).toBe(200);
+      await res.json();
+      expect(seenAuth[1]).toBe("Bearer key-dated-444555666777");
+
+      const cooldownUntil = getKeyCooldownUntil("dated", "d1");
+      expect(cooldownUntil).not.toBeNull();
+      // The body's instant, not the header's 30s. Compared with a wide window
+      // because the cooldown is anchored to the server's Date.now(), not ours.
+      expect(cooldownUntil!).toBeGreaterThan(Date.now() + 5 * 60 * 60_000);
+      expect(cooldownUntil!).toBeLessThanOrEqual(resetAt.getTime() + 60_000);
+    } finally {
+      await server.stop(true);
+    }
+  });
+
   test("reasoning replay misses after a 429 rotates to a different physical key", async () => {
     const model = "reasoning-model";
     const callId = "call_key_rotation";