diff --git a/docs-site/src/content/docs/guides/web-dashboard.md b/docs-site/src/content/docs/guides/web-dashboard.md
index 6a57e78fd38..cff84de6197 100644
--- a/docs-site/src/content/docs/guides/web-dashboard.md
+++ b/docs-site/src/content/docs/guides/web-dashboard.md
@@ -72,6 +72,9 @@ The **Codex Auth** page manages the native ChatGPT/Codex route:
   and a strictly lower-usage eligible account exists.
 - New sessions can choose the lowest-usage eligible account. Paid plans score the hottest known 5h,
   weekly, or 30d window; Go/Free plans use the 30d window only.
+- When WHAM supplies `limit_window_seconds`, Codex Auth classifies a primary window of at least 28
+  days as 30d instead of assuming every primary window is weekly. Responses without a duration keep
+  the legacy weekly interpretation.
 - **Refresh quotas** re-reads account usage immediately so routing and the account cards use the same
   values.
 - Pool request logs use opaque labels such as `p3fa91c`, never account emails.
diff --git a/docs-site/src/content/docs/ko/guides/web-dashboard.md b/docs-site/src/content/docs/ko/guides/web-dashboard.md
index 1f8a371fd80..a4510bda6e4 100644
--- a/docs-site/src/content/docs/ko/guides/web-dashboard.md
+++ b/docs-site/src/content/docs/ko/guides/web-dashboard.md
@@ -71,6 +71,8 @@ Dashboard의 **Sub-agent delegation** 선택기는 `injectionModel`과 선택적
   정상 계정이 있으면 그 계정으로 다시 묶일 수 있습니다.
 - 새 세션은 사용량이 가장 낮은 정상 계정을 고를 수 있습니다. 유료 플랜은 알려진 5시간, 주간, 30일
   창 중 가장 높은 사용률로 점수를 매기고, Go/Free 플랜은 30일 창만 사용합니다.
+- WHAM이 `limit_window_seconds`를 제공하면 Codex Auth는 28일 이상인 primary window를 주간이 아닌
+  30일 창으로 분류합니다. 기간이 없는 기존 응답은 이전과 동일하게 주간 창으로 해석합니다.
 - **Refresh quotas**는 계정 사용량을 즉시 다시 읽어 라우팅과 화면의 계정 카드가 같은 값을 보게 합니다.
 - 풀 요청 로그에는 이메일 대신 `p3fa91c` 같은 불투명한 라벨을 사용합니다.
 
diff --git a/src/codex/quota.ts b/src/codex/quota.ts
index ee0bedd3f27..6d402797bab 100644
--- a/src/codex/quota.ts
+++ b/src/codex/quota.ts
@@ -11,15 +11,23 @@ export type WhamUsageResponse = {
   email?: string | null;
   plan_type?: string | null;
   rate_limit?: {
-    primary_window?: { used_percent?: number; reset_at?: number };
-    secondary_window?: { used_percent?: number; reset_at?: number };
-    tertiary_window?: { used_percent?: number; reset_at?: number };
+    primary_window?: WhamUsageWindow;
+    secondary_window?: WhamUsageWindow;
+    tertiary_window?: WhamUsageWindow;
   };
   rate_limit_reset_credits?: {
     available_count: number;
   } | null;
 };
 
+type WhamUsageWindow = {
+  used_percent?: number;
+  reset_at?: number;
+  limit_window_seconds?: number;
+};
+
+const MONTHLY_WINDOW_MIN_SECONDS = 28 * 24 * 60 * 60;
+
 const accountQuota = new Map<string, StoredAccountQuota>();
 
 export const CODEX_UNKNOWN_USAGE_SCORE = 100;
@@ -49,6 +57,13 @@ function hasKnownQuotaValue(quota: Omit<StoredAccountQuota, "updatedAt">): boole
     .some(value => typeof value === "number" && Number.isFinite(value));
 }
 
+function isExplicitMonthlyWindow(window: WhamUsageWindow | undefined): boolean {
+  const seconds = window?.limit_window_seconds;
+  return typeof seconds === "number"
+    && Number.isFinite(seconds)
+    && seconds >= MONTHLY_WINDOW_MIN_SECONDS;
+}
+
 export function updateAccountQuota(
   accountId: string,
   weekly: unknown,
@@ -110,16 +125,30 @@ export function parseUsageQuota(data: WhamUsageResponse): Omit<StoredAccountQuot
 
   const quota: Omit<StoredAccountQuota, "updatedAt"> = {};
   const thirtyDayOnly = data.plan_type?.trim().toLowerCase() === "go" || data.plan_type?.trim().toLowerCase() === "free";
-  // primary_window was the 5h window; it now carries weekly data for GPT plans.
-  // secondary_window is the legacy weekly source; prefer primary when present.
-  const primaryPercent = normalizeUsagePercent(data.rate_limit.primary_window?.used_percent);
-  const secondaryPercent = normalizeUsagePercent(data.rate_limit.secondary_window?.used_percent);
-  const weeklyPercent = primaryPercent ?? secondaryPercent;
-  const monthlyPercent = normalizeUsagePercent(data.rate_limit.tertiary_window?.used_percent);
-  const primaryResetAt = normalizeResetAt(data.rate_limit.primary_window?.reset_at);
-  const secondaryResetAt = normalizeResetAt(data.rate_limit.secondary_window?.reset_at);
-  const weeklyResetAt = primaryPercent !== undefined ? primaryResetAt : secondaryResetAt;
-  const monthlyResetAt = normalizeResetAt(data.rate_limit.tertiary_window?.reset_at);
+  const primaryWindow = data.rate_limit.primary_window;
+  const secondaryWindow = data.rate_limit.secondary_window;
+  const tertiaryWindow = data.rate_limit.tertiary_window;
+  const primaryPercent = normalizeUsagePercent(primaryWindow?.used_percent);
+  const secondaryPercent = normalizeUsagePercent(secondaryWindow?.used_percent);
+  const tertiaryPercent = normalizeUsagePercent(tertiaryWindow?.used_percent);
+  const primaryResetAt = normalizeResetAt(primaryWindow?.reset_at);
+  const secondaryResetAt = normalizeResetAt(secondaryWindow?.reset_at);
+  const tertiaryResetAt = normalizeResetAt(tertiaryWindow?.reset_at);
+  const primaryIsMonthly = isExplicitMonthlyWindow(primaryWindow);
+
+  // [Decision Log]
+  // - 목적과 의도: distinguish weekly and roughly monthly WHAM primary windows without plan-name guesses.
+  // - 기존 구현 및 제약 조건: primary meant weekly, and older responses omit limit_window_seconds.
+  // - 검토한 주요 대안: exact-duration matching, plan-specific mapping, and a duration lower bound.
+  // - 선택한 방식: only an explicit primary duration of at least 28 days changes it to monthly.
+  // - 다른 대안 대신 이 방식을 선택한 이유: it accepts calendar-month variance and preserves legacy payloads.
+  // - 장점, 단점 및 영향: Team monthly quotas classify correctly; unknown durations remain weekly by design.
+  const weeklyPercent = primaryIsMonthly ? secondaryPercent : primaryPercent ?? secondaryPercent;
+  const weeklyResetAt = primaryIsMonthly
+    ? secondaryResetAt
+    : primaryPercent !== undefined ? primaryResetAt : secondaryResetAt;
+  const monthlyPercent = primaryIsMonthly ? primaryPercent ?? tertiaryPercent : tertiaryPercent;
+  const monthlyResetAt = primaryIsMonthly && primaryPercent !== undefined ? primaryResetAt : tertiaryResetAt;
   if (thirtyDayOnly) {
     if (monthlyPercent !== undefined) {
       quota.monthlyPercent = monthlyPercent;
diff --git a/tests/codex-routing.test.ts b/tests/codex-routing.test.ts
index a7994d5f598..c8deffbf675 100644
--- a/tests/codex-routing.test.ts
+++ b/tests/codex-routing.test.ts
@@ -571,6 +571,46 @@ describe("codex routing", () => {
     });
   });
 
+  test("WHAM primary window uses its explicit duration to distinguish weekly and monthly quotas", () => {
+    expect(parseUsageQuota({
+      plan_type: "team",
+      rate_limit: {
+        primary_window: { used_percent: 20, reset_at: 2, limit_window_seconds: 604_800 },
+      },
+    })).toEqual({ weeklyPercent: 20, weeklyResetAt: 2 });
+
+    expect(parseUsageQuota({
+      plan_type: "team",
+      rate_limit: {
+        primary_window: { used_percent: 39, reset_at: 3, limit_window_seconds: 2_628_000 },
+      },
+    })).toEqual({ monthlyPercent: 39, monthlyResetAt: 3 });
+  });
+
+  test("WHAM monthly primary preserves a legacy secondary weekly window", () => {
+    expect(parseUsageQuota({
+      plan_type: "team",
+      rate_limit: {
+        primary_window: { used_percent: 39, reset_at: 30, limit_window_seconds: 2_628_000 },
+        secondary_window: { used_percent: 12, reset_at: 7, limit_window_seconds: 604_800 },
+      },
+    })).toEqual({
+      weeklyPercent: 12,
+      weeklyResetAt: 7,
+      monthlyPercent: 39,
+      monthlyResetAt: 30,
+    });
+  });
+
+  test("WHAM primary window without duration keeps the legacy weekly fallback", () => {
+    expect(parseUsageQuota({
+      plan_type: "team",
+      rate_limit: {
+        primary_window: { used_percent: 6, reset_at: 7 },
+      },
+    })).toEqual({ weeklyPercent: 6, weeklyResetAt: 7 });
+  });
+
   test("WHAM parser returns null when no valid quota window is present", () => {
     expect(parseUsageQuota({ rate_limit: {} })).toBeNull();
     expect(parseUsageQuota({