diff --git a/packages/ai/src/usage/xai-oauth.ts b/packages/ai/src/usage/xai-oauth.ts
index 161533d1f..b15984491 100644
--- a/packages/ai/src/usage/xai-oauth.ts
+++ b/packages/ai/src/usage/xai-oauth.ts
@@ -202,9 +202,12 @@ function parseMonthlyBillingConfig(raw: Record<string, unknown>): XaiMonthlyBill
 		onDemandUsed: parseOnDemandAmount(raw.onDemandUsed),
 	};
 }
-function hasPositiveMonthlyLimit(raw: Record<string, unknown>): boolean {
+
+function confirmsNoMonthlyQuota(raw: Record<string, unknown>): boolean {
 	const limit = parseOnDemandAmount(raw.monthlyLimit);
-	return limit !== undefined && limit > 0;
+	if (limit !== undefined) return limit === 0;
+	// Some weekly accounts return the credits shape from the default endpoint too.
+	return parseWeeklyBillingConfig(raw)?.inferredPercent === true;
 }
 
 function buildOnDemandLimit(
@@ -393,7 +396,7 @@ export const xaiOauthUsageProvider: UsageProvider = {
 					monthlyPayload && isRecord(monthlyPayload) && isRecord(monthlyPayload.config)
 						? monthlyPayload.config
 						: null;
-				if (!monthlyConfig || hasPositiveMonthlyLimit(monthlyConfig)) {
+				if (!monthlyConfig || !confirmsNoMonthlyQuota(monthlyConfig)) {
 					effectiveWeekly = null;
 				}
 			}
diff --git a/packages/ai/test/xai-oauth-usage.test.ts b/packages/ai/test/xai-oauth-usage.test.ts
index 09674d4ff..e2556ef80 100644
--- a/packages/ai/test/xai-oauth-usage.test.ts
+++ b/packages/ai/test/xai-oauth-usage.test.ts
@@ -336,6 +336,31 @@ describe("xai-oauth usage provider", () => {
 		expect(report).toBeNull();
 	});
 
+	it("rejects inferred unified weekly usage when monthly quota evidence is absent", async () => {
+		const periodEnd = new Date(Date.now() + 6 * 24 * 60 * 60 * 1000).toISOString();
+		const periodStart = new Date(Date.now() - 24 * 60 * 60 * 1000).toISOString();
+		const report = await xaiOauthUsageProvider.fetchUsage(
+			{ provider: "xai-oauth", credential: makeCredential() },
+			{
+				fetch: dualBillingFetch(
+					{
+						config: {
+							currentPeriod: {
+								end: periodEnd,
+								start: periodStart,
+								type: "USAGE_PERIOD_TYPE_WEEKLY",
+							},
+							isUnifiedBillingUser: true,
+						},
+					},
+					{ config: { isUnifiedBillingUser: true } },
+				).fetch,
+			},
+		);
+
+		expect(report).toBeNull();
+	});
+
 	it("falls back to monthly included quota when credits has no percent fields", async () => {
 		const { fetch, calls } = dualBillingFetch(makeUnifiedCreditsPayload(), makeUnifiedMonthlyPayload());
 		const report = await xaiOauthUsageProvider.fetchUsage(