diff --git a/packages/ai/src/usage/xai-oauth.ts b/packages/ai/src/usage/xai-oauth.ts
index 63bb8006f..161533d1f 100644
--- a/packages/ai/src/usage/xai-oauth.ts
+++ b/packages/ai/src/usage/xai-oauth.ts
@@ -202,6 +202,10 @@ function parseMonthlyBillingConfig(raw: Record<string, unknown>): XaiMonthlyBill
 		onDemandUsed: parseOnDemandAmount(raw.onDemandUsed),
 	};
 }
+function hasPositiveMonthlyLimit(raw: Record<string, unknown>): boolean {
+	const limit = parseOnDemandAmount(raw.monthlyLimit);
+	return limit !== undefined && limit > 0;
+}
 
 function buildOnDemandLimit(
 	onDemandCap: number | undefined,
@@ -384,8 +388,14 @@ export const xaiOauthUsageProvider: UsageProvider = {
 		if (weekly?.inferredPercent && creditsLooksUnified) {
 			if (monthly) {
 				effectiveWeekly = null;
-			} else if (!monthlyPayload || !isRecord(monthlyPayload) || !isRecord(monthlyPayload.config)) {
-				effectiveWeekly = null;
+			} else {
+				const monthlyConfig =
+					monthlyPayload && isRecord(monthlyPayload) && isRecord(monthlyPayload.config)
+						? monthlyPayload.config
+						: null;
+				if (!monthlyConfig || hasPositiveMonthlyLimit(monthlyConfig)) {
+					effectiveWeekly = null;
+				}
 			}
 		}
 		if (!effectiveWeekly && !monthly) return null;
diff --git a/packages/ai/test/xai-oauth-usage.test.ts b/packages/ai/test/xai-oauth-usage.test.ts
index 30cc1539b..09674d4ff 100644
--- a/packages/ai/test/xai-oauth-usage.test.ts
+++ b/packages/ai/test/xai-oauth-usage.test.ts
@@ -305,6 +305,36 @@ describe("xai-oauth usage provider", () => {
 
 		expect(report).toBeNull();
 	});
+	it("rejects inferred unified weekly usage when monthly config has a positive limit but malformed fields", 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,
+							monthlyLimit: { val: 15000 },
+							// Missing 'used' and billingPeriod dates
+						},
+					},
+				).fetch,
+			},
+		);
+
+		expect(report).toBeNull();
+	});
 
 	it("falls back to monthly included quota when credits has no percent fields", async () => {
 		const { fetch, calls } = dualBillingFetch(makeUnifiedCreditsPayload(), makeUnifiedMonthlyPayload());