diff --git a/packages/ai/src/model-thinking.ts b/packages/ai/src/model-thinking.ts
index 4710b863d..d39bff11a 100644
--- a/packages/ai/src/model-thinking.ts
+++ b/packages/ai/src/model-thinking.ts
@@ -182,8 +182,11 @@ export function linkOpenAIPromotionTargets(models: ApiModel<Api>[]): void {
 }
 
 /**
- * Returns supported thinking efforts from canonical model rules constrained by
- * explicit model metadata.
+ * Returns the supported thinking efforts declared on the model metadata.
+ *
+ * Catalog enrichment is responsible for normalizing bundled model metadata up front.
+ * Runtime callers must treat explicit `model.thinking` on custom models as authoritative
+ * so proxy-specific overrides from `models.yml` survive request construction.
  *
  * @throws Error when a reasoning-capable model is missing thinking metadata
  */
@@ -194,12 +197,7 @@ export function getSupportedEfforts<TApi extends Api>(model: ApiModel<TApi>): re
 	if (!model.thinking) {
 		throw new Error(`Model ${model.provider}/${model.id} is missing thinking metadata`);
 	}
-	const configuredEfforts = expandEffortRange(model.thinking);
-	const parsedModel = parseKnownModel(model.id);
-	if (parsedModel.family === "unknown") {
-		return configuredEfforts;
-	}
-	return intersectEfforts(configuredEfforts, inferSupportedEfforts(parsedModel, model));
+	return expandEffortRange(model.thinking);
 }
 
 /**
@@ -421,10 +419,6 @@ function expandEffortRange(thinking: ThinkingConfig): readonly Effort[] {
 	return THINKING_EFFORTS.slice(minIndex, maxIndex + 1);
 }
 
-function intersectEfforts(left: readonly Effort[], right: readonly Effort[]): readonly Effort[] {
-	return left.filter(effort => right.includes(effort));
-}
-
 function inferSupportedEfforts<TApi extends Api>(parsedModel: ParsedModel, model: ApiModel<TApi>): readonly Effort[] {
 	switch (parsedModel.family) {
 		case "openai":
diff --git a/packages/ai/test/issue-969-repro.test.ts b/packages/ai/test/issue-969-repro.test.ts
new file mode 100644
index 000000000..1b347470e
--- /dev/null
+++ b/packages/ai/test/issue-969-repro.test.ts
@@ -0,0 +1,81 @@
+import { afterEach, describe, expect, it } from "bun:test";
+import { Effort, getSupportedEfforts } from "../src/model-thinking";
+import { streamOpenAICompletions } from "../src/providers/openai-completions";
+import type { Context, Model } from "../src/types";
+
+const originalFetch = global.fetch;
+
+afterEach(() => {
+	global.fetch = originalFetch;
+});
+
+const testContext: Context = {
+	messages: [{ role: "user", content: "hello", timestamp: 0 }],
+};
+
+function createSseResponse(events: unknown[]): Response {
+	const payload = `${events.map(event => `data: ${typeof event === "string" ? event : JSON.stringify(event)}`).join("\n\n")}\n\n`;
+	return new Response(payload, {
+		status: 200,
+		headers: { "content-type": "text/event-stream" },
+	});
+}
+
+function customOpenAICompatModel(): Model<"openai-completions"> {
+	return {
+		id: "gpt-5.1",
+		name: "GPT-5.1 proxy",
+		api: "openai-completions",
+		provider: "custom",
+		baseUrl: "https://proxy.example.com/v1",
+		reasoning: true,
+		thinking: {
+			mode: "effort",
+			minLevel: Effort.Low,
+			maxLevel: Effort.XHigh,
+		},
+		input: ["text"],
+		cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+		contextWindow: 128_000,
+		maxTokens: 16_384,
+	};
+}
+
+describe("issue #969 — custom thinking metadata must preserve explicit xhigh", () => {
+	it("uses the configured xhigh effort for custom OpenAI-compatible models", async () => {
+		const model = customOpenAICompatModel();
+		let payload: Record<string, unknown> | undefined;
+		global.fetch = Object.assign(
+			async (_input: string | URL | Request, init?: RequestInit): Promise<Response> => {
+				payload = JSON.parse(typeof init?.body === "string" ? init.body : "{}") as Record<string, unknown>;
+				return createSseResponse([
+					{
+						id: "chatcmpl-969",
+						object: "chat.completion.chunk",
+						created: 0,
+						model: model.id,
+						choices: [{ index: 0, delta: { content: "ok" } }],
+					},
+					{
+						id: "chatcmpl-969",
+						object: "chat.completion.chunk",
+						created: 0,
+						model: model.id,
+						choices: [{ index: 0, delta: {}, finish_reason: "stop" }],
+					},
+					"[DONE]",
+				]);
+			},
+			{ preconnect: originalFetch.preconnect },
+		);
+
+		expect(getSupportedEfforts(model)).toContain(Effort.XHigh);
+		const result = await streamOpenAICompletions(model, testContext, {
+			apiKey: "test-key",
+			reasoning: "xhigh",
+		}).result();
+
+		expect(result.stopReason).toBe("stop");
+		expect(payload?.reasoning_effort).toBe("xhigh");
+	});
+});