diff --git a/src/agent/models.ts b/src/agent/models.ts
index 001f5c1..69815cf 100644
--- a/src/agent/models.ts
+++ b/src/agent/models.ts
@@ -43,8 +43,8 @@ export const APP_IDENTITY = Object.freeze({
 export interface PiEngine {
 	model: Model<Api>;
 	streamFn: StreamFunction;
-	/** The resolved (config-or-settings, CLAMPED) thinking level —
-	 *  observability + tests; the streamFn pins it anyway. */
+	/** The initially resolved (config-or-settings, CLAMPED) thinking level.
+	 *  Custom streams re-resolve the original preference per operation. */
 	level?: ThinkingLevel;
 }
 
@@ -128,8 +128,9 @@ export function piEngineForSpec(spec: ResolvedModelSpec, background: boolean | (
 	// UNSET level → the baked default order (first entry the model
 	// supports); SET level → pi's native nearest-clamp (model swaps keep
 	// the user's intent and adapt honestly).
-	const level = spec.thinkingLevel
-		? clampThinkingLevel(model, spec.thinkingLevel)
+	const thinkingPreference = spec.thinkingLevel;
+	const level = thinkingPreference
+		? clampThinkingLevel(model, thinkingPreference)
 		: defaultThinkingLevel(model);
 	// A lesson's agent loop can stay alive through many tool calls. Remember
 	// only that this is a custom route, never its configuration for that run.
@@ -137,21 +138,24 @@ export function piEngineForSpec(spec: ResolvedModelSpec, background: boolean | (
 	return {
 		model,
 		level,
-		// bound streamSimple: the agent loop forwards state.thinkingLevel as
-		// `reasoning` (undefined = off on pi-ai's scale); the clamp above keeps
-		// the pin honest even when config or settings drift off the map.
+		// The agent loop forwards state.thinkingLevel as `reasoning` (undefined
+		// = off on pi-ai's scale). Built-ins keep the factory clamp; custom
+		// requests re-resolve thinking against their current metadata below.
 		streamFn: (requestModel, context, options) => {
-			const requestOptions = { ...options, reasoning: level === "off" ? undefined : level };
 			if (custom) {
 				// Revalidate before EVERY upstream model operation, including later
-				// tool-loop steps. Pi resolves auth and clamps the requested thinking
-				// against the current native model. Its in-flight operation retains
-				// its own setup; a subsequent operation uses the reloaded provider.
+				// tool-loop steps. Resolve thinking from the ORIGINAL preference (or
+				// existing default order), not a previous metadata snapshot's clamp.
+				// Pi retains the setup of an operation already in flight.
 				const current = piModels();
 				const currentModel = current.getModel(spec.provider, spec.id);
 				if (!currentModel) return lazyStream(requestModel, async () => { throw new Error("The selected custom model is unavailable."); });
-				return current.streamSimple(currentModel, context, requestOptions);
+				const currentLevel = thinkingPreference
+					? clampThinkingLevel(currentModel, thinkingPreference)
+					: defaultThinkingLevel(currentModel);
+				return current.streamSimple(currentModel, context, { ...options, reasoning: currentLevel === "off" ? undefined : currentLevel });
 			}
+			const requestOptions = { ...options, reasoning: level === "off" ? undefined : level };
 			const purpose = typeof background === "function" ? background : () => background;
 			const stream = spec.provider === "chatgpt" ? chatGPTStream(purpose, lifecycle) : nativeId ? nativeSubscriptionStream(models.getProvider(nativeId)!, purpose, lifecycle) : models.streamSimple.bind(models);
 			return stream(requestModel, context, requestOptions);
diff --git a/tests/custom-providers.test.ts b/tests/custom-providers.test.ts
index 2cdd415..71e9aa3 100644
--- a/tests/custom-providers.test.ts
+++ b/tests/custom-providers.test.ts
@@ -3,7 +3,8 @@ import { after, describe, it } from "node:test";
 import fs from "node:fs";
 import os from "node:os";
 import path from "node:path";
-import { createModels, normalizeContext } from "@earendil-works/pi-ai";
+import { createModels, normalizeContext, type SimpleStreamOptions } from "@earendil-works/pi-ai";
+import type { ThinkingLevel } from "@earendil-works/pi-agent-core";
 import { parseCustomProviders, resolveCustomValue } from "../src/core/custom-providers.ts";
 import { createCustomProvider, customProviderApis } from "../src/agent/custom-providers.ts";
 
@@ -187,6 +188,46 @@ describe("custom providers in the existing application wiring", () => {
 		assert.equal(requests[0]!.body.max_tokens, 1024);
 		assert.equal(requests[1]!.body.max_tokens, 512, "current Pi model metadata, not the stale engine model, controls the request");
 	});
+	const thinking = (...levels: ThinkingLevel[]) => ({
+		reasoning: true,
+		// Pi treats omitted levels through high as supported; mark every
+		// unselected level explicitly unsupported for these narrow fixtures.
+		thinkingLevelMap: { off: null, minimal: null, low: null, medium: null, high: null, xhigh: null, max: null, ...Object.fromEntries(levels.map((level) => [level, level])) },
+	});
+	const thinkingCases: { name: string; preference?: ThinkingLevel; initial: object; updated: object; before: ThinkingLevel; after: ThinkingLevel }[] = [
+		{ name: "recovers saved max after high-only metadata expands", preference: "max", initial: thinking("high"), updated: thinking("high", "max"), before: "high", after: "max" },
+		{ name: "recovers saved max after reasoning-off metadata expands", preference: "max", initial: { reasoning: false }, updated: thinking("high", "max"), before: "off", after: "max" },
+		{ name: "selects the existing medium-first default after reasoning becomes supported", initial: { reasoning: false }, updated: thinking("low", "medium", "high"), before: "off", after: "medium" },
+		{ name: "reselects the existing low-before-high default against updated metadata", initial: thinking("high"), updated: thinking("low", "high"), before: "high", after: "low" },
+		{ name: "clamps saved max when supported thinking contracts", preference: "max", initial: thinking("high", "max"), updated: thinking("high"), before: "max", after: "high" },
+		{ name: "omits reasoning when the model loses thinking support", preference: "max", initial: thinking("high", "max"), updated: { reasoning: false }, before: "max", after: "off" },
+	];
+	for (const scenario of thinkingCases) it(scenario.name, async () => {
+		const definition = (metadata: object) => config({ compat: { supportsReasoningEffort: true, thinkingFormat: "openai" } }, [model("chat", metadata)]);
+		save(definition(scenario.initial));
+		const engine = piEngineForSpec({ provider: "gateway", id: "chat", thinkingLevel: scenario.preference });
+		assert.equal(engine.level, scenario.before);
+		const requests: Record<string, unknown>[] = [];
+		const original = globalThis.fetch;
+		globalThis.fetch = async (input, init) => {
+			const request = input instanceof Request ? input : new Request(input, init);
+			requests.push(await request.json() as Record<string, unknown>);
+			return sseText();
+		};
+		try {
+			const context = normalizeContext({ messages: [{ role: "user", content: "hello", timestamp: 1 }] });
+			// A long-lived agent still forwards its initial thinking setting.
+			const options: SimpleStreamOptions = { reasoning: engine.level === "off" ? undefined : engine.level };
+			assert.equal((await engine.streamFn(engine.model, context, options).result()).stopReason, "stop");
+			save(definition(scenario.updated));
+			assert.equal((await engine.streamFn(engine.model, context, options).result()).stopReason, "stop");
+		} finally { globalThis.fetch = original; }
+		assert.equal(requests.length, 2);
+		for (const [index, level] of [scenario.before, scenario.after].entries()) {
+			assert.equal(requests[index]!.reasoning_effort, level === "off" ? undefined : level);
+			if (level === "off") assert.equal("reasoning_effort" in requests[index]!, false);
+		}
+	});
 	it("disables custom routes on malformed edits without removing built-ins or saved choices", () => {
 		fs.writeFileSync(SETTINGS_FILE, JSON.stringify({ version: 1, models: { strong: { model: { provider: "gateway", id: "chat" }, thinkingLevel: "high" } } }));
 		const before = fs.readFileSync(SETTINGS_FILE, "utf8");