feat(ai): add Claude Fable 5 metadata

packages/ai/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added Claude Fable 5 to Anthropic and Amazon Bedrock model metadata, with adaptive thinking and `xhigh` effort support.
+
 ### Fixed
 
 - Fixed Amazon Bedrock inference profile ARN region resolution to prefer the ARN's embedded region over `AWS_REGION` ([#5527](https://github.com/earendil-works/pi/pull/5527) by [@AJM10565](https://github.com/AJM10565)).

packages/ai/scripts/generate-models.ts

@@ -232,7 +232,8 @@ function isAnthropicAdaptiveThinkingModel(modelId: string): boolean {
 		modelId.includes("opus-4-8") ||
 		modelId.includes("opus-4.8") ||
 		modelId.includes("sonnet-4-6") ||
-		modelId.includes("sonnet-4.6")
+		modelId.includes("sonnet-4.6") ||
+		modelId.includes("fable-5")
 	);
 }
 
@@ -294,6 +295,12 @@ function applyThinkingLevelMetadata(model: Model<any>): void {
 	) {
 		mergeThinkingLevelMap(model, { xhigh: "xhigh" });
 	}
+	if (
+		(model.api === "anthropic-messages" || model.api === "bedrock-converse-stream") &&
+		model.id.includes("fable-5")
+	) {
+		mergeThinkingLevelMap(model, { xhigh: "xhigh" });
+	}
 	if (model.api === "anthropic-messages" && isAnthropicAdaptiveThinkingModel(model.id)) {
 		mergeAnthropicMessagesCompat(model, { forceAdaptiveThinking: true });
 	}

packages/ai/src/providers/amazon-bedrock.ts

@@ -528,13 +528,18 @@ function getModelMatchCandidates(modelId: string, modelName?: string): string[]
 function supportsAdaptiveThinking(modelId: string, modelName?: string): boolean {
 	const candidates = getModelMatchCandidates(modelId, modelName);
 	return candidates.some(
-		(s) => s.includes("opus-4-6") || s.includes("opus-4-7") || s.includes("opus-4-8") || s.includes("sonnet-4-6"),
+		(s) =>
+			s.includes("opus-4-6") ||
+			s.includes("opus-4-7") ||
+			s.includes("opus-4-8") ||
+			s.includes("sonnet-4-6") ||
+			s.includes("fable-5"),
 	);
 }
 
 function supportsNativeXhighEffort(model: Model<"bedrock-converse-stream">): boolean {
 	const candidates = getModelMatchCandidates(model.id, model.name);
-	return candidates.some((s) => s.includes("opus-4-7") || s.includes("opus-4-8"));
+	return candidates.some((s) => s.includes("opus-4-7") || s.includes("opus-4-8") || s.includes("fable-5"));
 }
 
 function mapThinkingLevelToEffort(

packages/ai/src/providers/anthropic.ts

@@ -200,7 +200,7 @@ export interface AnthropicOptions extends StreamOptions {
 	 * Effort level for adaptive thinking models.
 	 * Controls how much thinking Claude allocates:
 	 * - "max": Always thinks with no constraints (Opus 4.6 only)
-	 * - "xhigh": Highest reasoning level (Opus 4.7)
+	 * - "xhigh": Highest reasoning level (Opus 4.7+, Fable 5)
 	 * - "high": Always thinks, deep reasoning
 	 * - "medium": Moderate thinking, may skip for simple queries
 	 * - "low": Minimal thinking, skips for simple tasks
@@ -711,7 +711,7 @@ export const streamAnthropic: StreamFunction<"anthropic-messages", AnthropicOpti
 
 /**
  * Map ThinkingLevel to Anthropic effort levels for adaptive thinking.
- * Note: effort "max" is only valid on Opus 4.6, while Opus 4.7 supports "xhigh".
+ * Note: effort "max" is only valid on Opus 4.6, while Opus 4.7+ and Fable 5 support "xhigh".
  */
 function mapThinkingLevelToEffort(
 	model: Model<"anthropic-messages">,

packages/ai/test/anthropic-force-adaptive-thinking.test.ts

@@ -83,6 +83,13 @@ describe("Anthropic forceAdaptiveThinking compat override", () => {
 		expect(payload.output_config).toEqual({ effort: "medium" });
 	});
 
+	it("uses adaptive thinking with native xhigh effort for Claude Fable 5", async () => {
+		const payload = await capturePayload(getModel("anthropic", "claude-fable-5"), { reasoning: "xhigh" });
+
+		expect(payload.thinking).toEqual({ type: "adaptive", display: "summarized" });
+		expect(payload.output_config).toEqual({ effort: "xhigh" });
+	});
+
 	it("allows built-in adaptive models to opt out with compat.forceAdaptiveThinking false", async () => {
 		const model: Model<"anthropic-messages"> = {
 			...getModel("anthropic", "claude-opus-4-8"),

packages/ai/test/bedrock-thinking-payload.test.ts

@@ -83,6 +83,25 @@ describe("Bedrock thinking payload", () => {
 		expect(payload.additionalModelRequestFields?.anthropic_beta).toBeUndefined();
 	});
 
+	it("uses adaptive thinking for Claude Fable 5 when reasoning is enabled", async () => {
+		const model = getModel("amazon-bedrock", "global.anthropic.claude-fable-5");
+
+		const payload = await capturePayload(model);
+
+		expect(payload.additionalModelRequestFields?.thinking).toEqual({ type: "adaptive", display: "summarized" });
+		expect(payload.additionalModelRequestFields?.output_config).toEqual({ effort: "high" });
+		expect(payload.additionalModelRequestFields?.anthropic_beta).toBeUndefined();
+	});
+
+	it("maps xhigh reasoning to effort=xhigh for Claude Fable 5", async () => {
+		const model = getModel("amazon-bedrock", "global.anthropic.claude-fable-5");
+
+		const payload = await capturePayload(model, { reasoning: "xhigh" });
+
+		expect(payload.additionalModelRequestFields?.thinking).toEqual({ type: "adaptive", display: "summarized" });
+		expect(payload.additionalModelRequestFields?.output_config).toEqual({ effort: "xhigh" });
+	});
+
 	it("omits display for GovCloud model ids on non-adaptive Claude thinking", async () => {
 		const baseModel = getModel("amazon-bedrock", "us.anthropic.claude-sonnet-4-5-20250929-v1:0");
 		const model: Model<"bedrock-converse-stream"> = {

packages/ai/test/supports-xhigh.test.ts

@@ -20,7 +20,13 @@ describe("getSupportedThinkingLevels", () => {
 		expect(getSupportedThinkingLevels(model!)).toContain("xhigh");
 	});
 
-	it("does not include xhigh for non-Opus Anthropic models", () => {
+	it("includes xhigh for Anthropic Claude Fable 5 on anthropic-messages API", () => {
+		const model = getModel("anthropic", "claude-fable-5");
+		expect(model).toBeDefined();
+		expect(getSupportedThinkingLevels(model!)).toContain("xhigh");
+	});
+
+	it("does not include xhigh for Claude Sonnet 4.5", () => {
 		const model = getModel("anthropic", "claude-sonnet-4-5");
 		expect(model).toBeDefined();
 		expect(getSupportedThinkingLevels(model!)).not.toContain("xhigh");
@@ -79,4 +85,10 @@ describe("getSupportedThinkingLevels", () => {
 		expect(model).toBeDefined();
 		expect(getSupportedThinkingLevels(model!)).toContain("xhigh");
 	});
+
+	it("includes xhigh for Bedrock Claude Fable 5", () => {
+		const model = getModel("amazon-bedrock", "global.anthropic.claude-fable-5");
+		expect(model).toBeDefined();
+		expect(getSupportedThinkingLevels(model!)).toContain("xhigh");
+	});
 });