diff --git a/packages/pi-ai/src/index.ts b/packages/pi-ai/src/index.ts
index 8b81cc22e..b645e2e32 100644
--- a/packages/pi-ai/src/index.ts
+++ b/packages/pi-ai/src/index.ts
@@ -5,6 +5,10 @@ export * from "./api-registry.js";
 export * from "./env-api-keys.js";
 export * from "./models.js";
 export * from "./providers/anthropic.js";
+export {
+	mapThinkingLevelToEffort,
+	supportsAdaptiveThinking,
+} from "./providers/anthropic-shared.js";
 export * from "./providers/azure-openai-responses.js";
 export * from "./providers/google.js";
 export * from "./providers/google-gemini-cli.js";
diff --git a/src/resources/extensions/claude-code-cli/stream-adapter.ts b/src/resources/extensions/claude-code-cli/stream-adapter.ts
index d8d3e35f5..d3b9f5f77 100644
--- a/src/resources/extensions/claude-code-cli/stream-adapter.ts
+++ b/src/resources/extensions/claude-code-cli/stream-adapter.ts
@@ -14,10 +14,11 @@ import type {
 	Context,
 	Model,
 	SimpleStreamOptions,
+	ThinkingLevel,
 	ToolCall,
 } from "@gsd/pi-ai";
 import type { ExtensionUIContext } from "@gsd/pi-coding-agent";
-import { EventStream } from "@gsd/pi-ai";
+import { EventStream, mapThinkingLevelToEffort, supportsAdaptiveThinking } from "@gsd/pi-ai";
 import { execSync } from "node:child_process";
 import { PartialMessageBuilder, ZERO_USAGE, mapUsage } from "./partial-builder.js";
 import { buildWorkflowMcpServers } from "../gsd/workflow-mcp.js";
@@ -600,8 +601,9 @@ export function buildSdkOptions(
 	modelId: string,
 	prompt: string,
 	overrides?: { permissionMode?: "bypassPermissions" | "acceptEdits" | "default" | "plan" },
-	extraOptions: Record<string, unknown> = {},
+	extraOptions: Record<string, unknown> & { reasoning?: ThinkingLevel } = {},
 ): Record<string, unknown> {
+	const { reasoning, ...sdkExtraOptions } = extraOptions;
 	const mcpServers = buildWorkflowMcpServers();
 	const permissionMode = overrides?.permissionMode ?? "bypassPermissions";
 	const disallowedTools = ["AskUserQuestion"];
@@ -620,6 +622,10 @@ export function buildSdkOptions(
 		"Bash(pwd)",
 		...(mcpServers ? Object.keys(mcpServers).map((serverName) => `mcp__${serverName}__*`) : []),
 	];
+	const effort =
+		reasoning && supportsAdaptiveThinking(modelId)
+			? mapThinkingLevelToEffort(reasoning, modelId)
+			: undefined;
 	return {
 		pathToClaudeCodeExecutable: getClaudePath(),
 		model: modelId,
@@ -634,7 +640,8 @@ export function buildSdkOptions(
 		...(allowedTools.length > 0 ? { allowedTools } : {}),
 		...(mcpServers ? { mcpServers } : {}),
 		betas: modelId.includes("sonnet") ? ["context-1m-2025-08-07"] : [],
-		...extraOptions,
+		...(effort ? { effort } : {}),
+		...sdkExtraOptions,
 	};
 }
 
@@ -828,11 +835,12 @@ async function pumpSdkMessages(
 			{ permissionMode },
 			typeof (options as ClaudeCodeStreamOptions | undefined)?.extensionUIContext === "object"
 				? {
+						reasoning: options?.reasoning,
 						onElicitation: createClaudeCodeElicitationHandler(
 							(options as ClaudeCodeStreamOptions | undefined)?.extensionUIContext,
 						),
 					}
-				: {},
+				: { reasoning: options?.reasoning },
 		);
 
 		const queryResult = sdk.query({
diff --git a/src/resources/extensions/claude-code-cli/tests/stream-adapter.test.ts b/src/resources/extensions/claude-code-cli/tests/stream-adapter.test.ts
index a600852a4..29b3003f3 100644
--- a/src/resources/extensions/claude-code-cli/tests/stream-adapter.test.ts
+++ b/src/resources/extensions/claude-code-cli/tests/stream-adapter.test.ts
@@ -343,6 +343,26 @@ describe("stream-adapter — session persistence (#2859)", () => {
 		);
 	});
 
+	test("buildSdkOptions maps reasoning to effort for adaptive Claude Code models (#3917)", () => {
+		const options = buildSdkOptions("claude-sonnet-4-6", "test", undefined, { reasoning: "high" });
+		assert.equal(options.effort, "high");
+	});
+
+	test("buildSdkOptions upgrades xhigh reasoning to max for opus 4.6 (#3917)", () => {
+		const options = buildSdkOptions("claude-opus-4-6", "test", undefined, { reasoning: "xhigh" });
+		assert.equal(options.effort, "max");
+	});
+
+	test("buildSdkOptions omits effort when reasoning is undefined (#3917)", () => {
+		const options = buildSdkOptions("claude-sonnet-4-6", "test");
+		assert.equal("effort" in options, false);
+	});
+
+	test("buildSdkOptions omits effort for non-adaptive Claude models (#3917)", () => {
+		const options = buildSdkOptions("claude-sonnet-4-20250514", "test", undefined, { reasoning: "high" });
+		assert.equal("effort" in options, false);
+	});
+
 	test("buildSdkOptions includes workflow MCP server config when env is set", () => {
 		const prev = {
 			GSD_WORKFLOW_MCP_COMMAND: process.env.GSD_WORKFLOW_MCP_COMMAND,
@@ -774,11 +794,12 @@ describe("stream-adapter — MCP elicitation bridge", () => {
 			},
 		};
 
+		const secureValue = "ui-collected-value";
 		const inputCalls: Array<{ opts?: { secure?: boolean } }> = [];
 		const handler = createClaudeCodeElicitationHandler({
 			input: async (_title: string, _placeholder?: string, opts?: { secure?: boolean }) => {
 				inputCalls.push({ opts });
-				return "example-secure-input";
+				return secureValue;
 			},
 		} as any);
 		assert.ok(handler);
@@ -787,7 +808,7 @@ describe("stream-adapter — MCP elicitation bridge", () => {
 		assert.deepEqual(result, {
 			action: "accept",
 			content: {
-				TEST_SECURE_FIELD: "example-secure-input",
+				TEST_SECURE_FIELD: secureValue,
 			},
 		});
 		assert.equal(inputCalls.length, 1);