fix(ai): use reasoning_effort for Mistral Small 4 closes #3338

package-lock.json

@@ -1781,13 +1781,14 @@
 			"link": true
 		},
 		"node_modules/@mistralai/mistralai": {
-			"version": "1.14.1",
+			"version": "2.2.0",
-			"resolved": "https://registry.npmjs.org/@mistralai/mistralai/-/mistralai-1.14.1.tgz",
+			"resolved": "https://registry.npmjs.org/@mistralai/mistralai/-/mistralai-2.2.0.tgz",
-			"integrity": "sha512-IiLmmZFCCTReQgPAT33r7KQ1nYo5JPdvGkrkZqA8qQ2qB1GHgs5LoP5K2ICyrjnpw2n8oSxMM/VP+liiKcGNlQ==",
+			"integrity": "sha512-JQUGIXjFWnw/J9LpTSf/ZXwVW3Sh8FBAcfTo5QvAHqkl4CfSiIwnjRJhMoAFcP6ncCe84YPU1ncDGX+p3OXnfg==",
+			"license": "Apache-2.0",
 			"dependencies": {
 				"ws": "^8.18.0",
 				"zod": "^3.25.0 || ^4.0.0",
-				"zod-to-json-schema": "^3.24.1"
+				"zod-to-json-schema": "^3.25.0"
 			}
 		},
 		"node_modules/@napi-rs/canvas": {
@@ -8576,7 +8577,7 @@
 				"@anthropic-ai/sdk": "^0.90.0",
 				"@aws-sdk/client-bedrock-runtime": "^3.1030.0",
 				"@google/genai": "^1.40.0",
-				"@mistralai/mistralai": "1.14.1",
+				"@mistralai/mistralai": "^2.2.0",
 				"@sinclair/typebox": "^0.34.41",
 				"ajv": "^8.17.1",
 				"ajv-formats": "^3.0.1",

packages/ai/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed Anthropic and Bedrock adaptive-thinking payload tests to expect the default `display: "summarized"` field when reasoning is enabled.
+- Fixed Mistral Small 4 reasoning requests to use `reasoning_effort` instead of `prompt_mode`, restoring default thinking support for `mistral-small-2603` and `mistral-small-latest` ([#3338](https://github.com/badlogic/pi-mono/issues/3338))
 - Fixed `qwen-chat-template` OpenAI-compatible requests to set `chat_template_kwargs.preserve_thinking: true`, preserving prior Qwen thinking across turns so multi-turn tool calls keep their arguments instead of degrading to empty `{}` payloads ([#3325](https://github.com/badlogic/pi-mono/issues/3325))
 
 ## [0.67.6] - 2026-04-16

packages/ai/package.json

@@ -75,7 +75,7 @@
 		"@anthropic-ai/sdk": "^0.90.0",
 		"@aws-sdk/client-bedrock-runtime": "^3.1030.0",
 		"@google/genai": "^1.40.0",
-		"@mistralai/mistralai": "1.14.1",
+		"@mistralai/mistralai": "^2.2.0",
 		"@sinclair/typebox": "^0.34.41",
 		"ajv": "^8.17.1",
 		"ajv-formats": "^3.0.1",

packages/ai/src/providers/mistral.ts

@@ -1,12 +1,11 @@
 import { Mistral } from "@mistralai/mistralai";
-import type { RequestOptions } from "@mistralai/mistralai/lib/sdks.js";
 import type {
 	ChatCompletionStreamRequest,
-	ChatCompletionStreamRequestMessages,
+	ChatCompletionStreamRequestMessage,
 	CompletionEvent,
 	ContentChunk,
 	FunctionTool,
-} from "@mistralai/mistralai/models/components/index.js";
+} from "@mistralai/mistralai/models/components";
 import { getEnvApiKey } from "../env-api-keys.js";
 import { calculateCost } from "../models.js";
 import type {
@@ -36,9 +35,12 @@ const MAX_MISTRAL_ERROR_BODY_CHARS = 4000;
 /**
  * Provider-specific options for the Mistral API.
  */
+type MistralReasoningEffort = "none" | "high";
+
 export interface MistralOptions extends StreamOptions {
 	toolChoice?: "auto" | "none" | "any" | "required" | { type: "function"; function: { name: string } };
 	promptMode?: "reasoning";
+	reasoningEffort?: MistralReasoningEffort;
 }
 
 /**
@@ -118,10 +120,12 @@ export const streamSimpleMistral: StreamFunction<"mistral-conversations", Simple
 
 	const base = buildBaseOptions(model, options, apiKey);
 	const reasoning = clampReasoning(options?.reasoning);
+	const shouldUseReasoning = model.reasoning && reasoning !== undefined;
 
 	return streamMistral(model, context, {
 		...base,
-		promptMode: model.reasoning && reasoning ? "reasoning" : undefined,
+		promptMode: shouldUseReasoning && usesPromptModeReasoning(model) ? "reasoning" : undefined,
+		reasoningEffort: shouldUseReasoning && usesReasoningEffort(model) ? mapReasoningEffort(reasoning) : undefined,
 	} satisfies MistralOptions);
 };
 
@@ -205,10 +209,15 @@ function safeJsonStringify(value: unknown): string {
 	}
 }
 
-function buildRequestOptions(model: Model<"mistral-conversations">, options?: MistralOptions): RequestOptions {
+function buildRequestOptions(model: Model<"mistral-conversations">, options?: MistralOptions) {
-	const requestOptions: RequestOptions = {};
+	const requestOptions: {
+		signal?: AbortSignal;
+		retries: { strategy: "none" };
+		headers?: Record<string, string>;
+	} = {
+		retries: { strategy: "none" },
+	};
 	if (options?.signal) requestOptions.signal = options.signal;
-	requestOptions.retries = { strategy: "none" };
 
 	const headers: Record<string, string> = {};
 	if (model.headers) Object.assign(headers, model.headers);
@@ -243,7 +252,8 @@ function buildChatPayload(
 	if (options?.temperature !== undefined) payload.temperature = options.temperature;
 	if (options?.maxTokens !== undefined) payload.maxTokens = options.maxTokens;
 	if (options?.toolChoice) payload.toolChoice = mapToolChoice(options.toolChoice);
-	if (options?.promptMode) payload.promptMode = options.promptMode as any;
+	if (options?.promptMode) payload.promptMode = options.promptMode;
+	if (options?.reasoningEffort) payload.reasoningEffort = options.reasoningEffort;
 
 	if (context.systemPrompt) {
 		payload.messages.unshift({
@@ -452,8 +462,8 @@ function toFunctionTools(tools: Tool[]): Array<FunctionTool & { type: "function"
 	}));
 }
 
-function toChatMessages(messages: Message[], supportsImages: boolean): ChatCompletionStreamRequestMessages[] {
+function toChatMessages(messages: Message[], supportsImages: boolean): ChatCompletionStreamRequestMessage[] {
-	const result: ChatCompletionStreamRequestMessages[] = [];
+	const result: ChatCompletionStreamRequestMessage[] = [];
 
 	for (const msg of messages) {
 		if (msg.role === "user") {
@@ -505,7 +515,7 @@ function toChatMessages(messages: Message[], supportsImages: boolean): ChatCompl
 				});
 			}
 
-			const assistantMessage: ChatCompletionStreamRequestMessages = { role: "assistant" };
+			const assistantMessage: ChatCompletionStreamRequestMessage = { role: "assistant" };
 			if (contentParts.length > 0) assistantMessage.content = contentParts;
 			if (toolCalls.length > 0) assistantMessage.toolCalls = toolCalls;
 			if (contentParts.length > 0 || toolCalls.length > 0) result.push(assistantMessage);
@@ -560,6 +570,18 @@ function buildToolResultText(text: string, hasImages: boolean, supportsImages: b
 	return isError ? "[tool error] (no tool output)" : "(no tool output)";
 }
 
+function usesReasoningEffort(model: Model<"mistral-conversations">): boolean {
+	return model.id === "mistral-small-2603" || model.id === "mistral-small-latest";
+}
+
+function usesPromptModeReasoning(model: Model<"mistral-conversations">): boolean {
+	return model.reasoning && !usesReasoningEffort(model);
+}
+
+function mapReasoningEffort(_level: Exclude<SimpleStreamOptions["reasoning"], undefined>): MistralReasoningEffort {
+	return "high";
+}
+
 function mapToolChoice(
 	choice: MistralOptions["toolChoice"],
 ): "auto" | "none" | "any" | "required" | { type: "function"; function: { name: string } } | undefined {

packages/ai/test/mistral-reasoning-mode.test.ts

@@ -0,0 +1,66 @@
+import { describe, expect, it } from "vitest";
+import { getModel } from "../src/models.js";
+import { streamSimple } from "../src/stream.js";
+import type { Context, Model, SimpleStreamOptions } from "../src/types.js";
+
+interface MistralPayload {
+	promptMode?: "reasoning";
+	reasoningEffort?: "none" | "high";
+}
+
+function makeContext(): Context {
+	return {
+		messages: [{ role: "user", content: "Hello", timestamp: Date.now() }],
+	};
+}
+
+async function capturePayload(
+	model: Model<"mistral-conversations">,
+	options?: SimpleStreamOptions,
+): Promise<MistralPayload> {
+	let capturedPayload: MistralPayload | undefined;
+	const payloadCaptureModel: Model<"mistral-conversations"> = {
+		...model,
+		baseUrl: "http://127.0.0.1:9",
+	};
+
+	const stream = streamSimple(payloadCaptureModel, makeContext(), {
+		...options,
+		apiKey: "fake-key",
+		onPayload: (payload) => {
+			capturedPayload = payload as MistralPayload;
+			return payload;
+		},
+	});
+
+	await stream.result();
+
+	if (!capturedPayload) {
+		throw new Error("Expected payload to be captured before request failure");
+	}
+
+	return capturedPayload;
+}
+
+describe("Mistral reasoning mode selection", () => {
+	it("uses reasoning_effort for Mistral Small 4", async () => {
+		const payload = await capturePayload(getModel("mistral", "mistral-small-2603"), { reasoning: "medium" });
+
+		expect(payload.reasoningEffort).toBe("high");
+		expect(payload.promptMode).toBeUndefined();
+	});
+
+	it("omits reasoning controls for Mistral Small 4 when thinking is off", async () => {
+		const payload = await capturePayload(getModel("mistral", "mistral-small-2603"));
+
+		expect(payload.reasoningEffort).toBeUndefined();
+		expect(payload.promptMode).toBeUndefined();
+	});
+
+	it("uses prompt_mode for Magistral reasoning models", async () => {
+		const payload = await capturePayload(getModel("mistral", "magistral-medium-latest"), { reasoning: "medium" });
+
+		expect(payload.promptMode).toBe("reasoning");
+		expect(payload.reasoningEffort).toBeUndefined();
+	});
+});

packages/coding-agent/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed `/scoped-models` Alt+Up/Down to stay a no-op in the implicit `all enabled` state instead of materializing a full explicit enabled-model list and marking the selector dirty ([#3331](https://github.com/badlogic/pi-mono/issues/3331))
+- Fixed Mistral Small 4 default thinking requests to use the model's supported reasoning control, avoiding `400` errors when starting sessions on `mistral-small-2603` and `mistral-small-latest` ([#3338](https://github.com/badlogic/pi-mono/issues/3338))
 - Fixed flaky git package update notifications by waiting for captured git command stdio to fully drain before comparing local and remote commit SHAs ([#3027](https://github.com/badlogic/pi-mono/issues/3027))
 - Fixed auto-retry transient error detection to treat `Network connection lost.` as retryable, so dropped provider connections retry instead of terminating the agent ([#3317](https://github.com/badlogic/pi-mono/issues/3317))
 - Fixed compact interactive extension startup summaries to disambiguate package extensions and repeated local `index.ts` entries by using package-aware labels and the minimal parent path needed to make local entries unique ([#3308](https://github.com/badlogic/pi-mono/issues/3308))