diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index 2fbf115b..c1a588e6 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed direct Mistral tool definitions to strip TypeBox symbol metadata before passing schemas to the SDK, restoring tool calls after the SDK's stricter outbound validation ([#3361](https://github.com/badlogic/pi-mono/issues/3361))
+
 ## [0.67.67] - 2026-04-17
 
 ### Added
diff --git a/packages/ai/src/providers/mistral.ts b/packages/ai/src/providers/mistral.ts
index 33a74885..68affc98 100644
--- a/packages/ai/src/providers/mistral.ts
+++ b/packages/ai/src/providers/mistral.ts
@@ -456,12 +456,28 @@ function toFunctionTools(tools: Tool[]): Array<FunctionTool & { type: "function"
 		function: {
 			name: tool.name,
 			description: tool.description,
-			parameters: tool.parameters as unknown as Record<string, unknown>,
+			parameters: stripSymbolKeys(tool.parameters) as Record<string, unknown>,
 			strict: false,
 		},
 	}));
 }
 
+function stripSymbolKeys(value: unknown): unknown {
+	if (Array.isArray(value)) {
+		return value.map((item) => stripSymbolKeys(item));
+	}
+
+	if (value && typeof value === "object") {
+		const result: Record<string, unknown> = {};
+		for (const [key, entry] of Object.entries(value)) {
+			result[key] = stripSymbolKeys(entry);
+		}
+		return result;
+	}
+
+	return value;
+}
+
 function toChatMessages(messages: Message[], supportsImages: boolean): ChatCompletionStreamRequestMessage[] {
 	const result: ChatCompletionStreamRequestMessage[] = [];
 
diff --git a/packages/ai/test/mistral-tool-schema.test.ts b/packages/ai/test/mistral-tool-schema.test.ts
new file mode 100644
index 00000000..726aca4c
--- /dev/null
+++ b/packages/ai/test/mistral-tool-schema.test.ts
@@ -0,0 +1,61 @@
+import { Type } from "@sinclair/typebox";
+import { describe, expect, it } from "vitest";
+import { getModel } from "../src/models.js";
+import { complete } from "../src/stream.js";
+import type { Context, Model } from "../src/types.js";
+
+interface MistralToolPayload {
+	tools?: Array<{
+		type: "function";
+		function: {
+			name: string;
+			parameters: Record<string, unknown>;
+		};
+	}>;
+}
+
+describe("Mistral tool schema serialization", () => {
+	it("strips TypeBox symbol keys before the SDK validates tool schemas", async () => {
+		const model: Model<"mistral-conversations"> = {
+			...getModel("mistral", "devstral-medium-latest"),
+			baseUrl: "http://127.0.0.1:9",
+		};
+		const parameters = Type.Object({
+			nested: Type.Object({
+				value: Type.String(),
+			}),
+		});
+		const context: Context = {
+			messages: [{ role: "user", content: "Hi", timestamp: Date.now() }],
+			tools: [
+				{
+					name: "inspect_schema",
+					description: "Inspect the schema",
+					parameters,
+				},
+			],
+		};
+		let capturedPayload: MistralToolPayload | undefined;
+
+		const response = await complete(model, context, {
+			apiKey: "fake-key",
+			onPayload: (payload) => {
+				capturedPayload = payload as MistralToolPayload;
+				return payload;
+			},
+		});
+
+		expect(capturedPayload?.tools).toHaveLength(1);
+		const payloadParameters = capturedPayload?.tools?.[0]?.function.parameters;
+		expect(payloadParameters).toBeDefined();
+		expect(Object.getOwnPropertySymbols(payloadParameters ?? {})).toHaveLength(0);
+		const properties = payloadParameters?.properties;
+		expect(properties).toBeTruthy();
+		expect(Object.getOwnPropertySymbols((properties as Record<string, unknown>) ?? {})).toHaveLength(0);
+		const nested = (properties as Record<string, unknown> | undefined)?.nested;
+		expect(nested).toBeTruthy();
+		expect(Object.getOwnPropertySymbols((nested as Record<string, unknown>) ?? {})).toHaveLength(0);
+		expect(response.stopReason).toBe("error");
+		expect(response.errorMessage).not.toContain("Input validation failed");
+	});
+});
diff --git a/packages/ai/test/stream.test.ts b/packages/ai/test/stream.test.ts
index 16e6f96e..a9f579f4 100644
--- a/packages/ai/test/stream.test.ts
+++ b/packages/ai/test/stream.test.ts
@@ -767,11 +767,12 @@ describe("Generate E2E Tests", () => {
 
 		it("should handle thinking mode", { retry: 3 }, async () => {
 			const llm = getModel("mistral", "magistral-medium-latest");
-			await handleThinking(llm, { reasoningEffort: "medium" });
+			await handleThinking(llm, { promptMode: "reasoning" });
 		});
 
 		it("should handle multi-turn with thinking and tools", { retry: 3 }, async () => {
-			await multiTurn(llm, { reasoningEffort: "medium" });
+			const llm = getModel("mistral", "magistral-medium-latest");
+			await multiTurn(llm, { promptMode: "reasoning" });
 		});
 	});