fix(ai): default unknown providers to non-strict tools (closes #9816)

packages/ai/CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - Added model image-input limit and cache-safe resize metadata to the generated catalog ([#9631](https://github.com/earendil-works/pi/issues/9631)).
 
+### Fixed
+
+- Fixed unknown OpenAI-compatible Chat Completions endpoints receiving strict tool schemas unless they explicitly advertise support, while preserving strict tools for capable built-in models ([#9816](https://github.com/earendil-works/pi/issues/9816)).
+
 ## [0.86.1] - 2026-09-20
 
 ### Added

packages/ai/README.md

@@ -1213,7 +1213,7 @@ interface OpenAICompletionsCompat {
   supportsDeveloperRole?: boolean;   // Whether provider supports `developer` role vs `system` (default: true)
   supportsReasoningEffort?: boolean; // Whether provider supports `reasoning_effort` (default: true)
   supportsUsageInStreaming?: boolean; // Whether provider supports `stream_options: { include_usage: true }` (default: true)
-  supportsStrictMode?: boolean;      // Whether provider supports `strict` in tool definitions (default: true)
+  supportsStrictMode?: boolean;      // Whether provider supports `strict` in tool definitions (default: false; enabled in metadata for capable built-in models)
   supportsOpenAIGrammarTools?: boolean; // Whether to emit OpenAI custom Lark/regex grammar tools; false falls back to normal function tools (default: false; the generated catalog enables it for capable models)
   supportsMidConvoSystemMessages?: boolean; // Whether the model accepts system messages after the conversation started; false folds them into the leading prompt (default: false; the generated catalog enables it for verified models)
   supportsMidConvoToolAdditions?: boolean; // Whether system messages can add tools mid-conversation via Kimi-style `tools` system messages; requires supportsMidConvoSystemMessages (default: false)

packages/ai/scripts/generate-models.ts

@@ -640,7 +640,7 @@ const OPENAI_COMPLETIONS_DEFAULT_COMPAT = {
 	chatTemplateKwargs: {},
 	chatTemplateArgs: {},
 	zaiToolStream: false,
-	supportsStrictMode: true,
+	supportsStrictMode: false,
 	supportsOpenAIGrammarTools: false,
 	supportsMidConvoSystemMessages: false,
 	supportsMidConvoToolAdditions: false,
@@ -744,6 +744,7 @@ function detectOpenAICompletionsCompat(model: Model<"openai-completions">): Open
 		chatTemplateKwargs: {},
 		chatTemplateArgs: {},
 		zaiToolStream: false,
+		// Preserve built-in behavior as explicit metadata against the conservative runtime default.
 		supportsStrictMode: !isMoonshot && !isTogether && !isCloudflareAiGateway && !isNvidia && !isCerebras,
 		supportsOpenAIGrammarTools: false,
 		supportsMidConvoSystemMessages: false,

packages/ai/src/api/openai-completions.ts

@@ -1661,7 +1661,8 @@ function detectCompat(model: Model<"openai-completions">): ResolvedOpenAIComplet
 		zaiToolStream: false,
 		supportsThinkingTokenBudget: false,
 		thinkingTokenBudgetField: undefined,
-		supportsStrictMode: !isMoonshot && !isTogether && !isCloudflareAiGateway && !isNvidia && !isCerebras,
+		// OpenAI compatibility alone does not imply strict JSON-schema tool support.
+		supportsStrictMode: false,
 		supportsOpenAIGrammarTools: false,
 		supportsMidConvoSystemMessages: false,
 		supportsMidConvoToolAdditions: false,

packages/ai/src/types.ts

@@ -731,7 +731,7 @@ export interface OpenAICompletionsCompat {
 	supportsMidConvoSystemMessages?: boolean;
 	/** Whether system messages can introduce additional tools mid-conversation. Requires `supportsMidConvoSystemMessages`. Default: false; the generated model catalog enables it for capable models. */
 	supportsMidConvoToolAdditions?: boolean;
-	/** Whether the provider supports the `strict` field in tool definitions. Default: true. */
+	/** Whether the provider supports the `strict` field in tool definitions. Default: false; generated capable models enable it explicitly. */
 	supportsStrictMode?: boolean;
 	/** Cache control convention for prompt caching. "anthropic" applies Anthropic-style `cache_control` markers to the system prompt, last tool definition, and last user, assistant, or tool-result text content. */
 	cacheControlFormat?: "anthropic";

packages/ai/test/openai-completions-tool-choice.test.ts

@@ -219,6 +219,82 @@ describe("openai-completions tool_choice", () => {
 		expect("strict" in (tool ?? {})).toBe(false);
 	});
 
+	it("defaults unknown OpenAI-compatible endpoints to non-strict tools", async () => {
+		// Regression test for #9816.
+		const model = {
+			...localOpenAICompletionsModel,
+			id: "local-model",
+			name: "Local Model",
+		} satisfies Model<"openai-completions">;
+		const tool: Tool = {
+			name: "ping",
+			description: "Ping tool",
+			parameters: Type.Object({
+				required: Type.String(),
+				optional: Type.Optional(Type.String()),
+			}),
+			constrainedSampling: { type: "json_schema", strict: "prefer" },
+		};
+		let payload: unknown;
+
+		await streamSimple(
+			model,
+			{
+				messages: [{ role: "user", content: "Call ping", timestamp: Date.now() }],
+				tools: [tool],
+			},
+			{
+				apiKey: "test",
+				onPayload: (params: unknown) => {
+					payload = params;
+				},
+			},
+		).result();
+
+		const params = (payload ?? mockState.lastParams) as {
+			tools?: Array<{ function?: { strict?: boolean; parameters?: { required?: string[] } } }>;
+		};
+		const functionTool = params.tools?.[0]?.function;
+		expect(functionTool).not.toHaveProperty("strict");
+		expect(functionTool?.parameters?.required).toEqual(["required"]);
+	});
+
+	it("preserves strict tools for capable built-in Chat Completions models", async () => {
+		const model = getModel("groq", "openai/gpt-oss-20b")!;
+		expect(model.compat?.supportsStrictMode).toBe(true);
+		const tool: Tool = {
+			name: "ping",
+			description: "Ping tool",
+			parameters: Type.Object({
+				required: Type.String(),
+				optional: Type.Optional(Type.String()),
+			}),
+			constrainedSampling: { type: "json_schema", strict: "prefer" },
+		};
+		let payload: unknown;
+
+		await streamSimple(
+			model,
+			{
+				messages: [{ role: "user", content: "Call ping", timestamp: Date.now() }],
+				tools: [tool],
+			},
+			{
+				apiKey: "test",
+				onPayload: (params: unknown) => {
+					payload = params;
+				},
+			},
+		).result();
+
+		const params = (payload ?? mockState.lastParams) as {
+			tools?: Array<{ function?: { strict?: boolean; parameters?: { required?: string[] } } }>;
+		};
+		const functionTool = params.tools?.[0]?.function;
+		expect(functionTool?.strict).toBe(true);
+		expect(functionTool?.parameters?.required).toEqual(["required", "optional"]);
+	});
+
 	it("maps Groq Qwen reasoning levels to default reasoning_effort", async () => {
 		const model = getModel("groq", "qwen/qwen3.6-27b")!;
 		let payload: unknown;
@@ -1799,7 +1875,7 @@ describe("openai-completions tool_choice", () => {
 			thinkingFormat: "ant-ling",
 			supportsLongCacheRetention: false,
 		});
-		expect(model.compat?.supportsStrictMode).toBeUndefined();
+		expect(model.compat?.supportsStrictMode).toBe(true);
 		expect(model.compat?.requiresReasoningContentOnAssistantMessages).toBeUndefined();
 
 		await streamSimple(