feat(ai): add chat-template thinking compat

closes #5673

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

@@ -15,6 +15,7 @@ import { calculateCost, clampThinkingLevel } from "../models.ts";
 import type {
 	AssistantMessage,
 	CacheRetention,
+	ChatTemplateKwargValue,
 	Context,
 	ImageContent,
 	Message,
@@ -91,6 +92,8 @@ type ResolvedOpenAICompletionsCompat = Omit<Required<OpenAICompletionsCompat>, "
 	cacheControlFormat?: OpenAICompletionsCompat["cacheControlFormat"];
 };
 
+type ResolvedChatTemplateKwargValue = string | number | boolean | null;
+
 type ChatCompletionInstructionMessageParam = ChatCompletionDeveloperMessageParam | ChatCompletionSystemMessageParam;
 
 type ChatCompletionTextPartWithCacheControl = ChatCompletionContentPartText & {
@@ -585,6 +588,11 @@ function buildParams(
 			enable_thinking: !!options?.reasoningEffort,
 			preserve_thinking: true,
 		};
+	} else if (compat.thinkingFormat === "chat-template" && model.reasoning) {
+		const chatTemplateKwargs = buildChatTemplateKwargs(model, options, compat);
+		if (chatTemplateKwargs) {
+			(params as any).chat_template_kwargs = chatTemplateKwargs;
+		}
 	} else if (compat.thinkingFormat === "deepseek" && model.reasoning) {
 		if (options?.reasoningEffort) {
 			(params as any).thinking = { type: "enabled" };
@@ -655,6 +663,44 @@ function buildParams(
 	return params;
 }
 
+function buildChatTemplateKwargs(
+	model: Model<"openai-completions">,
+	options: OpenAICompletionsOptions | undefined,
+	compat: ResolvedOpenAICompletionsCompat,
+): Record<string, ResolvedChatTemplateKwargValue> | undefined {
+	const kwargs: Record<string, ResolvedChatTemplateKwargValue> = {};
+
+	for (const [key, value] of Object.entries(compat.chatTemplateKwargs)) {
+		const resolved = resolveChatTemplateKwargValue(model, options, value);
+		if (resolved !== undefined) {
+			kwargs[key] = resolved;
+		}
+	}
+
+	return Object.keys(kwargs).length > 0 ? kwargs : undefined;
+}
+
+function resolveChatTemplateKwargValue(
+	model: Model<"openai-completions">,
+	options: OpenAICompletionsOptions | undefined,
+	value: ChatTemplateKwargValue,
+): ResolvedChatTemplateKwargValue | undefined {
+	if (typeof value !== "object" || value === null) {
+		return value;
+	}
+
+	const reasoningEffort = options?.reasoningEffort;
+	if (!reasoningEffort && value.omitWhenOff) {
+		return undefined;
+	}
+	if (value.$var === "thinking.enabled") {
+		return !!reasoningEffort;
+	}
+
+	const mappedValue = reasoningEffort ? model.thinkingLevelMap?.[reasoningEffort] : model.thinkingLevelMap?.off;
+	return mappedValue === undefined ? reasoningEffort : typeof mappedValue === "string" ? mappedValue : undefined;
+}
+
 function getCompatCacheControl(
 	compat: ResolvedOpenAICompletionsCompat,
 	cacheRetention: CacheRetention,
@@ -1167,6 +1213,7 @@ function detectCompat(model: Model<"openai-completions">): ResolvedOpenAIComplet
 							: "openai",
 		openRouterRouting: {},
 		vercelGatewayRouting: {},
+		chatTemplateKwargs: {},
 		zaiToolStream: false,
 		supportsStrictMode: !isMoonshot && !isTogether && !isCloudflareAiGateway && !isNvidia,
 		cacheControlFormat,
@@ -1205,6 +1252,7 @@ function getCompat(model: Model<"openai-completions">): ResolvedOpenAICompletion
 		thinkingFormat: model.compat.thinkingFormat ?? detected.thinkingFormat,
 		openRouterRouting: model.compat.openRouterRouting ?? {},
 		vercelGatewayRouting: model.compat.vercelGatewayRouting ?? detected.vercelGatewayRouting,
+		chatTemplateKwargs: model.compat.chatTemplateKwargs ?? detected.chatTemplateKwargs,
 		zaiToolStream: model.compat.zaiToolStream ?? detected.zaiToolStream,
 		supportsStrictMode: model.compat.supportsStrictMode ?? detected.supportsStrictMode,
 		cacheControlFormat: model.compat.cacheControlFormat ?? detected.cacheControlFormat,