Fix OpenRouter Kimi reasoning compat

closes #5309

packages/ai/CHANGELOG.md

@@ -10,6 +10,7 @@
 
 - Fixed Amazon Bedrock requests to replace blank required user/tool-result text with a placeholder and skip blank replay text blocks ([#4975](https://github.com/earendil-works/pi/issues/4975)).
 - Fixed OpenAI GPT-5.5 generated metadata to omit unsupported minimal thinking ([#5243](https://github.com/earendil-works/pi/issues/5243)).
+- Fixed OpenRouter Kimi K2.6 thinking replay and preserved developer-role instructions for OpenRouter OpenAI and Anthropic models ([#5309](https://github.com/earendil-works/pi/issues/5309)).
 - Fixed GitHub Copilot and OpenRouter test model references that became stale after model regeneration.
 
 ## [0.78.0] - 2026-05-29

packages/ai/scripts/generate-models.ts

@@ -1343,7 +1343,11 @@ async function generateModels() {
 			candidate.maxTokens = 4096;
 		}
 		if (candidate.provider === "openrouter" && candidate.id.startsWith("moonshotai/kimi-k2.6")) {
-			candidate.compat = { ...candidate.compat, supportsDeveloperRole: false };
+			candidate.compat = {
+				...candidate.compat,
+				supportsDeveloperRole: false,
+				requiresReasoningContentOnAssistantMessages: true,
+			};
 		}
 		if (candidate.provider === "openrouter" && candidate.id === "z-ai/glm-5") {
 			candidate.cost.input = 0.6;

packages/ai/src/models.generated.ts

@@ -10281,7 +10281,7 @@ export const MODELS = {
 			api: "openai-completions",
 			provider: "openrouter",
 			baseUrl: "https://openrouter.ai/api/v1",
-			compat: {"supportsDeveloperRole":false},
+			compat: {"supportsDeveloperRole":false,"requiresReasoningContentOnAssistantMessages":true},
 			reasoning: true,
 			input: ["text", "image"],
 			cost: {
@@ -10299,7 +10299,7 @@ export const MODELS = {
 			api: "openai-completions",
 			provider: "openrouter",
 			baseUrl: "https://openrouter.ai/api/v1",
-			compat: {"supportsDeveloperRole":false},
+			compat: {"supportsDeveloperRole":false,"requiresReasoningContentOnAssistantMessages":true},
 			reasoning: true,
 			input: ["text", "image"],
 			cost: {

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

@@ -1100,11 +1100,13 @@ function detectCompat(model: Model<"openai-completions">): ResolvedOpenAIComplet
 
 	const isGrok = provider === "xai" || baseUrl.includes("api.x.ai");
 	const isDeepSeek = provider === "deepseek" || baseUrl.includes("deepseek.com");
+	const isOpenRouterDeveloperRoleModel =
+		isOpenRouter && (model.id.startsWith("anthropic/") || model.id.startsWith("openai/"));
 	const cacheControlFormat = provider === "openrouter" && model.id.startsWith("anthropic/") ? "anthropic" : undefined;
 
 	return {
 		supportsStore: !isNonStandard,
-		supportsDeveloperRole: !isNonStandard && !isOpenRouter,
+		supportsDeveloperRole: isOpenRouterDeveloperRoleModel || (!isNonStandard && !isOpenRouter),
 		supportsReasoningEffort: !isGrok && !isZai && !isMoonshot && !isTogether && !isCloudflareAiGateway && !isNvidia,
 		supportsUsageInStreaming: true,
 		maxTokensField: useMaxTokens ? "max_tokens" : "max_completion_tokens",

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

@@ -817,7 +817,7 @@ describe("openai-completions tool_choice", () => {
 		expect(writeCall).not.toHaveProperty("partialArgs");
 	});
 
-	it("uses system messages for OpenRouter reasoning model instructions", async () => {
+	it("uses system messages for non-OpenAI/Anthropic OpenRouter reasoning model instructions", async () => {
 		const model = getModel("openrouter", "deepseek/deepseek-v4-pro")!;
 		let payload: unknown;
 
@@ -839,6 +839,33 @@ describe("openai-completions tool_choice", () => {
 		expect(params.messages?.[0]?.role).toBe("system");
 	});
 
+	it("keeps developer messages for OpenAI and Anthropic OpenRouter reasoning model instructions", async () => {
+		for (const model of [
+			getModel("openrouter", "openai/gpt-5.2-codex"),
+			getModel("openrouter", "anthropic/claude-sonnet-4.5"),
+		]) {
+			expect(model).toBeDefined();
+			let payload: unknown;
+
+			await streamSimple(
+				model!,
+				{
+					systemPrompt: "Follow instructions.",
+					messages: [{ role: "user", content: "Hi", timestamp: Date.now() }],
+				},
+				{
+					apiKey: "test",
+					onPayload: (params: unknown) => {
+						payload = params;
+					},
+				},
+			).result();
+
+			const params = payload as { messages?: Array<{ role?: string }> };
+			expect(params.messages?.[0]?.role).toBe("developer");
+		}
+	});
+
 	it("keeps developer messages for OpenAI reasoning model instructions", async () => {
 		const { compat: _compat, ...baseModel } = getModel("openai", "gpt-5.5")!;
 		const model = { ...baseModel, api: "openai-completions" } as const;
@@ -862,6 +889,14 @@ describe("openai-completions tool_choice", () => {
 		expect(params.messages?.[0]?.role).toBe("developer");
 	});
 
+	it("stores OpenRouter Kimi K2.6 reasoning replay compat in built-in metadata", () => {
+		for (const modelId of ["moonshotai/kimi-k2.6", "moonshotai/kimi-k2.6:free"] as const) {
+			const model = getModel("openrouter", modelId)!;
+			expect(model.compat?.supportsDeveloperRole).toBe(false);
+			expect(model.compat?.requiresReasoningContentOnAssistantMessages).toBe(true);
+		}
+	});
+
 	it("stores Xiaomi MiMo reasoning replay compat in built-in metadata", () => {
 		const providers = ["xiaomi", "xiaomi-token-plan-cn", "xiaomi-token-plan-ams", "xiaomi-token-plan-sgp"] as const;