fix: strip XML tags from kimi-k2-thinking model reasoning output

- Added stripXmlTags method to remove XML tags from reasoning content
- Applied XML tag stripping specifically for moonshot/kimi-k2-thinking model
- Added tests to verify XML tags are stripped for kimi model but preserved for others
- Fixes #9172 where XML tags were displayed in thinking prompts

src/api/providers/__tests__/openrouter.spec.ts

@@ -130,6 +130,109 @@ describe("OpenRouterHandler", () => {
 	})
 
 	describe("createMessage", () => {
+		it("strips XML tags from reasoning content for kimi-k2-thinking model", async () => {
+			const handler = new OpenRouterHandler({
+				...mockOptions,
+				openRouterModelId: "moonshot/kimi-k2-thinking",
+			})
+
+			const mockStream = {
+				async *[Symbol.asyncIterator]() {
+					yield {
+						choices: [
+							{
+								delta: {
+									reasoning:
+										"<thinking>This is reasoning content with <tag>XML tags</tag></thinking>",
+								},
+							},
+						],
+					}
+					yield {
+						choices: [
+							{
+								delta: {
+									content: "Regular content",
+								},
+							},
+						],
+					}
+					yield {
+						usage: {
+							prompt_tokens: 10,
+							completion_tokens: 20,
+						},
+					}
+				},
+			}
+
+			const mockCreate = vitest.fn().mockResolvedValue(mockStream)
+			;(OpenAI as any).prototype.chat = {
+				completions: { create: mockCreate },
+			} as any
+
+			const chunks = []
+			const generator = handler.createMessage("test", [])
+			for await (const chunk of generator) {
+				chunks.push(chunk)
+			}
+
+			// Check that reasoning content has XML tags stripped
+			expect(chunks[0]).toEqual({
+				type: "reasoning",
+				text: "This is reasoning content with XML tags",
+			})
+			expect(chunks[1]).toEqual({
+				type: "text",
+				text: "Regular content",
+			})
+		})
+
+		it("does not strip XML tags from reasoning content for other models", async () => {
+			const handler = new OpenRouterHandler({
+				...mockOptions,
+				openRouterModelId: "openai/gpt-4",
+			})
+
+			const mockStream = {
+				async *[Symbol.asyncIterator]() {
+					yield {
+						choices: [
+							{
+								delta: {
+									reasoning:
+										"<thinking>This is reasoning content with <tag>XML tags</tag></thinking>",
+								},
+							},
+						],
+					}
+					yield {
+						usage: {
+							prompt_tokens: 10,
+							completion_tokens: 20,
+						},
+					}
+				},
+			}
+
+			const mockCreate = vitest.fn().mockResolvedValue(mockStream)
+			;(OpenAI as any).prototype.chat = {
+				completions: { create: mockCreate },
+			} as any
+
+			const chunks = []
+			const generator = handler.createMessage("test", [])
+			for await (const chunk of generator) {
+				chunks.push(chunk)
+			}
+
+			// Check that reasoning content keeps XML tags for non-kimi models
+			expect(chunks[0]).toEqual({
+				type: "reasoning",
+				text: "<thinking>This is reasoning content with <tag>XML tags</tag></thinking>",
+			})
+		})
+
 		it("generates correct stream chunks", async () => {
 			const handler = new OpenRouterHandler(mockOptions)
 

src/api/providers/openrouter.ts

@@ -98,6 +98,15 @@ export class OpenRouterHandler extends BaseProvider implements SingleCompletionH
 		this.client = new OpenAI({ baseURL, apiKey, defaultHeaders: DEFAULT_HEADERS })
 	}
 
+	/**
+	 * Strip XML tags from reasoning content for models that include them
+	 * Some models like kimi-k2-thinking include XML tags in their reasoning output
+	 */
+	private stripXmlTags(text: string): string {
+		// Remove XML tags but preserve the content between them
+		return text.replace(/<[^>]*>/g, "")
+	}
+
 	override async *createMessage(
 		systemPrompt: string,
 		messages: Anthropic.Messages.MessageParam[],
@@ -180,14 +189,21 @@ export class OpenRouterHandler extends BaseProvider implements SingleCompletionH
 				throw new Error(`OpenRouter API Error ${error?.code}: ${error?.message}`)
 			}
 
-			const delta = chunk.choices[0]?.delta
+			const delta = chunk.choices?.[0]?.delta
 
-			if ("reasoning" in delta && delta.reasoning && typeof delta.reasoning === "string") {
-				yield { type: "reasoning", text: delta.reasoning }
-			}
+			if (delta) {
+				const modelId = this.options.openRouterModelId ?? openRouterDefaultModelId
 
-			if (delta?.content) {
-				yield { type: "text", text: delta.content }
+				if ("reasoning" in delta && delta.reasoning && typeof delta.reasoning === "string") {
+					// Strip XML tags for kimi-k2-thinking model which includes them in reasoning output
+					const reasoningText =
+						modelId === "moonshot/kimi-k2-thinking" ? this.stripXmlTags(delta.reasoning) : delta.reasoning
+					yield { type: "reasoning", text: reasoningText }
+				}
+
+				if (delta.content) {
+					yield { type: "text", text: delta.content }
+				}
 			}
 
 			if (chunk.usage) {