diff --git a/src/api/providers/__tests__/openrouter.spec.ts b/src/api/providers/__tests__/openrouter.spec.ts
index 118be755d7..170cbfc7c6 100644
--- a/src/api/providers/__tests__/openrouter.spec.ts
+++ b/src/api/providers/__tests__/openrouter.spec.ts
@@ -75,6 +75,7 @@ describe("OpenRouterHandler", () => {
 				"HTTP-Referer": "https://github.com/RooVetGit/Roo-Cline",
 				"X-Title": "Roo Code",
 				"User-Agent": `RooCode/${Package.version}`,
+				"x-anthropic-beta": "fine-grained-tool-streaming-2025-05-14",
 			},
 		})
 	})
diff --git a/src/api/providers/openrouter.ts b/src/api/providers/openrouter.ts
index 3db61087ef..2327d8599e 100644
--- a/src/api/providers/openrouter.ts
+++ b/src/api/providers/openrouter.ts
@@ -72,7 +72,14 @@ export class OpenRouterHandler extends BaseProvider implements SingleCompletionH
 		const baseURL = this.options.openRouterBaseUrl || "https://openrouter.ai/api/v1"
 		const apiKey = this.options.openRouterApiKey ?? "not-provided"
 
-		this.client = new OpenAI({ baseURL, apiKey, defaultHeaders: DEFAULT_HEADERS })
+		this.client = new OpenAI({
+			baseURL,
+			apiKey,
+			defaultHeaders: {
+				...DEFAULT_HEADERS,
+				"x-anthropic-beta": "fine-grained-tool-streaming-2025-05-14",
+			},
+		})
 
 		// Load models asynchronously to populate cache before getModel() is called
 		this.loadDynamicModels().catch((error) => {