feat(amazon-bedrock): forward Anthropic beta flags via additionalMode…

extensions/amazon-bedrock/index.test.ts

@@ -264,19 +264,39 @@ describe("amazon-bedrock provider plugin", () => {
       });
       const result = callWrappedStream(provider, ANTHROPIC_MODEL, ANTHROPIC_MODEL_DESCRIPTOR);
 
-      // Anthropic models should get guardrailConfig
+      // Anthropic models get guardrailConfig + default anthropic_beta flags.
       expect(result._capturedPayload).toEqual({
         guardrailConfig: {
           guardrailIdentifier: "guardrail-anthropic",
           guardrailVersion: "2",
           streamProcessingMode: "async",
           trace: "disabled",
         },
+        additionalModelRequestFields: {
+          anthropic_beta: [
+            "fine-grained-tool-streaming-2025-05-14",
+            "interleaved-thinking-2025-05-14",
+          ],
+        },
       });
       // Anthropic models should NOT get cacheRetention: "none"
       expect(result).not.toHaveProperty("cacheRetention", "none");
     });
 
+    it("injects default anthropic_beta flags for Anthropic Bedrock models without guardrail", async () => {
+      const provider = await registerWithConfig(undefined);
+      const result = callWrappedStream(provider, ANTHROPIC_MODEL, ANTHROPIC_MODEL_DESCRIPTOR);
+
+      expect(result._capturedPayload).toEqual({
+        additionalModelRequestFields: {
+          anthropic_beta: [
+            "fine-grained-tool-streaming-2025-05-14",
+            "interleaved-thinking-2025-05-14",
+          ],
+        },
+      });
+    });
+
     it("injects guardrailConfig for non-Anthropic models with cacheRetention: none", async () => {
       const provider = await registerWithConfig({
         guardrail: {

extensions/amazon-bedrock/register.sync.runtime.ts

@@ -16,6 +16,22 @@
 } from "./api.js";
 import { bedrockMemoryEmbeddingProviderAdapter } from "./memory-embedding-adapter.js";
 
+const PI_AI_DEFAULT_ANTHROPIC_BETAS = [
+  "fine-grained-tool-streaming-2025-05-14",
+  "interleaved-thinking-2025-05-14",
+] as const;
+
+function createBedrockAnthropicBetasWrapper(baseStreamFn: StreamFn | undefined): StreamFn | undefined {
+  if (!baseStreamFn) return baseStreamFn;
+  return (model, context, options) =>
+    streamWithPayloadPatch(baseStreamFn, model, context, options, (payload) => {
+      payload.additionalModelRequestFields = {
+        ...(payload.additionalModelRequestFields as Record<string, unknown> | undefined),
+        anthropic_beta: [...PI_AI_DEFAULT_ANTHROPIC_BETAS],
+      };
+    });
+}
+
 type GuardrailConfig = {
   guardrailIdentifier: string;
   guardrailVersion: string;
@@ -82,7 +98,9 @@
   api.registerMemoryEmbeddingProvider(bedrockMemoryEmbeddingProviderAdapter);
 
   const baseWrapStreamFn = ({ modelId, streamFn }: { modelId: string; streamFn?: StreamFn }) =>
-    isAnthropicBedrockModel(modelId) ? streamFn : createBedrockNoCacheWrapper(streamFn);
+    isAnthropicBedrockModel(modelId)
+      ? createBedrockAnthropicBetasWrapper(streamFn)
+      : createBedrockNoCacheWrapper(streamFn);
 
   const cacheWrapStreamFn =
     guardrail?.guardrailIdentifier && guardrail?.guardrailVersion