fix(ai): support Anthropic eager tool streaming compat

closes #3575

packages/ai/src/models.generated.ts

@@ -3014,6 +3014,7 @@ export const MODELS = {
 			provider: "github-copilot",
 			baseUrl: "https://api.individual.githubcopilot.com",
 			headers: {"User-Agent":"GitHubCopilotChat/0.35.0","Editor-Version":"vscode/1.107.0","Editor-Plugin-Version":"copilot-chat/0.35.0","Copilot-Integration-Id":"vscode-chat"},
+			compat: {"supportsEagerToolInputStreaming":false},
 			reasoning: true,
 			input: ["text", "image"],
 			cost: {

packages/ai/src/providers/anthropic.ts

@@ -9,6 +9,7 @@ import type {
 import { getEnvApiKey } from "../env-api-keys.js";
 import { calculateCost } from "../models.js";
 import type {
+	AnthropicMessagesCompat,
 	Api,
 	AssistantMessage,
 	CacheRetention,
@@ -159,6 +160,15 @@ export type AnthropicEffort = "low" | "medium" | "high" | "xhigh" | "max";
 
 export type AnthropicThinkingDisplay = "summarized" | "omitted";
 
+const FINE_GRAINED_TOOL_STREAMING_BETA = "fine-grained-tool-streaming-2025-05-14";
+const INTERLEAVED_THINKING_BETA = "interleaved-thinking-2025-05-14";
+
+function getAnthropicCompat(model: Model<"anthropic-messages">): Required<AnthropicMessagesCompat> {
+	return {
+		supportsEagerToolInputStreaming: model.compat?.supportsEagerToolInputStreaming ?? true,
+	};
+}
+
 export interface AnthropicOptions extends StreamOptions {
 	/**
 	 * Enable extended thinking.
@@ -433,6 +443,7 @@ export const streamAnthropic: StreamFunction<"anthropic-messages", AnthropicOpti
 					model,
 					apiKey,
 					options?.interleavedThinking ?? true,
+					shouldUseFineGrainedToolStreamingBeta(model, context),
 					options?.headers,
 					copilotDynamicHeaders,
 				);
@@ -728,6 +739,7 @@ function createClient(
 	model: Model<"anthropic-messages">,
 	apiKey: string,
 	interleavedThinking: boolean,
+	useFineGrainedToolStreamingBeta: boolean,
 	optionsHeaders?: Record<string, string>,
 	dynamicHeaders?: Record<string, string>,
 ): { client: Anthropic; isOAuthToken: boolean } {
@@ -735,11 +747,14 @@ function createClient(
 	// The beta header is deprecated on Opus 4.6 and redundant on Sonnet 4.6, so skip it.
 	const needsInterleavedBeta = interleavedThinking && !supportsAdaptiveThinking(model.id);
 
-	// Copilot: Bearer auth, selective betas (no fine-grained-tool-streaming)
+	// Copilot: Bearer auth, selective betas.
 	if (model.provider === "github-copilot") {
 		const betaFeatures: string[] = [];
+		if (useFineGrainedToolStreamingBeta) {
+			betaFeatures.push(FINE_GRAINED_TOOL_STREAMING_BETA);
+		}
 		if (needsInterleavedBeta) {
-			betaFeatures.push("interleaved-thinking-2025-05-14");
+			betaFeatures.push(INTERLEAVED_THINKING_BETA);
 		}
 
 		const client = new Anthropic({
@@ -763,8 +778,11 @@ function createClient(
 	}
 
 	const betaFeatures: string[] = [];
+	if (useFineGrainedToolStreamingBeta) {
+		betaFeatures.push(FINE_GRAINED_TOOL_STREAMING_BETA);
+	}
 	if (needsInterleavedBeta) {
-		betaFeatures.push("interleaved-thinking-2025-05-14");
+		betaFeatures.push(INTERLEAVED_THINKING_BETA);
 	}
 
 	// OAuth: Bearer auth, Claude Code identity headers
@@ -856,7 +874,12 @@ function buildParams(
 	}
 
 	if (context.tools) {
-		params.tools = convertTools(context.tools, isOAuthToken, cacheControl);
+		params.tools = convertTools(
+			context.tools,
+			isOAuthToken,
+			getAnthropicCompat(model).supportsEagerToolInputStreaming,
+			cacheControl,
+		);
 	}
 
 	// Configure thinking mode: adaptive (Opus 4.6+ and Sonnet 4.6),
@@ -1078,9 +1101,14 @@ function convertMessages(
 	return params;
 }
 
+function shouldUseFineGrainedToolStreamingBeta(model: Model<"anthropic-messages">, context: Context): boolean {
+	return !!context.tools?.length && !getAnthropicCompat(model).supportsEagerToolInputStreaming;
+}
+
 function convertTools(
 	tools: Tool[],
 	isOAuthToken: boolean,
+	supportsEagerToolInputStreaming: boolean,
 	cacheControl?: CacheControlEphemeral,
 ): Anthropic.Messages.Tool[] {
 	if (!tools) return [];
@@ -1091,7 +1119,7 @@ function convertTools(
 		return {
 			name: isOAuthToken ? toClaudeCodeName(tool.name) : tool.name,
 			description: tool.description,
-			eager_input_streaming: true,
+			...(supportsEagerToolInputStreaming ? { eager_input_streaming: true } : {}),
 			input_schema: {
 				type: "object",
 				properties: schema.properties ?? {},

packages/ai/src/types.ts

@@ -304,6 +304,18 @@ export interface OpenAIResponsesCompat {
 	sendSessionIdHeader?: boolean;
 }
 
+/** Compatibility settings for Anthropic Messages-compatible APIs. */
+export interface AnthropicMessagesCompat {
+	/**
+	 * Whether the provider accepts per-tool `eager_input_streaming`.
+	 * When false, the Anthropic provider omits `tools[].eager_input_streaming`
+	 * and sends the legacy `fine-grained-tool-streaming-2025-05-14` beta header
+	 * for tool-enabled requests.
+	 * Default: true.
+	 */
+	supportsEagerToolInputStreaming?: boolean;
+}
+
 /**
  * OpenRouter provider routing preferences.
  * Controls which upstream providers OpenRouter routes requests to.
@@ -414,5 +426,7 @@ export interface Model<TApi extends Api> {
 		? OpenAICompletionsCompat
 		: TApi extends "openai-responses"
 			? OpenAIResponsesCompat
-			: never;
+			: TApi extends "anthropic-messages"
+				? AnthropicMessagesCompat
+				: never;
 }