Agents SDK v0.6.0: RPC transport for MCP, optional OAuth, hardened schema conversion, and @cloudflare/ai-chat fixes

The latest release of the Agents SDK lets you define an Agent and an McpAgent in the same Worker and connect them over RPC — no HTTP, no network overhead. It also makes OAuth opt-in for simple MCP connections, hardens the schema converter for production workloads, and ships a batch of @cloudflare/ai-chat reliability fixes.

RPC transport for MCP

You can now connect an Agent to an McpAgent in the same Worker using a Durable Object binding instead of an HTTP URL. The connection stays entirely within the Cloudflare runtime — no network round-trips, no serialization overhead.

Pass the Durable Object namespace directly to addMcpServer:

import { Agent } from "agents"; export class MyAgent extends Agent { async onStart() { // Connect via DO binding — no HTTP, no network overhead await this.addMcpServer("counter", env.MY_MCP); // With props for per-user context await this.addMcpServer("counter", env.MY_MCP, { props: { userId: "user-123", role: "admin" }, }); } }

import { Agent } from "agents"; export class MyAgent extends Agent { async onStart() { // Connect via DO binding — no HTTP, no network overhead await this.addMcpServer("counter", env.MY_MCP); // With props for per-user context await this.addMcpServer("counter", env.MY_MCP, { props: { userId: "user-123", role: "admin" }, }); } }

The addMcpServer method now accepts string | DurableObjectNamespace as the second parameter with full TypeScript overloads, so HTTP and RPC paths are type-safe and cannot be mixed.

Key capabilities:

• Hibernation support — RPC connections survive Durable Object hibernation automatically. The binding name and props are persisted to storage and restored on wake-up, matching the behavior of HTTP MCP connections.
• Deduplication — Calling addMcpServer with the same server name returns the existing connection instead of creating duplicates. Connection IDs are stable across hibernation restore.
• Smaller surface area — The RPC transport internals have been rewritten and reduced from 609 lines to 245 lines. RPCServerTransport now uses JSONRPCMessageSchema from the MCP SDK for validation instead of hand-written checks.

Note

RPC transport is experimental. The API may change based on feedback. Refer to the tracking issue for updates.

Optional OAuth for MCP connections

addMcpServer() no longer eagerly creates an OAuth provider for every connection. For servers that do not require authentication, a simple call is all you need:

// No callbackHost, no OAuth config — just works await this.addMcpServer("my-server", "https://mcp.example.com");

// No callbackHost, no OAuth config — just works await this.addMcpServer("my-server", "https://mcp.example.com");

If the server responds with a 401, the SDK throws a clear error: "This MCP server requires OAuth authentication. Provide callbackHost in addMcpServer options to enable the OAuth flow." The restore-from-storage flow also handles missing callback URLs gracefully, skipping auth provider creation for non-OAuth servers.

Hardened JSON Schema to TypeScript converter

The schema converter used by generateTypes() and getAITools() now handles edge cases that previously caused crashes in production:

• Depth and circular reference guards — Prevents stack overflows on recursive or deeply nested schemas
• $ref resolution — Supports internal JSON Pointers (#/definitions/..., #/$defs/..., #)
• Tuple support — prefixItems (JSON Schema 2020-12) and array items (draft-07)
• OpenAPI 3.0 nullable: true — Supported across all schema branches
• Per-tool error isolation — One malformed schema cannot crash the full pipeline in generateTypes() or getAITools()
• Missing inputSchema fallback — getAITools() falls back to { type: "object" } instead of throwing

@cloudflare/ai-chat fixes

• Tool denial flow — Denied tool approvals (approved: false) now transition to output-denied with a tool_result, fixing Anthropic provider compatibility. Custom denial messages are supported via state: "output-error" and errorText.
• Abort/cancel support — Streaming responses now properly cancel the reader loop when the abort signal fires and send a done signal to the client.
• Duplicate message persistence — persistMessages() now reconciles assistant messages by content and order, preventing duplicate rows when clients resend full history.
• requestId in OnChatMessageOptions — Handlers can now send properly-tagged error responses for pre-stream failures.
• redacted_thinking preservation — The message sanitizer no longer strips Anthropic redacted_thinking blocks.
• /get-messages reliability — Endpoint handling moved from a prototype onRequest() override to a constructor wrapper, so it works even when users override onRequest without calling super.onRequest().
• Client tool APIs undeprecated — createToolsFromClientSchemas, clientTools, AITool, extractClientToolSchemas, and the tools option on useAgentChat are restored for SDK use cases where tools are defined dynamically at runtime.
• jsonSchema initialization — Fixed jsonSchema not initialized error when calling getAITools() in onChatMessage.

Upgrade

To update to the latest version:

npm i agents@latest @cloudflare/ai-chat@latest