Castari Proxy

Castari Proxy

Castari Proxy lets you run the Claude Agent SDK against any model—including OpenRouter catalog models—without changing your agent logic. Install the castari-proxy wrapper, point it at the hosted Castari Worker, and keep using the same SDK APIs. The worker translates Anthropic-style Messages requests to whichever upstream (Anthropic or OpenRouter) matches the model string you provide.
Don't want to hit the hosted worker? See Self-Hosting the Worker for instructions to deploy your own copy.

Repo Overview

This repository contains three main components that work together to enable multi-provider support for the Claude Agent SDK:

1. Wrapper Package (src/)
The castari-proxy npm package provides queryCastari(), a drop-in replacement for the SDK's query() function. It:
- Resolves which provider to use based on the model string (e.g., or:gpt-5-mini → OpenRouter)
- Intercepts SDK network calls via a global fetch hook
- Injects routing headers and metadata into outgoing requests
- Handles subagent model inheritance for the Task tool

2. Cloudflare Worker (worker/)
A stateless proxy that translates between API formats. It:
- Routes requests to Anthropic (passthrough) or OpenRouter (with translation)
- Converts Anthropic Messages API ↔ OpenRouter Chat Completions format
- Handles streaming (SSE) translation with tool call assembly
- Enforces server tool policies (MCP, web search, etc.)

3. Demo Application (claude-agent-demo/)
A full-stack Next.js reference implementation of the Claude Agent SDK featuring:
- 12-model selection UI (3 Claude + 9 OpenRouter models)
- Streaming chat with real-time tool execution visualization
- Image upload support, extended thinking controls, session management
- Transcript recording and permission policies

Table of Contents
1. Repo…