proxx

OpenAI-to-Anthropic API proxy that converts OpenAI-compatible requests to Anthropic format and forwards them to a configurable upstream endpoint.

Features

• OpenAI API compatibility — Exposes /v1/chat/completions and /v1/models endpoints
• Automatic format conversion — Translates OpenAI request/response to/from Anthropic format
• Streaming support — Converts non-streaming upstream responses to OpenAI SSE format for clients
• Security headers — Blocks sensitive headers (Referer, Cookie, X-Forwarded-*) from reaching upstream
• Claude-code mimicry — Sets headers to mimic the claude-code CLI tool
• Single binary — No runtime dependencies, just one executable

Use Cases

• Use OpenAI-compatible tools with Anthropic/ZAI API
• Replace Claude API endpoint without modifying client code
• Proxy requests to different Anthropic-compatible providers

Configuration

Create a config.yaml file in the working directory:

port: 8080
upstream_url: "https://api.z.ai/api/anthropic"

• port: Port to listen on (default: 8080)
• upstream_url: Base URL for the Anthropic-compatible upstream API

Building

Standard Go build

go build -o proxx

Requires Go 1.21+ with only gopkg.in/yaml.v3 as an external dependency.

Nix build (reproducible)

nix build

Or run directly from the flake:

nix run .

This uses a reproducible build environment with pinned dependencies.

Nix development shell

nix shell

Provides Go toolchain with gopls and other development tools.

Running

./proxx

The server will start and log:

Starting proxx on :8080, upstream: https://api.z.ai/api/anthropic

API Endpoints

GET /v1/models

Returns a list of available models in OpenAI format.

Example response:

{
  "object": "list",
  "data": [
    {"id": "glm-4.7", "object": "model", "created": 1234567890, "owned_by": "zhipu"},
    {"id": "glm-4.6", "object": "model", "created": 1234567890, "owned_by": "zhipu"}
  ]
}

POST /v1/chat/completions

Accepts OpenAI chat completion format and converts to Anthropic format.

Request headers:

• Authorization: Bearer <api-key> — Required. Extracted and forwarded as x-api-key
• Content-Type: application/json — Required

Request body:

{
  "model": "glm-4.7",
  "messages": [
    {"role": "user", "content": "Hello!"}
  ],
  "stream": false
}

Non-streaming response:

{
  "id": "chatcmpl-abc123",
  "object": "chat.completion",
  "created": 1234567890,
  "model": "glm-4.7",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "Hello! How can I help you today?"
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 10,
    "completion_tokens": 15,
    "total_tokens": 25
  }
}

Streaming response: Returns Server-Sent Events (SSE) in OpenAI format:

data: {"id":"chatcmpl-abc123","object":"chat.completion.chunk","created":1234567890,"model":"glm-4.7","choices":[{"index":0,"delta":{"role":"assistant"},"finish_reason":null}]}

data: {"id":"chatcmpl-abc123","object":"chat.completion.chunk","created":1234567890,"model":"glm-4.7","choices":[{"index":0,"delta":{"content":"Hello"},"finish_reason":null}]}

data: [DONE]

Field Mapping

OpenAI → Anthropic

OpenAI Field	Anthropic Field	Notes
model	model	Direct mapping
messages[]	messages[]	Converted to Anthropic format
system message	system (top-level)	Extracted from messages
temperature	temperature	Direct mapping
max_tokens	max_tokens	Defaults to 32000 if omitted
top_p	top_p	Direct mapping
stop	stop_sequences	Array mapping
tools[]	tools[]	Function tools converted
tool_choice	tool_choice	Enum mapping

Anthropic → OpenAI

Anthropic Field	OpenAI Field	Notes
content[0].text	choices[0].message.content	Text content
content[].tool_use	choices[0].message.tool_calls[]	Tool calls
usage.input_tokens	usage.prompt_tokens	Input tokens
usage.output_tokens	usage.completion_tokens	Output tokens
stop_reason	finish_reason	end_turn → stop, tool_use → tool_calls, max_tokens → length

Claude-Code Mimicry

The proxy sets these headers on all upstream requests to mimic the claude-code CLI:

Header	Value
User-Agent	claude-cli/1.0.18 (pro, cli)
x-api-key	From incoming Authorization: Bearer
x-app	cli
anthropic-version	2023-06-01
anthropic-beta	interleaved-thinking-2025-05-14,prompt-caching-scope-2026-01-05,context-management-2025-06-27
X-Claude-Code-Session-Id	Random UUID generated at startup
content-type	application/json

Security

Blocked Headers

The proxy blocks these headers from being forwarded to upstream:

• Referer — Prevents leaking internal URLs
• Cookie — Prevents leaking session cookies
• Authorization — Already extracted and forwarded as x-api-key
• X-Forwarded-For — Prevents leaking client IP
• X-Real-Ip — Prevents leaking client IP
• X-Forwarded-Host — Prevents leaking internal hostnames

Project Structure

proxx/
├── README.md          # This file
├── main.go           # Entry point, config loading, HTTP server setup
├── handler.go        # HTTP handlers for /v1/chat/completions and /v1/models
├── converter.go      # OpenAI <-> Anthropic format conversion logic
├── types.go          # Request/response struct types
├── config.yaml       # Default configuration file
├── go.mod
└── go.sum

License

See LICENSE file for details.