respan-gateway

Key features

• Any client, any model
  OpenAI Chat Completions, OpenAI Responses, Anthropic Messages and Gemini API clients can all call any model, with streaming, tools, images and reasoning translated.

• Multimodal
  Realtime voice across vendors (an OpenAI Realtime client talks to Gemini Live, and back), plus images, speech, transcription, embeddings and video through OpenAI's or Gemini's APIs, to any vendor that has them.

• MCP tools for every model
  Put MCP servers or built-in tool vendors behind the gateway, from web search to code sandboxes. It runs their tools inside chat requests, so a plain chat call can use them, whatever the client or model.

• Traffic control
  Named routes, globs and provider/model; fallback, retries, cheapest or fastest; and hedged requests that race a slow call against a second provider.

• Observability
  A live request log with cost, latency and tokens for every call, and traces in Respan, where span-02 analyzes how your agents behave.

• Best-in-class performance
  0.07 ms of added latency, 56,000 requests per second and 31 MB of memory in our benchmarks: about 3× the throughput of the next fastest gateway we tested.

• Write your own plugin in minutes
  Every feature above is a plugin, built on the same public Rust API you can use: one trait with four hooks. Start from the plugin guide or an example such as guardrails, PII masking or billing.

Quickstart

1. Install

pip install respan-gateway

Or cargo install respan-gateway, or a GitHub release.

2. Run it with your keys

export OPENAI_API_KEY=sk-...
respan-gateway

No config file needed: every vendor whose key is set becomes a provider.

3. Call any model from any SDK

from anthropic import Anthropic

client = Anthropic(base_url="http://localhost:8080", api_key="unused")
reply = client.messages.create(
    model="gpt-6-luna", max_tokens=256,
    messages=[{"role": "user", "content": "Hello from the Anthropic SDK"}])
print(reply.content[0].text)

The web UI is at localhost:8080/ui/. Next: configuration and MCP tools.

Other ways to run it

• Python, in-process — Run the gateway inside your Python app, with no server.
• Embed in Rust — Mount the gateway in your own Rust service.
• Docker — docker run -p 8080:8080 -e OPENAI_API_KEY -e RESPAN_CLIENT_KEYS=<a key of yours> ghcr.io/respanai/respan-gateway on any container host; listening beyond localhost, it needs a client key.

Performance

Configuration

You don't need a config file to start. When you want more, run respan-gateway init for a commented gateway.toml. One file sets up keys, providers, traffic control, tools and tracing:

client_keys = [{ name = "app", key = "env:APP_KEY" }]   # who may call the gateway

[providers.openai]                      # a built-in vendor: just add a key
vendor = "openai"
key = "env:OPENAI_API_KEY"

[providers.anthropic]
vendor = "anthropic"
key = "env:ANTHROPIC_API_KEY"

[providers.local]                       # any OpenAI-compatible endpoint
formats = ["openai-chat"]
base_url = "http://localhost:8000/v1"

[routes.smart]                          # clients ask for "model": "smart"
to = ["anthropic/claude-haiku-5-5", "openai/gpt-6-luna"]
hedge = "800ms"                         # race the second if the first is slow

[tools.search]                          # web search as MCP tools
vendor = "linkup"
key = "env:LINKUP_API_KEY"

[plugins.tool_loop]                     # every model can use them
servers = ["search"]

[plugins.respan]                        # trace every call in Respan
key = "env:RESPAN_API_KEY"

respan-gateway check validates it, and --watch or SIGHUP reloads it without a restart. Without client keys, the gateway answers only on loopback and refuses to start on a public address.

Reference: configuration · vendors · tool vendors · MCP and tools · gateway.example.toml

Supported API formats

Call the gateway in any format on the left, and it reaches every provider on the right, translating between them.

	Your code calls	It can reach
Chat	OpenAI Chat Completions OpenAI Responses Anthropic Messages Gemini API	any chat model, whichever of the four formats it speaks
Realtime voice	OpenAI Realtime Gemini Live	OpenAI ⇄ Gemini voice; Mistral for transcription
Images	OpenAI Images Gemini Images
Speech, transcription	OpenAI Speech OpenAI Transcriptions
Embeddings	OpenAI Embeddings
Video	OpenAI Videos Gemini Veo	Google Veo
Decisions	Respan Decisions TypeSafe System One
Tools	MCP	your MCP servers and tool vendors
Anything else	A vendor's own API	Relayed to that vendor untouched

Each vendor's formats are in vendors, and the translation details in each format's README: chat, media, realtime and decisions.

Plugins

Everything the gateway does is a plugin on one public Rust API.

Models · 16 providers and any compatible endpoint, each reachable from any client format. All vendors →

Tools · any MCP server, plus built-in tools for search, browsing, code, documents and memory, usable from any model. All tool vendors →

Traffic control · named routes, fallback, retries, hedged requests, and the cheapest or fastest provider.

Observability · a live request log, the cost of every call, and traces in Respan.

Your framework · anything with a base URL. Guides for the OpenAI SDK, Anthropic SDK, Google GenAI, Vercel AI SDK, LangChain, Pydantic AI, Pi, OpenCode and more.

Your own plugin · start from the plugin guide or an example: guardrails, PII masking, billing, an LLM judge.

Built in: routing · tool-loop · mcp-router · pricing · respan · responses · credentials

Community

Contributions are welcome. CONTRIBUTING.md covers the architecture, building and tests, and a new vendor is usually one file. Start with a good first issue, ask in Discussions or Discord, and report security issues as SECURITY.md describes.

Roadmap: what we're building next is in issues. Missing a vendor, format or feature? Ask for it.

Want it managed? Respan runs the gateway for you, with dashboards, evals and span-02.

License

Dual-licensed under MIT or Apache-2.0, at your option.