Migrating from another gateway

The swap

Coming from OpenAI directly, or from a gateway that speaks the same format, the diff is three lines.

- baseURL: "https://api.openai.com/v1",
- apiKey:  process.env.OPENAI_API_KEY,
- model:   "gpt-4o",
+ baseURL: "https://api.multigrid.ai/v1",
+ apiKey:  process.env.MULTIGRID_API_KEY,
+ model:   "openai/gpt-4o",

Model ids are the one thing that always needs touching: ours are namespaced vendor/model. GET /models is public, so you can map your ids before you change any code.

What carries over

The request body is OpenAI’s and validation is deliberately shallow — we check that model is a non-empty string and that messages has at least one entry, and let everything else through. A parameter a vendor added last week reaches them untouched rather than being rejected by us for being unfamiliar.

The routing fields are named the same way OpenRouter names them, on purpose: models for a fallback chain and provider: { order, ignore, allow_fallbacks, sort } for provider preferences. A config carried over keeps working rather than being silently ignored, which would change your bill without changing your code. See provider preferences.

What is different

• Responses carry a multigrid object. Model, provider, attempts and exact cost. Additive — clients that do not know about it ignore it.
• Errors use OpenAI’s envelope with our codes. { error: { message, type, code, request_id } }. Existing error handling keeps parsing; the code values are ours. See the error reference.
• Streams end with our terminal chunk. Usage and cost arrive on a final chunk before data: [DONE], so a client that stops reading at the first finish_reason will miss the numbers but not the answer.
• HTTP-Referer and X-Title are read. OpenRouter’s two attribution headers land as the referer and title request tags, filterable in Activity and groupable in Analytics like any other tag — so the labels you have been slicing spend by survive the move without touching a call site. An explicit metadata.referer or metadata.title in the body wins over the header. There is no public app leaderboard here for them to feed; they are yours.
• Browser calls work, and the spec is machine-readable. Every /v1 endpoint sends CORS headers and answers preflights, so a client-side integration carries over. The OpenAPI 3.1 document at /api/openapi.json generates clients, Postman collections and mocks.

What we do not implement

Two fields other gateways use are accepted and stripped before the request leaves us: transforms and route. Nothing breaks if they arrive, and nothing happens either — if you were relying on prompt transforms to fit a long context, that work is not being done here.

There is also no stored, versioned routing policy object to migrate to. Routing is expressed per request, or saved as a preset you call by name.

Checklist

• Map every model id against GET /models.
• Confirm we hold a route for each one: GET /models/{vendor}/{model}/endpoints lists the providers, in the order they will be tried, with prices.
• Move gateway-specific fields you were sending into metadata or delete them. HTTP-Referer and X-Title can stay as they are.
• Set a spend cap on the new key before you point production at it.
• Run a playground call against each model to confirm we have a working key for its provider on this deployment.