Flatkey REST API: Endpoints, Auth, and Request Format

The Flatkey API is a REST API that is fully compatible with the OpenAI API specification. Every request goes to https://router.flatkey.ai/v1 — the same base URL for all endpoints, providers, and models. Authentication uses a Bearer token in the Authorization header.

Base URL

https://router.flatkey.ai/v1

Authentication

All requests must include your Flatkey API key as a Bearer token:

Authorization: Bearer sk-fk-your-api-key

Generate your API key in the console. See Authentication for full details.

Request format

All requests use HTTPS
Request bodies must be JSON (Content-Type: application/json)
Responses are JSON (or SSE for streaming)

Available endpoints

Endpoint	Method	Description
`/v1/chat/completions`	POST	Chat and text generation (OpenAI-compatible)
`/v1/responses`	POST	OpenAI Responses API (stateful multi-turn)
`/v1/embeddings`	POST	Text embeddings
`/v1/images/generations`	POST	Image generation
`/v1/models`	GET	List available models

OpenAI SDK compatibility

Because the API is OpenAI-compatible, you can use the official OpenAI Python or Node.js SDK with no changes to the request code — just set base_url:

from openai import OpenAI

client = OpenAI(
    api_key="sk-fk-your-api-key",
    base_url="https://router.flatkey.ai/v1",
)

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: "sk-fk-your-api-key",
  baseURL: "https://router.flatkey.ai/v1",
});

Versioning

Flatkey uses the same versioning scheme as the OpenAI API. The /v1 path prefix is stable. When new OpenAI API versions are released, Flatkey adds support while maintaining backward compatibility with /v1.

Rate limits

Rate limits are applied per API key. If you exceed the limit, you receive a 429 Too Many Requests response. Contact support@flatkey.ai if you need higher rate limits for production workloads.

Supported content types

Content type	Used for
`application/json`	All request bodies and responses
`text/event-stream`	Streaming responses (when `stream: true`)

​Base URL

​Authentication

​Request format

​Available endpoints

​OpenAI SDK compatibility

​Versioning

​Rate limits

​Supported content types