# API overview

> Every endpoint the gateway exposes, which format it speaks, and what it returns.

_Source: https://aiprimetech.io/docs/api-reference/overview/ · Home > Docs > API reference_

Three endpoints. Two request formats. One key.

| Method | Path | Format | Purpose |
|---|---|---|---|
| POST | `/v1/messages` | Anthropic Messages | Chat completion, Anthropic envelope |
| POST | `/v1/chat/completions` | OpenAI Chat Completions | Chat completion, OpenAI envelope |
| GET | `/v1/models` | OpenAI-style list | Model ids your key can call |

A machine-readable description is published at [/openapi.json](/openapi.json), and a plain-text summary of the whole site at [/llms.txt](/llms.txt) and [/llms-full.txt](/llms-full.txt).


## Choosing an endpoint

They front the **same models at the same price**. Pick by what your client already emits — do not translate formats yourself.

| Endpoint | Auth header | Response shape | Streaming |
|---|---|---|---|
| `/v1/messages` | `x-api-key` or Bearer | `content[]` array + `usage` | SSE, `content_block_delta` events |
| `/v1/chat/completions` | Bearer | `choices[].message.content` | SSE, `choices[].delta.content` chunks |

> The streaming shapes differ and are not interchangeable. A client written for `choices[].delta.content` will read nothing at all from a Messages stream. See [Streaming](/docs/api-reference/streaming/).


## Common headers

| Header | Applies to | Notes |
|---|---|---|
| `content-type: application/json` | both POSTs | Required |
| `x-api-key` | Messages | Anthropic style |
| `Authorization: Bearer` | both | OpenAI style; also accepted by Messages |
| `anthropic-version: 2023-06-01` | Messages | Set automatically by Anthropic SDKs |
| `accept: text/event-stream` | both | Set by SDKs when `stream` is true |

- [Messages](https://aiprimetech.io/docs/api-reference/messages/) — Anthropic format reference
- [Chat Completions](https://aiprimetech.io/docs/api-reference/chat-completions/) — OpenAI format reference
- [Models endpoint](https://aiprimetech.io/docs/api-reference/models-endpoint/) — Discovering ids
- [Errors](https://aiprimetech.io/docs/api-reference/errors/) — Status codes


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_ClaudeAPIKey.dev is an independently operated, Anthropic-compatible API gateway. Not affiliated with Anthropic._