Core

Chat completions

The OpenAI chat completions endpoint for Claude, GPT and Gemini. The parameters that it accepts, the response, images, and the parameters that it refuses.

POST /v1/chat/completions

The request and the response have the OpenAI format. We do not change the field names, so an OpenAI client works without a change. Claude, GPT and Gemini models work on this endpoint. See Supported endpoints.

Parameters

Field	Notes
`model`	Necessary. A model id. See Models
`messages`	Necessary. Roles `system`, `user`, `assistant` and `tool`. `content` is a string, or a list of parts for images
`max_tokens`	The maximum number of output tokens. The default is 16,000 (4,096 on the starter balance) and the maximum is 128,000. Without `max_tokens`, a low balance lowers the default to what the balance can hold, but never below 1,024. We hold the cost of this number of tokens from your balance until the request completes
`max_completion_tokens`	The newer OpenAI name for `max_tokens`. Send one of the two. If you send the two with different values, you get a `400` error
`temperature`, `top_p`, `stop`, `seed`	We send them to the model. The ranges are the OpenAI ranges
`frequency_penalty`, `presence_penalty`	We send them to the model
`stream`, `stream_options`	See Streams
`tools`, `tool_choice`, `parallel_tool_calls`	See Tool calls
`response_format`	See Structured output
`reasoning_effort`, `verbosity`	We send them to the model. See Models
`logprobs`, `top_logprobs`	We send them to the model
`prompt_cache_key`	See Prompt cache

The response

{
  "id": "chatcmpl-8f2a1c",
  "object": "chat.completion",
  "created": 1791331200,
  "model": "claude-haiku-4-5-20251001",
  "choices": [
    {
      "index": 0,
      "message": { "role": "assistant", "content": "The capital of Kenya is Nairobi." },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 21,
    "completion_tokens": 8,
    "total_tokens": 29,
    "prompt_tokens_details": { "cached_tokens": 0 }
  },
  "kontinent": { "request_id": "req_8f2a1c", "cost_micros": 13, "cost_usd": 0.000013, "list_price_usd": 0.000061, "saved_usd": 0.000048 }
}

The kontinent block is not part of the OpenAI format. An OpenAI client ignores it. It shows the cost of the request, the cost at the official price, and the difference. See Supported endpoints.

finish_reason comes from the model:

Value	Meaning
`stop`	The model completed its answer
`length`	The model used all of `max_tokens`
`tool_calls`	The model asks you to run a function
`error`	The stream stopped after it started. See Reliability

Conversations

Send all of the conversation in each request. We keep no state between requests.

Python

messages = [{"role": "system", "content": "Answer in one sentence."}]

while True:
    messages.append({"role": "user", "content": input("> ")})
    reply = client.chat.completions.create(model="claude-haiku-4-5-20251001", messages=messages)
    text = reply.choices[0].message.content
    messages.append({"role": "assistant", "content": text})
    print(text)

Images

Some models can read images. To send an image, make content a list of parts, as in the OpenAI format:

{
  "model": "claude-sonnet-5-5",
  "messages": [
    {
      "role": "user",
      "content": [
        { "type": "text", "text": "What is in this picture?" },
        { "type": "image_url", "image_url": { "url": "https://example.com/photo.jpg" } }
      ]
    }
  ]
}

Before you send an image, look at input_modalities in GET /v1/models. A model that reads images shows ["text", "image"]. If you send an image to a model that shows only ["text"], you get a 400 error that names messages. We do not charge for that request.

We charge for an image on the token count that the model gives. The usage block of the response shows that count.

What this endpoint does not do

n larger than 1 does not work. Send the request more than one time. For the other parameters and endpoints that we do not have, see Not supported yet.