API Reference | Aion Labs Docs

Authentication

All endpoints except GET /v1/models require an API key.

Authorization: Bearer YOUR_API_KEY

The Api-Key YOUR_API_KEY header prefix is also accepted. Keys are issued and revoked in the dashboard.

Errors

All errors share the same envelope:

{
  "error": {
    "message": "Human-readable description",
    "type": "<error_type>"
  }
}

HTTP status	type	Cause
400	invalid_request_error	Unknown model, malformed request, or provider validation failure
400	configuration_error	Server-side provider misconfiguration
429	rate_limit_error	Usage limit exceeded for your account
502	provider_error	Upstream provider returned an error

GET /v1/models

Returns the catalog of available models. No authentication required.

Response

{
  "models": [
    {
      "id": "aion-labs/aion-2.0",
      "name": "AionLabs: Aion 2.0",
      "description": "...",
      "date": "2025-12-21",
      "context_length": 131072,
      "max_completion_tokens": 32768,
      "is_moderated": false,
      "architecture": { "modality": "text->text" },
      "pricing": {
        "prompt": "0.0000008",
        "completion": "0.0000016",
        "input_cache_read": "0.0000002"
      }
    }
  ]
}

Pricing fields are per-token. input_cache_read is only present on models with cache pricing.

POST /v1/chat/completions

OpenAI-compatible chat completions. Supports streaming and tool calls.

Request body

Field	Type	Required	Description
model	string	Yes	Model ID. See Models.
messages	array	Yes	Conversation history. See message object below.
temperature	float	No	Sampling temperature.
max_tokens	integer	No	Maximum completion tokens (≥ 1).
stop	string[]	No	Stop sequences.
stream	boolean	No	Stream response as SSE. Default: false.
tools	array	No	Tool definitions in OpenAI format.
reasoning_split	boolean	No	Split <think> reasoning into a separate reasoning field. Defaults on for reasoning models.
metadata	object	No	Arbitrary key-value pairs attached to the request.

Message object

Field	Type	Required	Description
role	string	Yes	system, user, assistant, or tool
content	string or parts	No	Message text, or a list of {"type", "text"} content parts.
tool_calls	array	No	Tool calls returned by the model.
tool_call_id	string	No	ID of the tool call being answered (role tool messages).

Response (non-streaming)

{
  "id": "chatcmpl_abc123",
  "object": "chat.completion",
  "created": 1700000000,
  "model": "aion-labs/aion-2.0",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "Hello! How can I help?"
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 12,
    "completion_tokens": 8,
    "total_tokens": 20,
    "prompt_tokens_details": {
      "cached_tokens": 0
    }
  }
}

When reasoning_split is active, the message gains a reasoning field and content contains only the response text:

{
  "message": {
    "role": "assistant",
    "reasoning": "Let me think through this...",
    "content": "The answer is 42."
  }
}

Response (streaming)

When stream: true, the endpoint returns text/event-stream. Each event is a JSON delta, terminated by data: [DONE]:

data: {"id":"chatcmpl_abc123","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"role":"assistant","content":"Hello"},"finish_reason":null}]}

data: {"id":"chatcmpl_abc123","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"content":" world"},"finish_reason":null}]}

data: [DONE]

POST /v1/responses

Alternative completion endpoint modelled on the OpenAI Responses API shape. Accepts the same model set and supports streaming.

Request body

Field	Type	Required	Description
model	string	Yes	Model ID.
input	string or array	One of	Prompt string, or a list of {"role", "content"} message objects. Mutually exclusive with messages.
messages	array	One of	Chat history in the same format as /v1/chat/completions. Mutually exclusive with input.
temperature	float	No	Sampling temperature.
max_output_tokens	integer	No	Maximum completion tokens (≥ 1).
stream	boolean	No	Stream as SSE. Default: false.
reasoning_split	boolean	No	Split reasoning into a separate content item.
metadata	object	No	Arbitrary metadata.

When using input as a list, each item's content may be a string or a list of {"type": "input_text", "text": "..."} parts.

Response (non-streaming)

{
  "id": "resp_abc123",
  "object": "response",
  "created_at": 1700000000,
  "model": "aion-labs/aion-2.0",
  "status": "completed",
  "output": [
    {
      "id": "msg_xyz",
      "type": "message",
      "status": "completed",
      "role": "assistant",
      "content": [
        { "type": "output_text", "text": "Hello! How can I help?" }
      ]
    }
  ],
  "usage": {
    "input_tokens": 12,
    "output_tokens": 8,
    "total_tokens": 20,
    "input_tokens_details": {
      "cached_tokens": 0
    }
  }
}

When reasoning_split is active, a reasoning item is prepended to content:

"content": [
  { "type": "reasoning", "text": "Let me think through this..." },
  { "type": "output_text", "text": "The answer is 42." }
]