API reference

Celeris implements the OpenAI chat-completions wire format. For usage examples and parameter guidance, see Making requests.

Base URL

https://inference.celeris.ai/<model>/v1

Placeholder	Values today
model	celeris-1

The model request-body field must match the <model> path segment.

Authentication

All endpoints require a bearer key (details):

Authorization: Bearer ck_...

POST /chat/completions

Create a chat completion. Responses can return as one JSON body or as an SSE stream (details).

Request body

Field	Type	Required	Notes
model	string	yes	Must equal the model in the URL path, e.g. celeris-1.
messages	array	yes	OpenAI message objects (role ∈ system | user | assistant | tool). content is a string, or an array of content parts: {"type": "text", "text": ...} and {"type": "image_url", "image_url": {"url": "data:<media-type>;base64,..."}}. Attach as many image_url parts as you need, using inline data: URLs only; see Image input. Prompt tokens plus max_tokens must be at most 131,072.
max_tokens	integer	recommended	Completion-token limit. Any positive integer, and prompt tokens plus max_tokens must be at most 131,072. Defaults to 2048 when omitted. A zero or negative value, or a value that would exceed the context window, is rejected. Size it for the expected response; see parameter guidance.
temperature	number	no	0 recommended for structured tasks.
top_p	number	no	Standard nucleus sampling.
seed	integer	no	Reproducible sampling when combined with temperature: 0.
stop	string | array	no	Stop sequences.
n	integer	no	Number of choices.
tools	array	no	Function/tool definitions in the OpenAI tools schema. When the model calls one, the reply's message.tool_calls carries the function name and JSON arguments, and finish_reason is tool_calls. Send the result back as a tool message to continue.
tool_choice	string | object	no	auto (the default, where the model decides), none (never call), required (directs the model to call one of tools), or {"type": "function", "function": {"name": "..."}} to direct a specific function. required and named forcing apply to non-streaming requests; confirm the reply carries tool_calls. See Tool calling.
response_format	object	no	Constrain non-streaming /chat/completions output to JSON: {"type": "json_object"}, or {"type": "json_schema", "json_schema": {"name": "...", "schema": {...}}} to validate against a schema. See JSON mode.
chat_template_kwargs	object	no	Template controls. {"enable_thinking": true} makes the model reason before answering (off by default); where the reasoning is separated it is returned on message.reasoning, apart from message.content. See Reasoning.
include_reasoning	boolean	no	Chat-only (the Responses API has no equivalent). Defaults to true; set false and the reasoning field comes back null instead of carrying the working. It does not suppress a working that was not separated for that request. See Reasoning for the response shape and the post-tool-result exception.
presence_penalty, frequency_penalty	number	no	Standard penalties.
stream	boolean	no	Set true for SSE chunks.
stream_options.include_usage	boolean	no	With streaming, set true to receive the final exact-usage block.

The effective input limit is 131,072 - max_tokens. Requests over the token limit return 400; request bodies over the endpoint's 64 MiB byte limit return 413.

Response body

{
  "id": "chatcmpl-9f2e41c0",
  "object": "chat.completion",
  "created": 1751673600,
  "model": "celeris-1",
  "choices": [
    {
      "index": 0,
      "message": {"role": "assistant", "content": "Positive"},
      "finish_reason": "stop"
    }
  ],
  "usage": {"prompt_tokens": 27, "completion_tokens": 2, "total_tokens": 29}
}

finish_reason is stop (natural completion or stop sequence) or length (hit max_tokens).

When the request enables thinking (chat_template_kwargs: {"enable_thinking": true}), message may also carry a reasoning string alongside content; while streaming it arrives as delta.reasoning chunks ahead of delta.content. Reasoning tokens count as completion tokens in usage. See Reasoning for when it is present and how to detect it.

POST /v1/responses

Create a model response with the OpenAI Responses API, an alternative to /chat/completions that takes a single input instead of a messages array. It returns one JSON body or an SSE stream (details) and reports token usage. Each request is self-contained: send the full input on every call.

Request body

Field	Type	Required	Notes
model	string	yes	Must equal the model in the URL path, e.g. celeris-1.
input	string | array	yes	A prompt string, or an array of OpenAI input messages (role ∈ system | user | assistant). A message's content is a string, or an array of input parts: {"type": "input_text", "text": ...} and {"type": "input_image", "image_url": "data:<media-type>;base64,...", "detail": "auto"}. The chat text / image_url spellings are rejected here, and detail is required; attach as many input_image parts as you need. See Image input.
instructions	string	no	System-level guidance applied ahead of input.
max_output_tokens	integer	no	Output-token limit; any positive integer, bounded by the 131,072-token context window, with the same rejection rules as max_tokens above, but not its 2048 default. When omitted, Responses uses the context window remaining after the rendered input; set it explicitly to bound latency and cost.
temperature	number	no	0 recommended for structured tasks.
top_p	number	no	Standard nucleus sampling.
chat_template_kwargs	object	no	{"enable_thinking": true} makes the model reason before answering (off by default); where the reasoning is separated it is returned as an output item of type: "reasoning", ahead of the message item. See Reasoning.
stream	boolean	no	Set true for Responses SSE events.

Response body

{
  "id": "resp_9f2e41c0",
  "object": "response",
  "created_at": 1751673600,
  "status": "completed",
  "model": "celeris-1",
  "output": [
    {
      "id": "msg_1a2b3c4d",
      "type": "message",
      "status": "completed",
      "role": "assistant",
      "content": [{"type": "output_text", "text": "Positive", "annotations": []}]
    }
  ],
  "usage": {"input_tokens": 27, "output_tokens": 2, "total_tokens": 29}
}

The generated text is at the type: "message" item's content[0].text (the OpenAI SDK also exposes it as response.output_text). When thinking is enabled and the reasoning is separated, an output item of type: "reasoning" precedes that message item; take the answer from the message item, never the reasoning. See Reasoning on the Responses API for that item's shape and how to detect it. When streaming, the event sequence ends with a response.completed event.

GET /v1/models

Lists the model served at this base URL, in the standard OpenAI list shape:

curl https://inference.celeris.ai/celeris-1/v1/models \
  -H "Authorization: Bearer $CELERIS_API_KEY"

Retrieve a single model by id with GET /v1/models/celeris-1 to get that model's metadata in the standard OpenAI object shape:

curl https://inference.celeris.ai/celeris-1/v1/models/celeris-1 \
  -H "Authorization: Bearer $CELERIS_API_KEY"

Request headers

Header	Meaning
Authorization	Required on every call: Bearer ck_... (details).
Content-Type	application/json on POST.
X-Client-Trace-Id	Optional caller-supplied trace ID. Echoed on responses so you can correlate failures with application logs and support cases.

Response headers

Header	Meaning
Server-Timing	Service processing duration until the response headers are ready, in milliseconds. For streaming this precedes the first token. See Measuring latency.
X-Client-Trace-Id	Your request's trace id, echoed back if you sent one.
Access-Control-Allow-Origin: *	Browser calls are supported from any origin (details).
Access-Control-Expose-Headers	Lets browser code read Server-Timing and the trace-id headers cross-origin.
Retry-After	On 429: seconds to wait before retrying.

Errors

See Errors for causes, response bodies, and handling guidance. API errors use {"error": {message, type, code}}; use error.code when a status has more than one possible cause.

Status	error.code	Reference
400	Varies by validation error	400 Bad Request
401	invalid_api_key	401 Unauthorized
402	insufficient_quota	402 Payment Required
404	not_found	404 Not Found
413	payload_too_large	413 Payload Too Large
429	rate_limit_exceeded / service_busy	429 Too Many Requests
502	upstream_error	502 Bad Gateway
503	service_unavailable	503 Service Unavailable