Chat Completions

Method and path

POST/v1/chat/completions

Base URL https://api.relayvia.dev/v1. Send the key as Authorization: Bearer sk-....

Common parameters

Requests are forwarded in the original format, so the original API's parameters work unless the next section says otherwise. This table lists the common ones; see the official reference for the rest.

Differences from the original API

• Server-side stored state cannot be referenced: a non-null previous_response_id, conversation, container, file_id, vector_store_ids, item_reference or cached_content, or a top-level file, returns 400 unsupported_parameter with param naming the field. Your own tool schemas, tool-call arguments and metadata are not checked. store is always treated as false.
• tools[] only accepts function and custom tools. Tools that the model maker runs and bills separately (web search, code execution, file search and similar), web_search_options and mcp_servers return 400 unsupported_parameter.
• user, safety_identifier and prompt_cache_key are scoped to your account before forwarding, so prompt caches and user ids are never shared with other accounts.
• Chunks are forwarded as they arrive. A : keepalive comment line is sent after every 15 seconds without data; SSE clients ignore it. The usage chunk is only sent if you set stream_options.include_usage. The model field always shows the name you sent.
• A non-streaming request with no response within 95 seconds returns 500 upstream_timeout; use streaming for long outputs. Or send the header X-Robi-Keepalive: 1: if there is no response within 30 seconds you get a 200 right away and a space every 15 seconds until the JSON arrives, and a later failure arrives as an error object in the body.
• n must be a positive integer, otherwise 400 invalid_request. The reservation and the charge cover every choice.

Request examples

curl https://api.relayvia.dev/v1/chat/completions \
  -H "Authorization: Bearer sk-..." \
  -H "Content-Type: application/json" \
  -d '{"model":"gpt-5.5","messages":[{"role":"user","content":"Hello!"}]}'

from openai import OpenAI

client = OpenAI(base_url="https://api.relayvia.dev/v1", api_key="sk-...")
resp = client.chat.completions.create(model="gpt-5.5", messages=[{"role": "user", "content": "Hello!"}])
print(resp.choices[0].message.content)

import OpenAI from "openai";

const client = new OpenAI({ baseURL: "https://api.relayvia.dev/v1", apiKey: "sk-..." });
const resp = await client.chat.completions.create({
  model: "gpt-5.5",
  messages: [{ role: "user", content: "Hello!" }],
});
console.log(resp.choices[0].message.content);

Response and streaming examples

{
  "id": "chatcmpl-abc123",
  "object": "chat.completion",
  "created": 1793750400,
  "model": "gpt-5.5",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "Hello! How can I help?"
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 9,
    "completion_tokens": 8,
    "total_tokens": 17
  }
}

data: {"id":"chatcmpl-abc123","object":"chat.completion.chunk","model":"gpt-5.5","choices":[{"index":0,"delta":{"role":"assistant","content":"Hello!"}}]}

: keepalive

data: {"id":"chatcmpl-abc123","object":"chat.completion.chunk","model":"gpt-5.5","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

data: [DONE]

Errors this endpoint returns

Every code, its fixed message and what to do are on the error codes page.