Chat Completions (OpenAI-compatible)

POST https://gateway.acog.tessarac.com/v1/chat/completions

The OpenAI Chat Completions API. Send exactly what you would send to OpenAI; ACOG routes by model to whichever of your connections declares it, translating to and from the Anthropic and Gemini APIs when the model is a Claude or Gemini model.

Example

import os
from openai import OpenAI

client = OpenAI(
    base_url="https://gateway.acog.tessarac.com/v1",
    api_key=os.environ["ACOG_API_KEY"],
)

completion = client.chat.completions.create(
    model="claude-haiku-4-5",
    messages=[
        {"role": "system", "content": "You are terse."},
        {"role": "user", "content": "Name three prime numbers."},
    ],
)
print(completion.choices[0].message.content)

curl -s https://gateway.acog.tessarac.com/v1/chat/completions \
  -H "Authorization: Bearer $ACOG_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "gemini-3.5-flash", "messages": [{"role": "user", "content": "Name three prime numbers."}]}'

What is supported

Feature	Supported
System, user, assistant and tool messages	Yes
Tools and function calling, tool results	Yes
Images in user messages (image_url, URL or base64)	Yes. For Bedrock and Vertex, ACOG fetches image URLs and sends them inline (up to 5 MB, 10-second fetch). A failed fetch is a 400, never a silent drop.
Streaming (stream: true)	Yes. See Streaming.
model: "auto"	Yes. See Auto mode.
<model>:batch	Run at batch prices. See Batches.
Audio output	Forwarded to OpenAI-compatible connections; never cached

Translation to other providers

When the model is served by a connection that speaks a different API (Claude on Anthropic, Bedrock or Vertex; Gemini on Vertex), ACOG translates the request and the response, including streamed responses.

Translation is strict by default. A field that has no faithful equivalent in the target API is refused with 422 translation_unsupported rather than silently dropped, so you never get an answer to a different question than the one you asked. An admin can list fields a connection may drop instead.

Translated requests are not stored in the response cache, because the stored reply would be in the target’s format.

The response

The response is an OpenAI chat completion object. model names the model that answered. The header x-acog-resolved-model carries it too, which is useful when you sent auto.

ACOG adds a few response headers of its own, for example x-acog-cache: hit when the reply came from a cache. See Response headers.

Errors

Errors use the envelope {"error": {"type": "…", "message": "…"}}. An error your provider returned is passed through unchanged. See Errors.