Messages (Anthropic-compatible)

POST https://gateway.acog.tessarac.com/v1/messages

The Anthropic Messages API. Send exactly what you would send to Anthropic, including the anthropic-version header. ACOG routes by model: a Claude model goes to whichever of your Anthropic, Bedrock or Vertex connections declares it, and a GPT or Gemini model is translated.

Example

import os
from anthropic import Anthropic

client = Anthropic(
    base_url="https://gateway.acog.tessarac.com",
    # The gateway key is sent as Authorization: Bearer. Use auth_token, not api_key.
    auth_token=os.environ["ACOG_API_KEY"],
)

message = client.messages.create(
    model="claude-sonnet-4-5",
    max_tokens=512,
    messages=[{"role": "user", "content": "Explain prompt caching in one paragraph."}],
)
print(message.content[0].text)

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  baseURL: "https://gateway.acog.tessarac.com",
  authToken: process.env.ACOG_API_KEY,
});

const message = await client.messages.create({
  model: "claude-sonnet-4-5",
  max_tokens: 512,
  messages: [{ role: "user", content: "Explain prompt caching in one paragraph." }],
});

curl -s https://gateway.acog.tessarac.com/v1/messages \
  -H "Authorization: Bearer $ACOG_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "Content-Type: application/json" \
  -d '{"model": "claude-sonnet-4-5", "max_tokens": 512, "messages": [{"role": "user", "content": "Hello"}]}'

If your code sets ANTHROPIC_API_KEY in the environment, the Anthropic SDK sends it as x-api-key. ACOG ignores a provider key there, so the request fails with 401. Unset it, or pass the gateway key explicitly as shown.

What is supported

Feature	Supported
System prompts, multi-turn conversations	Yes
Tools, tool use and tool results	Yes
Images and documents (base64 or URL)	Yes. For Bedrock and Vertex, ACOG fetches URL sources and sends them inline (up to 5 MB, 10-second fetch).
Prompt caching (cache_control)	Yes. ACOG also adds cache breakpoints you did not set; see Caching.
Extended thinking	Yes. If the serving model rejects it, ACOG retries without it and sets x-acog-thinking-stripped: true.
anthropic-beta	Forwarded. If the serving platform rejects a beta value, ACOG retries without it and names it in x-acog-beta-stripped.
Streaming	Yes. See Streaming.
model: "auto" and <model>:batch	Yes. See Auto mode and Batches.

Token counting (/v1/messages/count_tokens), Message Batches (/v1/messages/batches) and the Files API are not part of the compatible route. Call them on the native route, https://gateway.acog.tessarac.com/anthropic. See Native provider routes.

Translation to other providers

A GPT model (OpenAI, Azure OpenAI or a custom endpoint) or a Gemini model is translated from and to the Messages format, including streamed responses. Translation is strict: a field with no faithful equivalent is refused with 422 translation_unsupported.

The response

The response is an Anthropic message object. The header x-acog-resolved-model names the model that answered.

When a budget passes 50, 80 or 90% of its limit, ACOG appends a one-time notice after the model’s reply and sets x-acog-budget-notice. See Budgets.