Anthropic Messages API

​

When to use it

​

Set up the SDK

import os
from anthropic import Anthropic

client = Anthropic(
    base_url="https://platform.ai.gloo.com/ai/v2/direct/anthropic",
    auth_token=os.environ["GLOO_API_KEY"],
)

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

const client = new Anthropic({
  baseURL: "https://platform.ai.gloo.com/ai/v2/direct/anthropic",
  authToken: process.env.GLOO_API_KEY,
});

​

Send a message

message = client.messages.create(
    model="gloo-anthropic-claude-opus-5.5",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Explain prompt caching in two sentences."}],
)
for block in message.content:
    if block.type == "text":
        print(block.text)

const message = await client.messages.create({
  model: "gloo-anthropic-claude-opus-5.5",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Explain prompt caching in two sentences." }],
});
for (const block of message.content) {
  if (block.type === "text") console.log(block.text);
}

curl https://platform.ai.gloo.com/ai/v2/direct/anthropic/v1/messages \
  -H "Authorization: Bearer $GLOO_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gloo-anthropic-claude-opus-5.5",
    "max_tokens": 1024,
    "messages": [
      { "role": "user", "content": "Explain prompt caching in two sentences." }
    ]
  }'

​

Models

• gloo-anthropic-claude-opus-5.5
• claude-opus-5-5

• Claude only. A model from another provider returns 404 with model_not_available. Use Direct Responses for those models.
• Retired models return an error instead of a replacement. On this endpoint, a retired Claude model ID returns 404 with model_retired, and the message names the model to use instead. Your thinking and effort settings were written for the model you named, so Gloo does not move them to another model for you. (Other direct endpoints serve the replacement; see Model Lifecycle.)

​

Streaming

with client.messages.stream(
    model="gloo-anthropic-claude-opus-5.5",
    max_tokens=16000,
    messages=[{"role": "user", "content": "Write a short story about a lighthouse."}],
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)
    final = stream.get_final_message()

const stream = client.messages.stream({
  model: "gloo-anthropic-claude-opus-5.5",
  max_tokens: 16000,
  messages: [{ role: "user", content: "Write a short story about a lighthouse." }],
});
stream.on("text", (text) => process.stdout.write(text));
const final = await stream.finalMessage();

• Errors before the stream starts are real HTTP errors. Nothing is sent until Claude’s first event arrives, so a request that fails before then gets an HTTP status (429, 529 and so on) that your SDK can retry, never an error inside a 200.
• Errors after the stream starts end the stream with an event: error, as on Anthropic’s API.
• Use streaming for long outputs. A non-streaming request with max_tokens above 21,333 returns 400, the same limit the SDKs apply. Long non-streaming requests can also time out with 504.

​

Thinking and effort

message = client.messages.create(
    model="gloo-anthropic-claude-opus-5.5",
    max_tokens=16000,
    thinking={"type": "adaptive", "display": "summarized"},
    output_config={"effort": "high"},
    messages=[{"role": "user", "content": "How many prime numbers are there below 100?"}],
)
for block in message.content:
    if block.type == "thinking":
        print("Thinking:", block.thinking)
    elif block.type == "text":
        print("Answer:", block.text)

• Adaptive thinking. Claude 5 models, such as Opus 5.5 and Sonnet 5.5, think adaptively. Set the depth with output_config.effort (low, medium, high, xhigh or max).
• Showing the reasoning. On current Claude models, thinking blocks come back with empty text unless you set display: "summarized", which returns a readable summary of the reasoning. With the thinking-display-updates-2026-08-18 beta, display: "updates" returns short progress notes between tool calls instead.
• Multi-turn. You can send the assistant’s turns back as the SDK returns them, thinking blocks included. Gloo doesn’t pass earlier thinking or redacted_thinking blocks to the model; each new turn starts its own reasoning, and tool loops continue as normal. The x-gloo-ignored-params response header lists messages.thinking when this happens.
• max_tokens covers thinking. Thinking tokens count toward max_tokens. If you ask for more than the model’s output limit, Gloo lowers max_tokens to that limit and names the value it used in the x-gloo-adjusted-params response header, for example max_tokens=128000.

​

Tool use

message = client.messages.create(
    model="gloo-anthropic-claude-opus-5.5",
    max_tokens=4096,
    tools=[{"type": "web_search_20250305", "name": "web_search", "max_uses": 3}],
    messages=[{"role": "user", "content": "What changed in the latest Python release?"}],
)

​

Prompt caching

​

What the request can include

• Content blocks: text, images (base64 or URL), documents (base64, plain text, custom content or URL), search results, tool use and tool results, thinking blocks, and web search blocks when the request includes the web search tool. File ID sources are not supported.
• Messages take the user and assistant roles. Put instructions in the top-level system field; messages with the system role return 400.
• metadata: only user_id is used, and Gloo does not pass your value to the model provider as you sent it.

​

Beta features

​

Not available on this endpoint

​

Limits

• Request size: up to 32 MB per request. A larger body returns 413 with request_too_large.
• Concurrent requests: each organization can have a limited number of Messages requests in flight at once. Past that, you get 429 with rate_limit_error and retry-after: 1. The SDKs retry it for you.
• Output length: max_tokens above the model’s output limit is lowered to that limit (see Thinking and effort), except on non-streaming requests: there, max_tokens above 21,333 returns 400 rather than being lowered (see Streaming).

​

Errors

{
  "type": "error",
  "error": {
    "type": "overloaded_error",
    "message": "The model is temporarily unavailable. Retry shortly.",
    "details": {
      "code": "upstream_capacity",
      "retryable": true
    }
  },
  "request_id": "req_..."
}

​

Pricing

​

Related Documentation