Claude Opus 5.5

by September 21, 20261M context128K output

Claude Opus 5.5 is Anthropic’s most capable Opus release, built for agent systems that run for hours, large-codebase engineering, and analysis that spans many documents. It reads text and images, uses tools, and exposes configurable effort and extended thinking, so a team can trade latency against depth on a per-request basis. Its 1M-token context window and 128K-token maximum output suit codebase-wide refactors, research synthesis, and long transcript work.

Claude Opus 5.5 is served through Runware's compatible endpoints, which take another provider's request format. Point the SDK you already use at Runware by changing the base URL and the API key, and set model to anthropic:claude@opus-5.5.

Requests and responses keep the provider's format, so its reference documents every parameter.

Endpoint	Format
`/v1/chat/completions`	OpenAI Chat Completions
`/v1/messages`	Anthropic Messages

Chat Completions

cURL

curl -X POST https://api.runware.ai/v1/chat/completions \
  -H "Authorization: Bearer $RUNWARE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic:claude@opus-5.5",
    "messages": [{"role": "user", "content": "What is the capital of France?"}]
  }'

Python

from openai import OpenAI

client = OpenAI(
    api_key="your_runware_api_key",
    base_url="https://api.runware.ai/v1",
)

response = client.chat.completions.create(
    model="anthropic:claude@opus-5.5",
    messages=[{"role": "user", "content": "What is the capital of France?"}],
)

print(response.choices[0].message.content)

TypeScript

import OpenAI from 'openai';

const client = new OpenAI({
  apiKey: 'your_runware_api_key',
  baseURL: 'https://api.runware.ai/v1',
});

const response = await client.chat.completions.create({
  model: 'anthropic:claude@opus-5.5',
  messages: [{ role: 'user', content: 'What is the capital of France?' }],
});

console.log(response.choices[0].message.content);

Compatible APIs covers streaming, tool calling and how the endpoint differs from OpenAI, and the OpenAI API reference lists every parameter.

Messages

cURL

curl -X POST https://api.runware.ai/v1/messages \
  -H "Authorization: Bearer $RUNWARE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic:claude@opus-5.5",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "What is the capital of France?"}]
  }'

Python

from anthropic import Anthropic

client = Anthropic(
    auth_token="your_runware_api_key",
    base_url="https://api.runware.ai",
)

message = client.messages.create(
    model="anthropic:claude@opus-5.5",
    max_tokens=1024,
    messages=[{"role": "user", "content": "What is the capital of France?"}],
)

print(message.content[0].text)

TypeScript

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

const client = new Anthropic({
  authToken: 'your_runware_api_key',
  baseURL: 'https://api.runware.ai',
});

const message = await client.messages.create({
  model: 'anthropic:claude@opus-5.5',
  max_tokens: 1024,
  messages: [{ role: 'user', content: 'What is the capital of France?' }],
});

console.log(message.content[0].text);

Compatible APIs covers how the Anthropic SDKs authenticate against Runware, and the Claude API reference lists every parameter.