Claude Sonnet 5.5

by September 28, 20261M context128K output

Claude Sonnet 5.5 is the speed and cost tier of Anthropic’s Claude 5.5 family, a faster and lower-cost alternative to Opus 5.5 for well-scoped everyday work. It reads text and images, calls tools, and uses adaptive thinking with configurable effort, with strong results in bug fixing, agentic and computer-use tasks, and polished documents. Its 1M-token context window and 128K-token maximum output cover long conversations, large documents, and multi-file code work.

Claude Sonnet 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@sonnet-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@sonnet-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@sonnet-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@sonnet-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@sonnet-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@sonnet-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@sonnet-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.