# Claude Sonnet 5.5

> Anthropic's Sonnet model balancing speed and intelligence, for well-scoped everyday work such as features and bug fixes.

## Key facts

- Model author: Anthropic
- Input: $2.00 per 1M tokens
- Output: $10.00 per 1M tokens
- Cached input: $0.10 per 1M tokens
- Context window: 1,000,000 tokens
- Maximum output: 128,000 tokens
- Input modalities: image, text
- Output modalities: text
- Capabilities: reasoning, tools, vision
- Released: 2026-09-28
- Knowledge cutoff: Jun 2026
- Model IDs: `anthropic/claude-sonnet-5-5`
- Model page: https://www.realrelay.ai/model/anthropic/claude-sonnet-5-5

## Overview

Claude Sonnet 5.5 is a Sonnet-class model from Anthropic designed to balance speed and intelligence. It uses adaptive thinking, so it can reason more on hard steps and less on easy ones, and it supports tool calling and image input. It suits well-scoped everyday work such as building features and fixing bugs.

Claude Sonnet 5.5 has a 1M-token context window and can generate up to 128K output tokens. It accepts text and image input and returns text output. It was released on September 28, 2026. Its knowledge cutoff is June 2026.

## Capabilities

Claude Sonnet 5.5 supports reasoning, tool calling and image understanding. It accepts text and image as input and produces text as output.

Adaptive thinking keeps responses quick on simple requests while leaving room for deeper reasoning when a task needs it. With a 1M-token window and tool calling, it can read a project and edit files through tools.

## Pricing

Claude Sonnet 5.5 costs $2.00 per 1M input tokens and $10.00 per 1M output tokens. Cache reads are $0.10 per 1M tokens.

Claude Sonnet 5.5 is available through RealRelay's OpenAI-compatible API.

## Use cases

Use Claude Sonnet 5.5 for everyday engineering tasks such as building a feature, fixing a bug or writing tests, calling tools to read and edit files inside a 1M-token window.

Its balance of speed and intelligence also suits interactive assistants that answer questions about screenshots, documents and data in a single request.

## Call it

OpenAI-compatible chat completions:

```bash
curl https://www.realrelay.ai/v1/chat/completions \
  -H "Authorization: Bearer $REALRELAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "anthropic/claude-sonnet-5-5", "messages": [{"role": "user", "content": "Hello"}]}'
```

## FAQ

### What is Claude Sonnet 5.5?

Claude Sonnet 5.5 is a Sonnet-class model from Anthropic designed to balance speed and intelligence. It supports reasoning, tool calling and image understanding and accepts text and image input.

### How much does Claude Sonnet 5.5 cost?

Claude Sonnet 5.5 costs $2.00 per 1M input tokens and $10.00 per 1M output tokens, with cache reads at $0.10 per 1M tokens.

### What is the context window of Claude Sonnet 5.5?

Claude Sonnet 5.5 has a 1M-token context window and can generate up to 128K tokens in a single response.

### What inputs and outputs does Claude Sonnet 5.5 support?

Claude Sonnet 5.5 accepts text and image input and returns text output.

### Does Claude Sonnet 5.5 support tool calling?

Yes. Claude Sonnet 5.5 supports tool calling, so it can call functions you define and use the results in multi-step tasks. It also supports reasoning and image understanding.

### When was Claude Sonnet 5.5 released?

Claude Sonnet 5.5 was released on September 28, 2026. Its knowledge cutoff is June 2026.

### How do I call Claude Sonnet 5.5 via the API?

Call Claude Sonnet 5.5 through RealRelay's OpenAI-compatible API using the model ID anthropic/claude-sonnet-5-5.