Claude Sonnet 5.5
Claude Sonnet 5.5 is Anthropic's mid-tier model, which the company describes as its balance of speed and intelligence. Released September 28, 2026, it pairs a 1M-token context window with adaptive thinking that defaults to high effort.
Specifications
- Context window
- 1Mabout 750,000 words, or 1,500 pages
- Max output
- 125Ktokens per response
- Input price
- $2per 1M tokens
- Output price
- $10per 1M tokens
- Cached input
- $0.10per 1M tokens
- Weights
- ClosedProprietary
- Parameters
- Undisclosed
- Input types
- Text, Images, PDF
- Output types
- Text
- Reasoning mode
- Yes
- Tool calling
- Yes
- Released
- Sep 28, 2026Current
Standard rates; no surcharge across the 1M-token window. Batch API 50% off. US-only inference adds 1.1x.
What it costs in practice
| Workload | Monthly cost at list price |
|---|---|
| Support chatbot30,000 conversations a month, 2,000 input and 400 output tokens each | $240 |
| Document summaries2,000 documents a month, 12,000 input and 800 output tokens each | $64 |
| Coding agent1,000 tasks a month, 60,000 input and 6,000 output tokens each | $180 |
Standard rates, no caching or batch discounts. Run your own numbers.
Strengths
- Half the per-token price of Claude Opus 5.5
- 1M-token context window and 128K-token output limit
- Up-front thinking can be switched off with the between_tools setting
Trade-offs to weigh
- Non-default temperature, top_p or top_k values return a 400 error
- Forced tool use returns an error
Where it fits
Anthropic positions Claude Sonnet 5.5 for:
Where you can use it
- API
- Claude apps
- Amazon Bedrock
- Google Vertex AI
- Microsoft Azure AI Foundry
- Claude Platform on AWS
- OpenRouter
Alternatives to consider
| Model | Tier | Context | Input / output per 1M | |
|---|---|---|---|---|
| GPT-6.1 SolOpenAI | Advanced | 1.05M | $2 / $10 | Compare |
| Mistral Medium 3.5Mistral AI | Advanced | 256K | $1.50 / $7.50 | Compare |
| Muse Spark 1.3Meta | Advanced | 1M | $1.25 / $4.25 | Compare |
| Gemini 3.8 FlashGoogle | Advanced | 1M | $0.75 / $3.75 | Compare |
Frequently asked questions
How much does Claude Sonnet 5.5 cost?
Claude Sonnet 5.5 lists at $2 per million input tokens and $10 per million output tokens, with cached input at $0.10 (checked October 10, 2026). Standard rates; no surcharge across the 1M-token window. Batch API 50% off. US-only inference adds 1.1x. Confirm current rates on the provider's pricing page before you commit.
What is the context window of Claude Sonnet 5.5?
Claude Sonnet 5.5 accepts up to 1,000,000 tokens of context (about 750,000 words, or 1,500 pages), and it can write up to 125K tokens in a single response. Long prompts cost more and can be slower, so most apps send only what the task needs.
Is Claude Sonnet 5.5 open source?
No. Claude Sonnet 5.5 is a proprietary model from Anthropic; its weights aren't published. You can use it through the Anthropic API and through Claude apps, Amazon Bedrock, Google Vertex AI, Microsoft Azure AI Foundry, Claude Platform on AWS, OpenRouter.
What is Claude Sonnet 5.5 best for?
Anthropic positions Claude Sonnet 5.5 for coding, agents, chat, writing. It accepts text, images, pdf as input, has a reasoning (thinking) mode and supports tool calling. Test it on a sample of your own tasks before you choose it for production.
Sources
- platform.claude.com/docs/en/models/sonnet-5-5/overview
- platform.claude.com/docs/en/about-claude/pricing
- platform.claude.com/docs/en/models/overview.md
- platform.claude.com/docs/en/build-with-claude/pdf-support
- computeprices.com/models/claude-sonnet-5-5
Facts checked against these pages on October 10, 2026. Spot an error? Tell us.
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