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Claude Sonnet 5.5
Anthropic · Sonnet
Anthropic released Claude Sonnet 5.5 on September 28, 2026.
Claude Sonnet 5.5 is the Anthropic model launched on September 28, 2026, which Anthropic describes as offering the best combination of speed and intelligence. It has a 1M token context window, 128k max output tokens (300k on the Message Batches API in beta), adaptive thinking with effort defaulting to high, and text and image input. It costs $2 / $10 per million input / output tokens, and on October 7, 2026 Anthropic halved its prompt cache read price to $0.10 per million tokens. It is available on the Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud and Microsoft Foundry, and is Anthropic's recommended upgrade from Claude Sonnet 4.5.
Claude Sonnet 5.5 at a glance
- Released
- API model id
claude-sonnet-5-5- Available on
- Claude APIAmazon BedrockClaude Platform on AWSGoogle CloudMicrosoft Foundry
- Previous model
- Claude Sonnet 5 (June 30, 2026)
- Announcement
- platform.claude.com
What changed from Claude Sonnet 5
Code written for Claude Sonnet 5 can break in five ways: up-front thinking is turned off with the between_tools setting instead of disabled, forced tool use returns an error, thinking blocks are tied to the model and conversation, the older computer_20251124 tool isn't accepted on the Claude API and Google Cloud, and some models are rejected as advisors.
Thinking blocks Sonnet 5.5 produces work only in the account that produced them or a linked account.
New to model names and version numbers? Read how AI labs version their models.
Claude Sonnet 5.5 release timeline
The launch and every later Anthropic release that mentions Claude Sonnet 5.5, oldest first.
- Claude Sonnet 5.5 launch
Launched Claude Sonnet 5.5, a faster, lower-cost complement to Claude Opus 5.5 in the Claude 5.5 family.
Source: Claude Help Center Release Notes - Claude Sonnet 4.5 Deprecation and Sonnet 5.5 Migration
Deprecation of Claude Sonnet 4.5 model (claude-sonnet-4-5-20250929) with retirement on Claude API scheduled for November 30, 2026. Recommended migration to Claude Sonnet 5.5.
Source: Claude Platform Release Notes - Dreams research preview expanded
Dreams (research preview) now supports Claude Opus 5.5, Claude Fable 5.1, and Claude Sonnet 5.5.
Source: Claude Platform Release Notes - Prompt cache price reduction for Claude Sonnet 5.5
We've lowered the price of prompt cache reads on Claude Sonnet 5.5 from $0.20 USD to $0.10 USD per million tokens: 0.05x the base input price instead of 0.1x. Cache writes and all other prices are unchanged.
Source: Claude Platform Release Notes
Claude Sonnet 5.5 FAQ
When was Claude Sonnet 5.5 released?
Anthropic released Claude Sonnet 5.5 on September 28, 2026. The launch entry below links to the official announcement.
Where is Claude Sonnet 5.5 available?
Claude Sonnet 5.5 is available on Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud and Microsoft Foundry. Later availability changes are listed under follow-up releases on this page.
What is the Claude Sonnet 5.5 API model id?
Use claude-sonnet-5-5 in Anthropic's API.
What came before Claude Sonnet 5.5?
Claude Sonnet 5.5 follows Claude Sonnet 5, released on June 30, 2026.
Other Anthropic models
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