Claude Sonnet 5.5 Release Details and Evaluation Steps
Anthropic released Claude Sonnet 5.5 on September 28, 2026. This brief outlines its 1M token context window, supported modalities, and a practical evaluation…
Official Announcement and Availability
Anthropic officially launched Claude Sonnet 5.5, identified by the model ID claude-sonnet-5-5, on September 28, 2026. This date marks the historical event of the release announcement. The source confirms that the model is available through the Claude API, Claude in Amazon Bedrock, Claude Platform on AWS, Claude on Google Cloud, and Claude in Microsoft Foundry.
- Release Date: September 28, 2026
- Model ID: claude-sonnet-5-5
- Provider: Anthropic
Documented Technical Specifications
The verified specifications for Claude Sonnet 5.5 include a context window of 1,000,000 tokens and a maximum output limit of 128,000 tokens. The model accepts both text and image inputs while producing text outputs. The source indicates that open weights are not confirmed for this release. Pricing details are referenced in the official model page but are not specified in the provided facts.
- Context Window: 1,000,000 tokens
- Max Output Tokens: 128,000
- Input Modalities: Text, Image
- Output Modality: Text
Practical Evaluation Procedure
Engineers should evaluate the model by designing controlled tests rather than assuming performance improvements. First, define a set of representative prompts that utilize the full 1,000,000-token context window to validate long-context retention. Second, measure the latency and accuracy of image input processing compared to text-only baselines. Third, compare the output quality against previous internal standards or specific task requirements. Finally, validate that the 128,000-token output limit does not truncate critical responses in your use case. These steps allow for objective measurement without inferring unverified benefits.
- Test long-context retention using 1M token inputs
- Measure image input processing latency
- Compare output accuracy against defined baselines
- Validate output truncation limits at 128k tokens
Artificial Analysis benchmark review
Benchmark review updated on . These scores apply to the linked artifact and recorded methodology; they do not establish the performance of a different runtime or quantized model.
| Measurement | Recorded result | Measured |
|---|---|---|
| Artificial Analysis Intelligence Index (v4.3) ↗ | 56 index_points | 2026-09-29 |
Review the full benchmark provenance and source methodology →
Primary sources
Frequently asked questions
What is the exact release date for Claude Sonnet 5.5?
The official release date recorded in the source facts is September 28, 2026.
Does the source confirm local installation capabilities?
No. The source states that open weights are not confirmed. It does not establish whether local installation is possible or impossible, nor does it specify hosting arrangements beyond the listed cloud platforms.