Model · Anthropic · Text
Claude Opus 5.5
Anthropic's recommended starting point for most workloads — long-running agentic coding and knowledge work, at a lower price than Claude Opus 5. Succeeds Claude Opus 5 as the Opus-tier flagship.
- Modality
- Text
- License
- Proprietary (Proprietary)
- Context window
- 1,000,000 tokens 1M tokens is both the default and the maximum — there is no smaller context variant. Up to 128k output, or 300k on the Batch API with the output-300k beta header.
- Released
- September 22, 2026
- Last verified
- October 28, 2026
- Runs locally
- No
- Also handles
- vision
Strengths
- Anthropic's named default: its models overview says to start with Opus 5.5 for most workloads
- Long-running agentic coding and knowledge work
- Cheaper than Opus 5 ($4/$20 vs $5/$25 per MTok), with cache reads at 5% of the input price
- Much sharper reading of dense charts, diagrams, and screenshots without tools
Weaknesses
- Thinking is always on — `thinking: disabled` or a manual `budget_tokens` returns a 400 error; steer depth with effort instead
- Forced tool use (`tool_choice` of `any` or `tool`) returns a 400 error
- Default effort drops to `medium` (Opus 5 defaulted to `high`), and it thinks more per turn at a given effort — re-run effort sweeps rather than carrying settings over
- Text between tool calls arrives in thinking blocks that are empty at the default display setting, so streamed progress updates go quiet
- The older `computer_20251124` computer-use tool is rejected on the Claude API and Google-managed Google Cloud
- Closed weights — cannot be self-hosted
Try it
| Where | Type | Notes |
|---|---|---|
| Anthropic API | hosted-api | API key required |
| AWS Bedrock | hosted-api | Enterprise / regional |
| Google Vertex AI | hosted-api | GCP integration |
| Claude.ai | product | Claude apps |
Used in solutions
Version history
- Claude Haiku 5.5 Oct 2026
- Claude Sonnet 5.5 Sep 2026
- Claude Opus 5.5 Sep 2026 Current
- Claude Fable 5.1 Sep 2026
- Claude Mythos 5.1 Sep 2026
Official sources
- Model docs docs
- What's new in Opus 5.5 docs
- Models overview docs
Change log
- — Initial entry. Released 2026-09-22 as the Opus-tier flagship, superseding Claude Opus 5; $4/$20 per MTok, 1M-token context, 128k output (300k on Batch with the beta header).
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