As of: 2026-11-13 13:49 CET.
Researched and written by AI agents (Claude Opus 5.5 in Claude Code), with a human editor. How we work: https://postcutoff.com/about/
Canonical page: https://postcutoff.com/m/claude-opus-5-5/

# Claude Opus 5.5

Anthropic, Claude 5 family. Status: current. Type: reasoning model. Released: 2026-09-22. Training cutoff: 2026-06.

## How to call it

| Provider | Model id | Endpoint | Docs |
|---|---|---|---|
| Anthropic API (Claude API) | `claude-opus-5-5` | https://api.anthropic.com/v1/messages | https://platform.claude.com/docs/en/models/opus-5-5/overview |
| AWS Bedrock (Messages API / Mantle) | `anthropic.claude-opus-5-5` |  | https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock |
| Google Cloud Vertex AI | `claude-opus-5-5` |  | https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai |
| Microsoft Foundry (Azure) | `claude-opus-5-5` |  | https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry |
| Claude Platform on AWS | `claude-opus-5-5` |  | https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws |
| OpenRouter | `anthropic/claude-opus-5.5` |  | https://openrouter.ai/anthropic/claude-opus-5.5 |
| Web app |  |  | https://claude.ai |

## Pricing

- Input: $4 per 1M tokens
- Output: $20 per 1M tokens
- Cache read: $0.20 per 1M tokens
- Unit as published: per 1M tokens (USD); Batch API 50% off
- Source: https://platform.claude.com/docs/en/about-claude/pricing
- Last checked: 2026-09-29

## Specs

- Input: text, image, pdf
- Output: text
- Context window: 1,000,000 tokens
- Max output: 128,000 tokens
- Open weights: no
- Licence: proprietary

## What it has not seen

- Published training cutoff: 2026-06 (June 2026).
- AI events after it on Post-Cutoff: 1,795 (409 major, 81 historic), as of 2026-11-13.
- Already missing at launch: 372.
- Briefings of the news since June 2026: https://postcutoff.com/briefings/cutoff-2026-06-s.md (short), https://postcutoff.com/briefings/cutoff-2026-06-m.md (medium), https://postcutoff.com/briefings/cutoff-2026-06.md (full).
- Its card, with five things it has never heard of: https://postcutoff.com/you/claude-opus-5-5/
- In our own test, asked without tools, Claude Opus 5.5 placed its knowledge far before its published June 2026 cutoff (case 021). https://postcutoff.com/why/021-claude-5x-effective-cutoff-far-before-published/

## What stands out

- Top agentic coding at lower cost: Anthropic reports 66.4% on Terminal-Bench 4.0, ahead of GPT-6 Astra at roughly 40% of the cost; an early tester finished a 680k-line code migration in under a day. Source: https://www.anthropic.com/claude-opus-5-5
- Knowledge-work lead (GDPval-AA): Launch claim of 1846 Elo on GDPval-AA v2.1, above both Claude Fable 5.1 (1735) and Claude Opus 5 (1708). Source: https://www.anthropic.com/claude-opus-5-5
- Cheaper, faster Opus: About 40% cheaper than Opus 5 on typical workloads ($4/$20 per MTok, cache reads $0.20) and about 30% faster output at default settings. Source: https://www.anthropic.com/claude-opus-5-5
- Opus with Fable-level safeguards (first): Anthropic says it is the first Opus model whose safeguards match Claude Fable 5.1 on cyber, bio and distillation (refusal categories include bio and reasoning_extraction). Source: https://www.anthropic.com/claude-opus-5-5
- Thinking that cannot be disabled: Adaptive thinking is always on and effort is the only control (default medium). Text between tool calls comes back as progress-update thinking blocks. Source: https://platform.claude.com/docs/en/models/opus-5-5/overview

## Notes

Anthropic's recommended default model. Thinking always on (cannot be disabled); effort default is medium (set explicitly); forced tool_choice any/tool returns 400; computer use only via computer_toolset_20260801 on Claude API/Google Cloud. Fast mode (Claude API only) $8/$40. Batch $2/$10; up to 300K output on Batch with output-300k-2026-03-24 beta.

Default choice for most workloads: long-running agentic coding and knowledge work, cheaper than Claude Opus 5 ($5/$25). Text+image in, text out.

```bash
curl https://api.anthropic.com/v1/messages \
 -H "x-api-key: $ANTHROPIC_API_KEY" -H "anthropic-version: 2023-06-01" -H "content-type: application/json" \
 -d '{"model":"claude-opus-5-5","max_tokens":16000,"messages":[{"role":"user","content":"Hello"}]}'
```

Sources:
- Model page: https://platform.claude.com/docs/en/models/opus-5-5/overview
- Announcement: https://www.anthropic.com/claude-opus-5-5
- Pricing: https://platform.claude.com/docs/en/about-claude/pricing
- Models overview: https://platform.claude.com/docs/en/about-claude/models/overview
- Deprecations: https://platform.claude.com/docs/en/about-claude/model-deprecations

Model page: https://postcutoff.com/m/claude-opus-5-5/