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AnthropicClaude 5 familyCurrentReasoning modelReleased 22 Sep 2026

Claude Opus 5.5

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

Model idclaude-opus-5-5

Price$4 in, $20 out per 1M tokens

Checked29 September 2026

Knows up to June 2026

1,795events after its cutoff

81 historic, 409 major. 136 days of news.

It launched on 22 September 2026, already missing 372 of them.

Five things it has never heard of

How to call it

7 ways to use Claude Opus 5.5, with the model id each provider expects.

Providers, model ids, endpoints and docs for Claude Opus 5.5
ProviderModel idEndpointDocs
Anthropic API (Claude API) claude-opus-5-5 https://api.anthropic.com/v1/messages platform.claude.com
AWS Bedrock (Messages API / Mantle) anthropic.claude-opus-5-5 platform.claude.com
Google Cloud Vertex AI claude-opus-5-5 platform.claude.com
Microsoft Foundry (Azure) claude-opus-5-5 platform.claude.com
Claude Platform on AWS claude-opus-5-5 platform.claude.com
OpenRouter anthropic/claude-opus-5.5 openrouter.ai
Web app claude.ai

Pricing

Prices for Claude Opus 5.5
Input$4 per 1M tokens
Output$20 per 1M tokens
Cache read$0.20 per 1M tokens

As published: “per 1M tokens (USD); Batch API 50% off”.

Source: platform.claude.com, checked 29 September 2026.

Specs

Input
Text, images and PDF
Output
Text
Context window
1,000,000 tokens
Max output
128,000 tokens
Open weights
No
Licence
Proprietary
Training cutoff
June 2026
Released
22 September 2026
Status
Current
Type
Reasoning model

What stands out

What its maker marketed at launch, and what people found later, each with its source.

  • 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: anthropic.com

  • 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: anthropic.com

  • 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: anthropic.com

  • 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: anthropic.com

  • 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: platform.claude.com

Four assistants, one scale

Each row runs from what the model knows (graphite) through the months between its cutoff and its launch (hatched) to today (pink).

  1. GPT-6 Astra 271 at launch, 1,863 today
  2. Claude Opus 5.5 372 at launch, 1,795 today
  3. Gemini 4 Hydrogen 1,863 at launch, 1,889 today
  4. Grok 4.7 387 at launch, 1,829 today
Show as a table
ModelCutoffReleasedMissing at launchMissing today
GPT-6 AstraApril 20263 September 20262711,863
Claude Opus 5.5June 202622 September 20263721,795
Gemini 4 HydrogenMarch 202612 November 20261,8631,889
Grok 4.7May 202621 September 20263871,829

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.

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: