Anthropic releases Claude Sonnet 5.5
30% faster, Opus-5.5-level scores on several benchmarks at $2/$10
Confirmed
Importance: major (4 of 5)The takeaway
Six days after Opus 5.5, Anthropic released Claude Sonnet 5.5 (claude-sonnet-5-5) on September 28, 2026.
Status
- Claim
Confirmed
- Our reporting
- High confidence
- Importance
- Major (4 of 5)
- Last verified
- 29 September 2026
Your AI and this story
- GPT-6 Astra151 days after its cutoff
- Claude Opus 5.590 days after its cutoff
- Gemini 4 Hydrogen181 days after its cutoff
- Grok 4.7120 days after its cutoff
None of these four assistants can know about it. The closest, Claude Opus 5.5, stops 90 days before it.
Key facts
- Released September 28, 2026; model id claude-sonnet-5-5; on Claude Platform, AWS/Bedrock, Google Cloud and Microsoft Foundry
- Pricing per 1M tokens: $2 input / $10 output; cache reads $0.20; cache writes $2.50 (same as Sonnet 5)
- Terminal-Bench 4.0: 70.6% (Sonnet 5: 10.3%; Opus 5.5: 66.4%)
- GDPval-AA v2.1: 1844 (Opus 5.5: 1846; Sonnet 5: 1449); AA-Briefcase v1.1: 1811
- OSWorld 2.1: 80.1% (Opus 5.5: 81.8%); CursorBench 4.0: 55.5%; FrontierCode 1.1 (High): 46.2%
- Context 1M tokens, max output 128K, adaptive thinking, default effort ‘high’, knowledge cutoff June 2026 (docs comparison table)
- First Sonnet model to beat Pokémon Red working only from screenshots (per press coverage)
- Cyber safeguards similar to Opus 5.5; biology safeguards match Sonnet 5; Haiku 5.5 promised ‘in the coming weeks’
Show 1 more
- Artificial Analysis Intelligence Index: Sonnet 5.5 (max) ranks above GPT-6 Astra (max) and behind only Opus 5.5 (max), but uses the most tokens of the three
What happened
Anthropic shipped Claude Sonnet 5.5 on September 28, 2026 as the “faster, lower-cost complement” to Opus 5.5 (released Sept 22). Anthropic says it is strongest at well-scoped everyday tasks, fixing bugs, and making polished documents, slides and spreadsheets. It also has “a strong eye for design”.
Benchmarks from the announcement page (Sonnet 5.5 / Sonnet 5 / Opus 5.5):
| Benchmark | Sonnet 5.5 | Sonnet 5 | Opus 5.5 |
|---|---|---|---|
| Terminal-Bench 4.0 | 70.6% | 10.3% | 66.4% |
| FrontierCode 1.1 (High) | 46.2% | 42.4% | 54.4% |
| CursorBench 4.0 | 55.5% | 34.1% | 57.8% |
| GDPval-AA v2.1 | 1844 | 1449 | 1846 |
| AA-Briefcase v1.1 | 1811 | 1359 | 1822 |
| OSWorld 2.1 | 80.1% | 57.0% | 81.8% |
Price is unchanged from Sonnet 5 ($2/$10). Anthropic says the per-task savings come from using fewer tokens and tool calls. New anti-distillation classifiers and “preserved thinking” also apply. YouTube reviewers quickly ran Sonnet 5.5 vs Opus 5.5 comparisons, and several argued Sonnet 5.5 is the better value.
Why it matters
Sonnet 5.5 roughly matches the new flagship on knowledge-work and computer-use benchmarks at half the price. That squeezes the value of the Opus tier within a week of its launch and continues the 2026 price war with OpenAI’s GPT-6 Sol and Luna.
Sources
10 sources from 9 sites. Numbers match the chips in the text.
10 sources: 3 primary, 5 press, 2 reactions
Primary
- Introducing Claude Sonnet 5.5 (Anthropic)anthropic.com, official
- Claude Sonnet 5.5 System Cardanthropic.com, paper
- Sonnet 5.5 migration guideplatform.claude.com, docs
Press
- TechCrunch: Anthropic releases Sonnet 5.5techcrunch.com, press
- VentureBeat: Sonnet 5.5 with 30% cost reduction per taskventurebeat.com, press
- SiliconANGLE: Sonnet 5.5 runs 30% fastersiliconangle.com, press
- Thurrott: Anthropic Releases Claude Sonnet 5.5thurrott.com, press
- Artificial Analysis: Claude Sonnet 5.5artificialanalysis.ai, press
Reactions
- Introducing Claude Sonnet 5.5 (official video)youtube.com, video
- Simon Willison: Claude Sonnet 5.5simonwillison.net, discussion
Changes
- Added Artificial Analysis ranking and Simon Willison’s notes
- Filed
