Frontier flagship models
Claude Sonnet 5.5
Made by Anthropic
Anthropic's faster, lower-cost everyday model — the second release in the Claude 5.5 family.
What it is
Claude Sonnet 5.5, announced 28 September 2026, is the second model in the Claude 5.5 family and a complement to Opus 5.5: where Opus 5.5 is built for complex work requiring sustained judgment, Sonnet 5.5 is aimed at well-scoped everyday tasks — fixing bugs, and creating documents, slides and spreadsheets.
Anthropic's launch post reports 70.6% on Terminal-Bench 4.0 agentic coding (up from 10.3% for Sonnet 5), two points below Opus 5.5 on GDPval-AA, and outputs generated 30%+ faster than Sonnet 5. It is also the first Sonnet model to beat Pokémon Red working only from screenshots. Those are the maker's own figures; check independent leaderboards for a specific task.
API pricing matches Sonnet 5 — $2 per million input tokens, $10 per million output tokens, $0.20 per million cache-read tokens — but Anthropic's testing says the model needs fewer tokens for the same work, costing up to 30% less per task than its predecessor. It is the first Sonnet model to launch with cyber safeguards and fallbacks like those on the lab's most capable models; its biology safeguards match Sonnet 5's.
Anthropic says Claude Haiku 5.5, built for high-volume and cost-sensitive applications, will join the Claude 5.5 family in the coming weeks.
The first Sonnet model to launch with cyber safeguards like those on the lab's most capable models, per the announcement; heavier use on Claude plans follows usage-window limits.
Published price
- API — input$2 per 1M tokens
- API — output$10 per 1M tokens
- API — cache reads$0.20 per 1M tokens
- Claude FreeChat on web, desktop and mobile; usage-window limits apply$0
- Claude Pro$17/month (annual) or $20/month
- Claude MaxFrom $100/month
API prices come from the launch announcement; consumer plan prices are for Claude.ai overall, and model access on each plan follows usage limits rather than a fixed assignment.
Source: Anthropic's launch announcement · Last checked 28 September 2026
Benchmarks
The published figures for Claude Sonnet 5.5, copied exactly as their sources give them and checked 17 September 2026. Each one names the test, who ran it and when, and says when the number comes from the maker rather than an independent tester.
- Artificial Analysis Intelligence Index v4.3.256 — 3rd of 216 models
combined score across ten reasoning and knowledge tests · tested: max with fallback
Artificial Analysis · 28 September 2026 · independent
Measured at 141.9 tokens per second output speed.
Figures copied from the sources above, checked 17 September 2026.
Where to read today's numbers
Scores move, so these are the boards that keep them current.
- LMArena leaderboardIndependent
Ranks models by blind head-to-head votes from the public. Good for a feel for general quality, weak on specialist work.
- Artificial AnalysisIndependent
Independent testing of quality, speed and price per million tokens across hosted models.
- Vals AI benchmarksIndependent
Independent evaluations on real professional tasks — law, finance, tax, medicine — rather than vendor demos.
How it performs, in my experience
Anthropic's faster, lower-cost complement to Opus 5.5, announced 28 September 2026, aimed at well-scoped everyday tasks — fixing bugs and producing documents, slides and spreadsheets. The launch post reports 70.6% on Terminal-Bench 4.0 agentic coding (up from 10.3% for Sonnet 5), two points below Opus 5.5 on GDPval-AA, and outputs generated 30%+ faster than Sonnet 5; benchmark figures are the maker's own, so check independent leaderboards for a specific task.
Prompting it from this site
Can't be run from here
This site has no Claude wired up — the models it prompts run through OpenAI's and Google's endpoints. Use Claude.ai or Anthropic's API instead.
Use it for
- Everyday coding and bug fixes
- Polished documents, slides and spreadsheets
- High-volume work that doesn't need Opus 5.5's sustained judgment