{"schema":"postcutoff/event@1","as_of":"2026-11-13T13:49:00+01:00","url":"https://postcutoff.com/e/2026-09-28-claude-sonnet-5-5/","md":"https://postcutoff.com/e/2026-09-28-claude-sonnet-5-5/index.md","disclosure":{"written_by":"AI agents (Claude Opus 5.5 in Claude Code)","editor":"human editor","policy":"https://postcutoff.com/about/"},"license":null,"id":"2026-09-28-claude-sonnet-5-5","date":"2026-09-28","date_precision":"day","short_title":"Anthropic releases Claude Sonnet 5.5","deck":"30% faster, Opus-5.5-level scores on several benchmarks at $2/$10","takeaway":"Six days after Opus 5.5, Anthropic released Claude Sonnet 5.5 (claude-sonnet-5-5) on September 28, 2026.","category":"model-release","category_label":"Model releases","importance":4,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":[{"n":1,"title":"Introducing Claude Sonnet 5.5 (Anthropic)","url":"https://www.anthropic.com/claude-sonnet-5-5","type":"official","group":"primary","domain":"anthropic.com"},{"n":2,"title":"Claude Sonnet 5.5 System Card","url":"https://www.anthropic.com/claude-sonnet-5-5-system-card","type":"paper","group":"primary","domain":"anthropic.com"},{"n":3,"title":"Sonnet 5.5 migration guide","url":"https://platform.claude.com/docs/en/models/sonnet-5-5/migration-guide","type":"docs","group":"primary","domain":"platform.claude.com"},{"n":4,"title":"TechCrunch: Anthropic releases Sonnet 5.5","url":"https://techcrunch.com/2026/09/28/anthropic-releases-sonnet-5-5-which-it-calls-a-significantly-cheaper-faster-work-partner/","type":"press","group":"press","domain":"techcrunch.com"},{"n":5,"title":"VentureBeat: Sonnet 5.5 with 30% cost reduction per task","url":"https://venturebeat.com/technology/anthropic-launches-claude-sonnet-5-5-with-30-cost-reduction-per-task-due-to-faster-speeds-and-fewer-tool-calls","type":"press","group":"press","domain":"venturebeat.com"},{"n":6,"title":"SiliconANGLE: Sonnet 5.5 runs 30% faster","url":"https://siliconangle.com/2026/09/28/anthropic-debuts-claude-sonnet-5-5-running-30-faster-than-the-previous-generation-ai-model/","type":"press","group":"press","domain":"siliconangle.com"},{"n":7,"title":"Thurrott: Anthropic Releases Claude Sonnet 5.5","url":"https://www.thurrott.com/a-i/anthropic/342139/anthropic-releases-claude-sonnet-5-5","type":"press","group":"press","domain":"thurrott.com"},{"n":8,"title":"Artificial Analysis: Claude Sonnet 5.5","url":"https://artificialanalysis.ai/articles/claude-sonnet-5-5","type":"press","group":"press","domain":"artificialanalysis.ai"},{"n":9,"title":"Introducing Claude Sonnet 5.5 (official video)","url":"https://www.youtube.com/watch?v=s5nkj-L2vAw","type":"video","group":"reactions","domain":"youtube.com"},{"n":10,"title":"Simon Willison: Claude Sonnet 5.5","url":"https://simonwillison.net/2026/Sep/28/claude-sonnet-5-5/","type":"discussion","group":"reactions","domain":"simonwillison.net"}],"official":3,"filed":"2026-09-29","updated":"2026-09-29","orgs":["Anthropic"],"title":"Anthropic releases Claude Sonnet 5.5 — 30% faster, Opus-5.5-level scores on several benchmarks at $2/$10","summary":"Six days after Opus 5.5, Anthropic released Claude Sonnet 5.5 (`claude-sonnet-5-5`) on September 28, 2026. It keeps Sonnet 5's price ($2/$10 per million tokens) but runs 30%+ faster and costs up to 30% less per task because it uses fewer tokens and tool calls. It nearly matches Opus 5.5 on GDPval-AA and OSWorld and beats it on Terminal-Bench 4.0.","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'","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"],"key_numbers":[],"tags":["llm","claude","sonnet","claude-5-5","agentic-coding","pricing"],"science":null,"body_md":"## What happened\n\nAnthropic 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\".\n\nBenchmarks from the announcement page (Sonnet 5.5 / Sonnet 5 / Opus 5.5):\n\n| Benchmark | Sonnet 5.5 | Sonnet 5 | Opus 5.5 |\n|---|---|---|---|\n| Terminal-Bench 4.0 | 70.6% | 10.3% | 66.4% |\n| FrontierCode 1.1 (High) | 46.2% | 42.4% | 54.4% |\n| CursorBench 4.0 | 55.5% | 34.1% | 57.8% |\n| GDPval-AA v2.1 | 1844 | 1449 | 1846 |\n| AA-Briefcase v1.1 | 1811 | 1359 | 1822 |\n| OSWorld 2.1 | 80.1% | 57.0% | 81.8% |\n\nPrice 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.\n\n## Why it matters\n\nSonnet 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.","disputed":[],"related":[{"id":"2026-09-22-claude-opus-5-5","url":"https://postcutoff.com/e/2026-09-22-claude-opus-5-5/","date":"2026-09-22","date_precision":"day","short_title":"Anthropic releases Claude Opus 5.5","deck":"Fable-5.1-level performance at $4/$20, first model of the Claude 5.5 family","takeaway":"Opus 5.5 continues the 2026 pattern of Mythos-class capability moving down into cheaper tiers.","category":"model-release","category_label":"Model releases","importance":5,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":36,"official":16,"filed":"2026-09-29","updated":"2026-10-18","orgs":["Anthropic"]},{"id":"2026-06-30-claude-sonnet-5","url":"https://postcutoff.com/e/2026-06-30-claude-sonnet-5/","date":"2026-06-30","date_precision":"day","short_title":"Anthropic releases Claude Sonnet 5, \"the most agentic Sonnet yet\"","deck":null,"takeaway":"It moved Opus-4.8-class agentic ability to the default free tier just weeks after Mythos-class models reached the public.","category":"model-release","category_label":"Model releases","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":5,"official":3,"filed":"2026-09-29","updated":"2026-09-29","orgs":["Anthropic"]}],"people":[{"id":"simon-willison","name":"Simon Willison","url":"https://postcutoff.com/person/simon-willison/"}],"posts":[{"id":"2026-10-07-claudeai-sonnet-5-5-cache-reads-halved","title":"Claude: 'One more thing', cache reads on Sonnet 5.5 halved to $0.10 per million tokens","url":"https://postcutoff.com/p/2026-10-07-claudeai-sonnet-5-5-cache-reads-halved/"},{"id":"2026-09-28-claudeai-introducing-sonnet-5-5","title":"Introducing Claude Sonnet 5.5","url":"https://postcutoff.com/p/2026-09-28-claudeai-introducing-sonnet-5-5/"}],"videos":[{"id":"siyabuilt-sonnet-5-5-vs-gpt-6-astra-what-you-look-like-x","title":"\"Build what you think you look like\": Claude Sonnet 5.5 vs GPT-6 Astra","url":"https://postcutoff.com/v/siyabuilt-sonnet-5-5-vs-gpt-6-astra-what-you-look-like-x/"},{"id":"claude-introducing-sonnet-5-5","title":"Introducing Claude Sonnet 5.5","url":"https://postcutoff.com/v/claude-introducing-sonnet-5-5/"},{"id":"claudeai-sonnet-5-5-fall-foliage-simulator-x","title":"Fall foliage simulator made with Sonnet 5 vs Sonnet 5.5 (official @claudeai launch-thread video)","url":"https://postcutoff.com/v/claudeai-sonnet-5-5-fall-foliage-simulator-x/"},{"id":"ai-search-gemini-4-gpt-6-1-dots-claude-sonnet-5-5-ai-news","title":"Gemini 4, GPT 6.1, Dots, Claude Sonnet 5.5, Ideogram 4.5, Flux 3: AI NEWS","url":"https://postcutoff.com/v/ai-search-gemini-4-gpt-6-1-dots-claude-sonnet-5-5-ai-news/"},{"id":"devteamdrew-claude-effort-levels-visualization-x","title":"A visualization of every Claude effort level, made with Opus 5.5 and Sonnet 5.5","url":"https://postcutoff.com/v/devteamdrew-claude-effort-levels-visualization-x/"},{"id":"two-minute-papers-the-billion-dollar-ai-advantage-is-disappearing","title":"The Billion Dollar AI Advantage Is Disappearing","url":"https://postcutoff.com/v/two-minute-papers-the-billion-dollar-ai-advantage-is-disappearing/"},{"id":"chase-ai-the-sol-6-1-benchmarks-are-stupid-so-i-tested-it-vs-sonnet-5","title":"The Sol 6.1 Benchmarks Are STUPID, So I Tested It vs Sonnet 5.5","url":"https://postcutoff.com/v/chase-ai-the-sol-6-1-benchmarks-are-stupid-so-i-tested-it-vs-sonnet-5/"},{"id":"yt-bijan-bowen-claude-sonnet-5-5-is-insane-seriously-th","title":"Claude Sonnet 5.5 Is INSANE – Seriously, This Model Is Ridiculous!","url":"https://postcutoff.com/v/yt-bijan-bowen-claude-sonnet-5-5-is-insane-seriously-th/"},{"id":"nate-herk-sonnet-5-5-vs-opus-5-5","title":"I Tested Sonnet 5.5 vs Opus 5.5. What You Need to Know.","url":"https://postcutoff.com/v/nate-herk-sonnet-5-5-vs-opus-5-5/"},{"id":"yt-worldofai-huge-fable-5-5-leak-sonnet-5-5-is-insane","title":"HUGE Fable 5.5 LEAK, Sonnet 5.5 IS INSANE, GPT 6.1, Qwen 4.0, Kimi K3.1 & More! 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