{"schema":"postcutoff/event@1","as_of":"2026-11-13T13:49:00+01:00","url":"https://postcutoff.com/e/2026-07-24-claude-opus-5/","md":"https://postcutoff.com/e/2026-07-24-claude-opus-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":"2026-07-24-claude-opus-5","date":"2026-07-24","date_precision":"day","short_title":"Anthropic releases Claude Opus 5","deck":"Near-Fable-5 intelligence at half the price","takeaway":"Claude Opus 5 (claude-opus-5) launched on July 24, 2026 at $5/$25 per million tokens.","category":"model-release","category_label":"Model releases","importance":4,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":[{"n":1,"title":"Introducing Claude Opus 5 (Anthropic)","url":"https://www.anthropic.com/news/claude-opus-5","type":"official","group":"primary","domain":"anthropic.com"},{"n":2,"title":"Claude Opus 5 System Card (PDF)","url":"https://www-cdn.anthropic.com/c5fbac3f0b1280a933ebd26d3cb8bb9f5bdeaf48/Claude%20Opus%205%20System%20Card.pdf","type":"paper","group":"primary","domain":"www-cdn.anthropic.com"},{"n":3,"title":"Claude Opus 5 docs overview","url":"https://platform.claude.com/docs/en/models/opus-5/overview","type":"docs","group":"primary","domain":"platform.claude.com"},{"n":4,"title":"Irregular: Assessing Claude Opus 5 against offensive security benchmarks (July 24)","url":"https://www.irregular.com/research/assessing-claude-opus-5-against-offensive-security-benchmarks","type":"official","group":"primary","domain":"irregular.com"},{"n":5,"title":"TechCrunch: Anthropic launches Opus 5","url":"https://techcrunch.com/2026/07/24/anthropic-launches-opus-5/","type":"press","group":"press","domain":"techcrunch.com"},{"n":6,"title":"Axios: Anthropic releases new model, Opus 5","url":"https://www.axios.com/2026/07/24/anthropic-releases-new-model-opus-5","type":"press","group":"press","domain":"axios.com"},{"n":7,"title":"9to5Mac: Anthropic upgrades Claude with Opus 5","url":"https://9to5mac.com/2026/07/24/anthropic-upgrades-claude-with-new-opus-5-model-details-here/","type":"press","group":"press","domain":"9to5mac.com"},{"n":8,"title":"Simon Willison: Introducing Claude Opus 5","url":"https://simonwillison.net/2026/Jul/24/introducing-claude-opus-5/","type":"discussion","group":"reactions","domain":"simonwillison.net"},{"n":9,"title":"MindStudio: Why is Opus 5 getting bad reviews despite top benchmarks?","url":"https://www.mindstudio.ai/blog/anthropic-claude-opus-5-trust-crisis","type":"discussion","group":"reactions","domain":"mindstudio.ai"}],"official":4,"filed":"2026-09-29","updated":"2026-10-29","orgs":["Anthropic"],"title":"Anthropic releases Claude Opus 5 — near-Fable-5 intelligence at half the price","summary":"Claude Opus 5 (`claude-opus-5`) launched on July 24, 2026 at $5/$25 per million tokens. Anthropic said it comes close to Fable 5's frontier intelligence at half the price and sets new highs on Frontier-Bench v0.1 and GDPval-AA. Developers soon complained it was verbose and prone to over-engineering, which Opus 5.5 set out to fix two months later.","key_facts":["Released July 24, 2026; model id claude-opus-5; $5 input / $25 output per 1M tokens; fast mode 2x base price for ~2.5x speed","Context 1M tokens (default and max), 128K output; thinking on by default","Frontier-Bench v0.1: more than doubles Opus 4.8's performance; CursorBench 3.2 within 0.5% of Fable 5 at half the cost (Anthropic)","Anthropic reports an ARC-AGI-3 score 3x higher than the next-best model (exact number not captured)","Default model on Claude Max; cybersecurity classifiers intervene 85% less often than on Fable 5","Anthropic called it its 'most aligned model to date' on the behavioral audit","Irregular (July 24): on a nine-challenge CyScenarioBench subset with deployment mitigations disabled, Opus 5 averaged a 33.7% solve rate vs Opus 4.8 24.4%, Sonnet 5 3.3% and Claude Mythos 5 47.0%; most attempts did not reach the scenario objective"],"key_numbers":[],"tags":["llm","claude","opus","agentic-coding","computer-use"],"science":null,"body_md":"## What happened\n\nOpus 5 upgrades Opus 4.8 with gains in agentic coding, computer use and long-horizon knowledge work. It is much better at verifying its own work and iterating until it succeeds. New API betas arrived with it: changing tools mid-conversation and automatic fallback to alternative models. It remained behind Mythos 5 on cyber exploitation and biology research.\n\nReception was mixed. Commentators such as MindStudio reported developer complaints that it was verbose, turned small fixes into large rewrites, and flagged trivial issues as urgent.\n\n## Why it matters\n\nOpus 5 brought most of Fable 5's capability to half the price. Its reception problems explain why Opus 5.5's launch messaging stressed clear, concise communication.","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":"2026-06-09-claude-fable-5-mythos-5","url":"https://postcutoff.com/e/2026-06-09-claude-fable-5-mythos-5/","date":"2026-06-09","date_precision":"day","short_title":"Anthropic releases Claude Fable 5 and Claude Mythos 5","deck":"First generally available Mythos-class model","takeaway":"This was the first time the class of model Anthropic had withheld in April (Mythos Preview) became available to the public.","category":"model-release","category_label":"Model releases","importance":5,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":7,"official":5,"filed":"2026-09-29","updated":"2026-09-29","orgs":["Anthropic"]},{"id":"2026-05-28-claude-opus-4-8","url":"https://postcutoff.com/e/2026-05-28-claude-opus-4-8/","date":"2026-05-28","date_precision":"day","short_title":"Anthropic releases Claude Opus 4.8 with cheaper fast mode and Claude Code \"dynamic workflows\"","deck":null,"takeaway":"Opus 4.8 was the last Opus 4.x release and a bridge to the Mythos-class releases in June.","category":"model-release","category_label":"Model releases","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":7,"official":2,"filed":"2026-09-29","updated":"2026-10-11","orgs":["Anthropic"]}],"people":[{"id":"simon-willison","name":"Simon Willison","url":"https://postcutoff.com/person/simon-willison/"}],"posts":[{"id":"2026-08-02-karpathy-lotr-opus-5-threejs","title":"Beyond the pelican test: Opus 5 renders the Lord of the Rings opening in Three.js","url":"https://postcutoff.com/p/2026-08-02-karpathy-lotr-opus-5-threejs/"},{"id":"2026-07-24-claudeai-introducing-opus-5","title":"Introducing Claude Opus 5","url":"https://postcutoff.com/p/2026-07-24-claudeai-introducing-opus-5/"}],"videos":[{"id":"yt-ai-search-claude-opus-5-is-a-freak","title":"Claude Opus 5 is a freak","url":"https://postcutoff.com/v/yt-ai-search-claude-opus-5-is-a-freak/"},{"id":"anshuc-opus-5-24-hour-game-x","title":"A game from one 24-hour Claude Opus 5 session: every pixel and sound built by Claude","url":"https://postcutoff.com/v/anshuc-opus-5-24-hour-game-x/"},{"id":"yt-paul-j-lipsky-anthropic-just-revealed-how-to-prompt-op","title":"Anthropic Just Revealed How to Prompt Opus 5","url":"https://postcutoff.com/v/yt-paul-j-lipsky-anthropic-just-revealed-how-to-prompt-op/"},{"id":"yt-brock-mesarich-ai-fo-i-tested-fable-5-1-vs-fable-5-vs-opus-5","title":"I Tested Fable 5.1 vs Fable 5 vs Opus 5 (Cost/Speed/Design)","url":"https://postcutoff.com/v/yt-brock-mesarich-ai-fo-i-tested-fable-5-1-vs-fable-5-vs-opus-5/"},{"id":"yt-mehul-mohan-new-sonnet-5-5-is-opus-5-level","title":"NEW Sonnet 5.5 Is Opus 5 Level","url":"https://postcutoff.com/v/yt-mehul-mohan-new-sonnet-5-5-is-opus-5-level/"},{"id":"uncanny-fyi-pdoom-claude-opus-5","title":"pdoom — Claude Opus 5","url":"https://postcutoff.com/v/uncanny-fyi-pdoom-claude-opus-5/"},{"id":"uncanny-fyi-2040-agi-claude-opus-5","title":"2040-agi — Claude Opus 5","url":"https://postcutoff.com/v/uncanny-fyi-2040-agi-claude-opus-5/"}],"models":[],"changes":[{"date":"2026-10-29","type":"edit","text":"Added Irregular's CyScenarioBench result (read directly) (news agent)"},{"date":"2026-09-29","type":"filed","text":"Created"}],"provenance":{"agents":[{"model":"Claude Opus 5.5","maker":"Anthropic","tool":"Claude Code"}],"filed":"2026-09-29","run":null,"sources_read":null,"updated":"2026-10-29","human_review":null,"version":{"date":"2026-10-29"}},"gaps":[{"model_id":"gpt-6-astra","name":"GPT-6 Astra","cutoff":"2026-04","days_after":85,"in_training_data":false},{"model_id":"claude-opus-5-5","name":"Claude Opus 5.5","cutoff":"2026-06","days_after":24,"in_training_data":false},{"model_id":"gemini-4-hydrogen","name":"Gemini 4 Hydrogen","cutoff":"2026-03","days_after":115,"in_training_data":false},{"model_id":"grok-4-7","name":"Grok 4.7","cutoff":"2026-05","days_after":54,"in_training_data":false}],"short_url":"https://postcutoff.com/s/anthropic-claude-opus-5"}