{"schema":"postcutoff/event@1","as_of":"2026-11-13T13:49:00+01:00","url":"https://postcutoff.com/e/2026-05-28-claude-opus-4-8/","md":"https://postcutoff.com/e/2026-05-28-claude-opus-4-8/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":"2026-05-28-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":"Claude Opus 4.8 (claude-opus-4-8) launched on May 28, 2026 at the same $5/$25 price as Opus 4.7.","category":"model-release","category_label":"Model releases","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":[{"n":1,"title":"Claude Code docs: model configuration (effort levels and ultracode)","url":"https://code.claude.com/docs/en/model-config","type":"docs","group":"primary","domain":"code.claude.com"},{"n":2,"title":"Introducing Claude Opus 4.8 (Anthropic)","url":"https://www.anthropic.com/news/claude-opus-4-8","type":"official","group":"primary","domain":"anthropic.com"},{"n":3,"title":"Pilot Shell: Ultracode in Claude Code, effort setting explained","url":"https://pilot-shell.com/blog/ultracode","type":"press","group":"press","domain":"pilot-shell.com"},{"n":4,"title":"MacRumors: Opus 4.8 with gains in coding and honesty","url":"https://www.macrumors.com/2026/05/28/anthropic-claude-opus-4-8/","type":"press","group":"press","domain":"macrumors.com"},{"n":5,"title":"Axios: Anthropic releases new model, Opus 4.8","url":"https://www.axios.com/2026/05/28/anthropic-opus-release-mythos","type":"press","group":"press","domain":"axios.com"},{"n":6,"title":"9to5Mac: Anthropic upgrades Claude with Opus 4.8","url":"https://9to5mac.com/2026/05/28/anthropic-upgrades-claude-with-new-opus-4-8-model-heres-whats-new/","type":"press","group":"press","domain":"9to5mac.com"},{"n":7,"title":"Simon Willison: Claude Opus 4.8 — a modest but tangible improvement","url":"https://simonwillison.net/2026/May/28/claude-opus-4-8/","type":"discussion","group":"reactions","domain":"simonwillison.net"}],"official":2,"filed":"2026-09-29","updated":"2026-10-11","orgs":["Anthropic"],"title":"Anthropic releases Claude Opus 4.8 with cheaper fast mode and Claude Code \"dynamic workflows\"","summary":"Claude Opus 4.8 (`claude-opus-4-8`) launched on May 28, 2026 at the same $5/$25 price as Opus 4.7. It improved agentic coding, computer use and honesty, and Anthropic said Mythos-class models would reach all customers within weeks. Fast mode (2.5x speed) became three times cheaper, and Claude Code gained 'dynamic workflows' that can fan out to hundreds of parallel subagents.","key_facts":["Released May 28, 2026; model id claude-opus-4-8; $5/$25 per 1M tokens; fast mode $10/$50","Context 1M tokens on Claude API, Bedrock and Vertex AI (200K on Microsoft Foundry); 128K output","Online-Mind2Web 84%; OSWorld-Verified 82.3% (Anthropic)","Claude Code dynamic workflows (research preview) spawn hundreds of parallel subagents; effort slider added to claude.ai and Cowork","'Ultracode' (Claude Code v2.1.154, May 28, per Pilot Shell): a toggle on the /effort slider that makes Claude orchestrate dynamic workflows for substantive tasks; Anthropic's docs call it 'a Claude Code setting rather than a model effort level'. `--effort ultracode` (or Agent SDK effortLevel 'ultracode') turns it on and sets effort to xhigh; the model effort ladder stays low/medium/high/xhigh/max. Uses many more tokens per request. Later popular in 'Opus 5.5 ultracode' demo videos","Opus 4.8 later served as fallback model for Fable 5 / Opus 5.5 cyber classifier blocks"],"key_numbers":[],"tags":["llm","claude","opus","claude-code","fast-mode"],"science":null,"body_md":"## What happened\n\nTesters found Opus 4.8 \"more reliable and sharper in its judgement\" on agentic tasks and more likely to flag uncertainty instead of making unsupported claims. The same day Anthropic announced its $65B Series H. The accompanying Claude Code video promoted `/goal` and `/remote-control` for long-running work.\n\n## Why it matters\n\nOpus 4.8 was the last Opus 4.x release and a bridge to the Mythos-class releases in June. It is still used as the fallback model inside Anthropic's safeguard stack.","disputed":[],"related":[{"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-anthropic-series-h-965b","url":"https://postcutoff.com/e/2026-05-28-anthropic-series-h-965b/","date":"2026-05-28","date_precision":"day","short_title":"Anthropic raises $65B Series H at $965B valuation, passing OpenAI","deck":null,"takeaway":"By private valuation, Anthropic became the most valuable AI lab.","category":"business","category_label":"Business","importance":4,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":3,"official":1,"filed":"2026-09-29","updated":"2026-09-29","orgs":["Anthropic"]},{"id":"2026-04-16-claude-opus-4-7","url":"https://postcutoff.com/e/2026-04-16-claude-opus-4-7/","date":"2026-04-16","date_precision":"day","short_title":"Anthropic releases Claude Opus 4.7, admits it trails the unreleased Mythos Preview","deck":null,"takeaway":"It was the first time a lab shipped a flagship while publicly saying it had a stronger model it would not release.","category":"model-release","category_label":"Model releases","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":5,"official":1,"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":[],"videos":[{"id":"claude-opus-4-8-long-running-tasks","title":"Embrace long-running tasks with Opus 4.8 and Claude Code","url":"https://postcutoff.com/v/claude-opus-4-8-long-running-tasks/"},{"id":"yt-alex-finn-claude-opus-4-8-actually-blew-my-mind","title":"Claude Opus 4.8 actually blew my mind...","url":"https://postcutoff.com/v/yt-alex-finn-claude-opus-4-8-actually-blew-my-mind/"},{"id":"yt-brock-mesarich-ai-fo-anthropic-just-dropped-claude-opus-4-8-f","title":"Anthropic Just Dropped Claude Opus 4.8 (Full Breakdown)","url":"https://postcutoff.com/v/yt-brock-mesarich-ai-fo-anthropic-just-dropped-claude-opus-4-8-f/"},{"id":"yt-ai-foundations-new-claude-sonnet-5-vs-opus-4-8-full-rev","title":"NEW Claude Sonnet 5 vs Opus 4.8! (Full Review)","url":"https://postcutoff.com/v/yt-ai-foundations-new-claude-sonnet-5-vs-opus-4-8-full-rev/"},{"id":"yt-bijan-bowen-claude-opus-4-8-is-here-is-this-the-best","title":"Claude Opus 4.8 Is HERE – Is THIS the Best Model Yet?","url":"https://postcutoff.com/v/yt-bijan-bowen-claude-opus-4-8-is-here-is-this-the-best/"},{"id":"yt-teacher-s-tech-claude-fable-5-better-than-opus-4-8","title":"Claude Fable 5: Better Than Opus 4.8?","url":"https://postcutoff.com/v/yt-teacher-s-tech-claude-fable-5-better-than-opus-4-8/"},{"id":"yt-prompt-engineering-claude-opus-4-8-here-is-everything-that","title":"Claude Opus 4.8: Here is Everything that Changed","url":"https://postcutoff.com/v/yt-prompt-engineering-claude-opus-4-8-here-is-everything-that/"},{"id":"yt-the-ai-advantage-claude-opus-4-8-full-breakdown-testing-a","title":"Claude Opus 4.8 Full Breakdown & Testing (AI News You Can Use)","url":"https://postcutoff.com/v/yt-the-ai-advantage-claude-opus-4-8-full-breakdown-testing-a/"},{"id":"yt-arena-ai-claude-opus-4-8-first-impressions","title":"Claude Opus 4.8 | First impressions","url":"https://postcutoff.com/v/yt-arena-ai-claude-opus-4-8-first-impressions/"},{"id":"yt-tonbi-s-ai-garage-first-look-at-claude-opus-4-8","title":"First Look at Claude Opus 4.8","url":"https://postcutoff.com/v/yt-tonbi-s-ai-garage-first-look-at-claude-opus-4-8/"}],"models":[],"changes":[{"date":"2026-10-11","type":"edit","text":"Added the ultracode setting"},{"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":"2026-10-11","human_review":null,"version":{"date":"2026-10-11"}},"gaps":[{"model_id":"gpt-6-astra","name":"GPT-6 Astra","cutoff":"2026-04","days_after":28,"in_training_data":false},{"model_id":"claude-opus-5-5","name":"Claude Opus 5.5","cutoff":"2026-06","days_after":null,"in_training_data":true},{"model_id":"gemini-4-hydrogen","name":"Gemini 4 Hydrogen","cutoff":"2026-03","days_after":58,"in_training_data":false},{"model_id":"grok-4-7","name":"Grok 4.7","cutoff":"2026-05","days_after":null,"in_training_data":true}],"short_url":null}