{"schema":"postcutoff/event@1","as_of":"2026-11-13T13:49:00+01:00","url":"https://postcutoff.com/e/2026-02-17-claude-sonnet-4-6/","md":"https://postcutoff.com/e/2026-02-17-claude-sonnet-4-6/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":"2026-02-17-claude-sonnet-4-6","date":"2026-02-17","date_precision":"day","short_title":"Anthropic releases Claude Sonnet 4.6","deck":null,"takeaway":"Claude Sonnet 4.6 (claude-sonnet-4-6) was released on February 17, 2026 with a 1M-token context and 128K output.","category":"model-release","category_label":"Model releases","importance":2,"confidence":"medium","status":{"key":"partly","labels":["Partly confirmed"]},"sources":[{"n":1,"title":"Anthropic Claude model release timeline (hidekazu-konishi.com)","url":"https://hidekazu-konishi.com/entry/anthropic_claude_model_release_timeline.html","type":"discussion","group":"reactions","domain":"hidekazu-konishi.com"},{"n":2,"title":"Everything Anthropic shipped in 2026 (Linas Substack)","url":"https://linas.substack.com/p/anthropic-claude-2026-every-launch-guide","type":"discussion","group":"reactions","domain":"linas.substack.com"}],"official":0,"filed":"2026-09-29","updated":"2026-09-29","orgs":["Anthropic"],"title":"Anthropic releases Claude Sonnet 4.6","summary":"Claude Sonnet 4.6 (`claude-sonnet-4-6`) was released on February 17, 2026 with a 1M-token context and 128K output. It stayed the default Free/Pro model until Sonnet 5 replaced it on July 1, 2026.","key_facts":["Released February 17, 2026; model id claude-sonnet-4-6; 1M context, 128K output (third-party timeline)","Replaced as Free/Pro default by Sonnet 5 on July 1, 2026"],"key_numbers":[],"tags":["llm","claude","sonnet"],"science":null,"body_md":"## What happened\n\nA mid-tier update following Opus 4.6. The details here come from third-party timelines; the official announcement was not fetched.\n\n## Why it matters\n\nIt was the workhorse default model for most Claude users in the first half of 2026.","disputed":[],"related":[{"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"]},{"id":"2026-02-05-claude-opus-4-6","url":"https://postcutoff.com/e/2026-02-05-claude-opus-4-6/","date":"2026-02-05","date_precision":"day","short_title":"Anthropic releases Claude Opus 4.6 with 1M context, adaptive thinking and agent teams","deck":null,"takeaway":"It made 1M-token context and adaptive thinking standard features of Anthropic's flagship line.","category":"model-release","category_label":"Model releases","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":4,"official":1,"filed":"2026-09-29","updated":"2026-09-29","orgs":["Anthropic"]}],"people":[],"posts":[],"videos":[],"models":[],"changes":[{"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":"2026-09-29","human_review":null,"version":{"date":"2026-10-04"}},"gaps":[{"model_id":"gpt-6-astra","name":"GPT-6 Astra","cutoff":"2026-04","days_after":null,"in_training_data":true},{"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":null,"in_training_data":true},{"model_id":"grok-4-7","name":"Grok 4.7","cutoff":"2026-05","days_after":null,"in_training_data":true}],"short_url":null}