Anthropic releases Claude Sonnet 5.5 and its system card

1. #0109.28
   Initial2026-09-28 18:01 · publication time

   Introducing Claude Sonnet 5.5 - Anthropic

   Anthropic announced the release of Claude Sonnet 5.5, the latest iteration of its mid-tier frontier model family.

   Source evidence: Anthropic News · Anthropic News · TechCrunch AI

2. #0209.29
   Escalation2026-09-29 06:55 · publication time

   Sonnet 5.5成首个防「推理抽取」的Sonnet：内部思考开始绑定账号

   Anthropic added anti-reasoning extraction safeguards to Sonnet 5.5: generated thinking blocks are bound to the originating account or organization, and a classifier detects large-scale harvesting of reasoning for distillation.

   State after update: Sonnet 5.5 has been released and is the first Sonnet model with anti-reasoning extraction account binding and a classifier.

   Source evidence: theblockbeats

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