What happened
What happened: Anthropic’s Sep 28, 2026 Sonnet 5.5 launch keeps list rates unchanged vs Sonnet 5 ($2 input / $10 output per MTok; cache read was $0.20 at launch; as of 2026-10-09 docs cache hits are $0.10 (0.05× input)) while claiming up to ~30% less $ per task and 30%+ faster via fewer tokens/steps. Opus 5.5 sits at $4/$20 as the judgment tier. Migration note: Sonnet 5 apps may hit breaking changes (between_tools, thinking/tool shape). Tool impact: sticker parity is not bill parity — Cursor / Claude Code / API agent loops should re-measure $/merged-PR for a week; Max effort or messy tool-loops can erase the savings.
Tool impact
Switch or not?
As of 9 Oct 2026: switch API/default agent traffic to Sonnet 5.5 this week if jobs are well-scoped coding/docs; keep Opus 5.5 for open-ended judgment. Don’t treat same $2/$10 as same monthly burn — re-measure $/merged-PR for 7 days, and recompute cache-heavy loops at $0.10/MTok cache reads. At Max effort some third-party notes say cost can rise — verify on your traces. Pair with the new Haiku 5.5 + Max API credits card for short-prompt overflow.
Money / risk
Sticker parity ≠ bill parity; Max effort / tool-loop shape can erase savings; migration breaks can waste eng time before any token win shows up. Cache-read cut to $0.10 only helps if your traces actually hit cache.
Sources (multi-channel)
GitHub, docs, blogs, video — not a single-platform dump.
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blog
Anthropic — Claude Sonnet 5.5 announcement
Vendor claims on effective cost/speed; list price parity vs Sonnet 5.
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docs
Anthropic — Pricing
Verify Sonnet 5.5 $2/$10, Opus 5.5 $4/$20, and cache hits $0.10 (0.05×) on platform docs as of 2026-10-09.
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docs
Anthropic docs — Models overview
Migration / tool+thinking shape notes for Sonnet 5 → 5.5 apps.
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docs
Anthropic — Claude API pricing (Sonnet 5.5 cache 0.05×)
Official cache hits $0.10/MTok for Sonnet 5.5 as of 2026-10-09.
Source
Anthropic — Claude Sonnet 5.5 · verify independently