Claude Sonnet 5.5 — Faster Sonnet, Same Premium Band

September 29, 2026

Claude Sonnet 5.5 is in the model picker. Anthropic's newest Sonnet is a clear step up from Sonnet 5 on coding and knowledge work, writes output more than 30% faster, and finishes tasks with fewer tool calls — on the same Premium 6× band as Sonnet 5. 1M context, adaptive thinking, 128K output. Sonnet 5 stays in the picker.

What you can do

• Pick Claude Sonnet 5.5 - Reasoning from the model selector on any paid plan. Search "Sonnet" or find it next to Sonnet 5.
• Start from the new-chat card. It says Try out the latest Claude Sonnet 5.5, GPT-6 Sol and Opus 5.5 and opens the picker on the Sonnet 5.5 row.
• Run long agent loops faster. Same 1M context and 128K output as Sonnet 5, with quicker output and fewer round-trips per task.
• It is eligible for Auto. Workhorse tier, quality 62. Auto still picks the cheapest healthy model that clears the task's quality floor, so pin Sonnet 5.5 when that turn should run on it. EU Data Residency keeps it available on the EU Bedrock profile.
• Use it in a Swarm. Worker steps can be assigned Sonnet 5.5, including when EU Data Residency is on.
• Pay the same band. Sonnet 5.5 sits on Premium 6×, the band Sonnet 5 and Sonnet 4.6 use.

Where this shows up

You've been pinning Sonnet 5 for big refactors and tool-heavy research loops. Switch the pin to Sonnet 5.5 and the same jobs come back sooner, on the same band.

You leave the model on Auto for everyday work. Auto can land on Sonnet 5.5 only when it is the cheapest healthy model that clears the quality floor. Pin it when you want this model on the job.

You run with EU Data Residency on. Nothing changes for you yet: Sonnet 5 stays your Anthropic workhorse (see Heads up).

Try it

• "Using Claude Sonnet 5.5, refactor this module for async I/O, keep the public API stable, and list every change that could break a caller."
• "Read this whole repo and find the three architectural decisions that will hurt us at 10× scale."
• "Plan a three-step research swarm: market scan, competitor pricing, then a one-page recommendation."

Heads up

• Premium band — 6× tokens. Same band as Sonnet 5 and Sonnet 4.6; billed at the Premium multiplier on your plan quota.
• EU profile added October 16. At launch Sonnet 5.5 was global-only and hidden under EU Data Residency. AWS now publishes eu.anthropic.claude-sonnet-5-5. EU accounts use that profile, and the picker shows the EU flag. See October 16.
• No harness numbers yet. Can it Run Alfrada? still shows Sonnet 5 until 5.5 has a full run.