Breaking

Anthropic Launches Claude Sonnet 5.5 With Faster Output and Lower Per-Task Costs

September 29, 2026 at 12:51 EDT

Foundation Models
AI Agents
Software Dev & Coding

Anthropic released Claude Sonnet 5.5 on September 28, 2026, positioning it as a faster and more economical upgrade to Claude Sonnet 5 for coding, agents and everyday knowledge work. The company says Claude Sonnet 5.5 generates output 30%+ faster than Sonnet 5 and can cost up to 30% less per task, even though its listed API price remains $2 per million input tokens and $10 per million output tokens.

Sep 28, 2026 · Anthropic

Claude Sonnet 5.5 speeds up the workhorse

The new Sonnet model keeps Sonnet 5 token pricing while Anthropic claims faster output, lower per-task costs and much stronger coding-agent results.

30%+

faster output than Sonnet 5

-30%

up to lower cost per task

$2/$10

input and output per 1M tokens

token context window

Parallel-agent search widened in the same 10 seconds

A four-agent run explored more than twice as many positions on Sonnet 5.5.

120

Sonnet 5 positions

251

Sonnet 5.5 positions

Takeaway: the same wall-clock budget can support broader agent search, not just faster single answers.

Where it looks strong

Well-scoped coding, bug fixes, document work, UI polish and repeatable agent runs where speed and cost matter.

Where caution remains

Open-ended architecture and hard debugging still favor Opus 5.5, and high effort can consume many tokens.

Migration watchlist

Use `between_tools` to turn off up-front thinking.
Forced tool use is not supported.
Thinking blocks are bound to the model and conversation.
Update older computer-use integrations on the Claude API and Google Cloud.

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