Claude Sonnet 4 reaches end of life in Kiro

What changed

Claude Sonnet 4 is no longer available in Kiro as of October 14, 2026. Kiro tells users to pick another model before continuing work that used it, points to Claude Sonnet 5.5 as the current Sonnet, and lists upcoming retirements on its model lifecycle page.

Who it affects

Kiro users and workflows pinned to Claude Sonnet 4.

What to do

Move agents, hooks and workflows that name Sonnet 4 to Sonnet 5.5 or another model.

Source: https://kiro.dev/changelog/models/claude-sonnet-4-end-of-life/