Claude Sonnet 4 and Opus 4 to Be Retired on June 15

Anthropic has confirmed that Claude Sonnet 4 and Opus 4 will be retired on June 15, closing out the generation that carried the lab through most of 2025 — here is what teams need to do before the deadline.

Claude Sonnet 4 and Opus 4 to Be Retired on June 15

Anthropic has confirmed the retirement date for Claude Sonnet 4 and Opus 4: June 15, 2026. After that date, API requests pinned to the 4-series flagships will fail, and teams still running them will be migrated onto the 5-series by force rather than by choice.

The retirement closes the book on the generation that defined Anthropic's 2025 — the models that made Claude a default answer in coding assistants and enterprise agent deployments. But model generations in 2026 have short lives, and the 5-series is already rolling out with Sonnet 5 in general availability.

What teams should do before June 15: inventory every integration that references sonnet-4 or opus-4 model identifiers, including aliases that silently resolve to them; re-run evaluation suites against Sonnet 5 and Opus 4.7 to confirm output quality on real traffic; and update any prompt logic tuned to 4-series behavioral quirks, which do not all carry forward unchanged.

What not to worry about: context handling, tool-use APIs, and response formats remain compatible across the transition, so infrastructure changes should be minimal. This is a revalidation exercise, not a rewrite.

The larger lesson is schedule discipline. With Anthropic shipping successive generations quickly and rivals on similar cadences, retirement notices are becoming routine industry events. Treat model APIs as perishable dependencies with explicit expiry management — the teams that did this before the 4-series sunset are spending this week on roadmap, not on migration.