Anthropic retires Claude Sonnet 4 and Claude Opus 4, all requests to legacy model IDs now return errors

Anthropic retired two original Claude 4 models — Claude Sonnet 4 and Claude Opus 4 — effective June 15, 2026. All API requests to the model IDs claude-sonnet-4-20250514 and claude-opus-4-20250514 now return errors, ending support for the models that launched the Claude 4 generation just over a year ago.

What's new

Both models reached end-of-life today:

• Claude Sonnet 4 (claude-sonnet-4-20250514) — retired. Recommended replacement: Claude Sonnet 4.6
• Claude Opus 4 (claude-opus-4-20250514) — retired. Recommended replacement: Claude Opus 4.8

Anthropic's platform release notes confirm: "We've retired the Claude Sonnet 4 model (claude-sonnet-4-20250514) and the Claude Opus 4 model (claude-opus-4-20250514). All requests to these models will now return an error. We recommend upgrading to Claude Sonnet 4.6 and Claude Opus 4.8 respectively."

Developers who have not migrated away from these model IDs are seeing immediate failures today. There is no grace period once a retirement takes effect. Anthropic has made an External Researcher Access Program available for academic users who need continued access for reproducibility purposes.

A third model, Claude Opus 4.1 (claude-opus-4-1-20250805), was separately flagged for retirement on August 5, 2026, giving those integrations roughly seven more weeks to migrate.

Context

The original Claude 4 models launched on May 14, 2025 — 13 months ago. They were the first generation of the Claude 4 family, establishing the foundation for the extended-thinking and reasoning capabilities that defined subsequent releases.

The pace of Anthropic's model succession has accelerated significantly. Claude Opus 4.8 arrived on May 28, 2026, with a 1M token context window and adaptive thinking that only triggers when a turn requires it. Claude Fable 5, Anthropic's most capable widely released model, launched on June 9 — six days ago — supporting 1M context by default, 128k max output tokens, and always-on adaptive thinking. With two major model releases in under two months, the original Claude 4 models became redundant quickly.

Applications migrating from the original Claude 4 models to Opus 4.8 or Fable 5 should note that the tokenizer changed with Claude Opus 4.7 — the same text now produces roughly 30% more tokens on current models compared to the original Claude 4 generation.

Why it matters

For any developer still pinning to the retired model IDs, today is an emergency. The retirement is immediate with no warning window. Any hardcoded claude-sonnet-4-20250514 or claude-opus-4-20250514 reference in production is now broken.

The practical migration path is clear: Sonnet 4 workloads move to Claude Sonnet 4.6; Opus 4 workloads move to Claude Opus 4.8. Neither requires switching to the new tokenizer generation unless upgrading beyond those targets.

More broadly, the speed of this retirement cycle signals a new operating rhythm for teams building on Anthropic's API. Model IDs from 2025 are now retiring in 2026, and Claude Opus 4.1 — itself a relatively recent model — retires in August. Teams that pin to specific model IDs rather than version aliases should plan for quarterly lifecycle reviews.