Anthropic retires Claude Sonnet 4 and Opus 4 on June 15, five days from now

Anthropic announced on June 5, 2026 that Claude Sonnet 4 (claude-sonnet-4-20250514) and Claude Opus 4 (claude-opus-4-20250514) will be retired from the Claude API on June 15, 2026—five days from today. Any application calling these model IDs directly will begin receiving API errors at the retirement deadline.

What's new

The two models being retired and their Anthropic-recommended replacements:

• claude-sonnet-4-20250514 → migrate to claude-sonnet-4-6 (latest Sonnet snapshot)
• claude-opus-4-20250514 → migrate to claude-opus-4-8 (latest Opus flagship)

The same June 5 update also deprecated fast mode for Claude Opus 4.6, with removal scheduled approximately 30 days after the fast mode launch. Developers using Opus 4.6 in fast mode should switch to fast mode on Opus 4.7 or Opus 4.8.

Separately, Claude Opus 4.1 (claude-opus-4-1-20250805) was deprecated at the same time with a longer runway—its retirement on the Claude API is scheduled for August 5, 2026.

Context

Claude Sonnet 4 and Claude Opus 4 both shipped in May 2025. They were the first models in Anthropic's 4.x series, with Sonnet 4 positioned for everyday tasks and Opus 4 as the top-tier reasoning model at launch. Both have since been superseded by multiple successor versions as Anthropic's release cadence accelerated through late 2025 and into 2026.

The successor models use the updated tokenizer introduced with Claude Opus 4.7. That tokenizer produces roughly 30% more tokens for the same input text compared to models before 4.7, a relevant cost and context-window consideration for teams migrating in production.

Anthropic has maintained a six-month deprecation window for most models, but the Sonnet 4 / Opus 4 retirement timeline was shorter given the pace of model releases. Developers who pinned claude-sonnet-4-20250514 or claude-opus-4-20250514 in their API calls—rather than using versioned aliases like claude-sonnet-4-6-latest—are the ones at immediate risk.

Why it matters

The June 15 deadline is now urgent. Teams should audit any production code that references these model IDs directly. Anthropic's migration guide covers the API-level changes between generations, including the tokenizer shift, the deprecation of manual extended thinking in favor of adaptive thinking on newer models, and the removal of assistant prefill support on Fable 5 and Mythos 5.

For teams that have been holding on to earlier model snapshots for reproducibility or budget reasons, the June 15 cutover forces a migration decision this week. The broader pattern—Sonnet 4 and Opus 4 retiring while Opus 4.1 gets until August—reflects Anthropic's strategy of giving longer deprecation windows to models with larger install bases, while moving faster on first-generation 4.x variants that launched alongside a more capable sibling within months.