benchrWho this hits
Sonnet 4 shipped May 2025 and spent close to a year as the default recommendation for production API work — cheap enough to run at volume, strong enough to trust with real tasks. That's exactly why this retirement matters more than most. If your team built anything on Claude between mid-2025 and early 2026, odds are decent the model string says claude-sonnet-4-20250514 or the claude-sonnet-4-0 alias.
Anthropic announced the deprecation on April 14, 2026 and emails affected accounts, but notification emails go to whoever owns the API key. The engineer who pinned that model ID may have left the company. Grep for it.
The swap, in numbers
| Spec | Sonnet 4 (retiring) | Sonnet 4.6 (replacement) |
|---|---|---|
| Input / 1M tokens | $3.00 | $3.00 |
| Output / 1M tokens | $15.00 | $15.00 |
| SWE-bench Verified | 72.7% | 79.6% |
| Context window | 200K | 1,000,000 |
| Max output | 64K | 64K |
This is the rare migration with no trade-off row. Same bill, better scores, five times the context. The only real work is verification, not negotiation.
Migration checklist
1. Find every reference. Search code, config files, environment variables, and infrastructure-as-code for claude-sonnet-4-20250514 and claude-sonnet-4-0. Don't forget prompt-management tools and eval harnesses.
2. Confirm what's still calling it. Anthropic's console exports usage as CSV, broken down by API key and model. If a deprecated ID shows traffic, trace the key.
3. Swap and re-run your evals. Sonnet 4.6 follows instructions more tightly than Sonnet 4. Prompts that compensated for the older model's quirks (forced formatting, repeated constraints) sometimes over-correct on the newer one. Run your test suite before and after.
4. Watch token counts for a week. Newer Claude models tokenize differently, and long-context behavior changes how you batch documents. Costs stay flat per token, but token counts per request can shift. The calculator helps you re-budget if volumes move.
5. Check partner platforms separately. The June 15 date covers the Claude API, AWS, and Microsoft Foundry. Amazon Bedrock and Vertex AI publish their own retirement schedules. Don't assume the same date.