Claude API Old Model Strings Expire Today — No Grace Period

Today is the hard cutoff for Anthropic's deprecated Claude API model strings. Both claude-sonnet-4-20250514 and claude-opus-4-20250514 return errors from midnight June 15, 2026, with no grace period, no rollback, and no announced extension. Developers running production systems need to migrate immediately to claude-sonnet-4-6 and claude-opus-4-8 respectively. The most dangerous failure mode is silent: cron jobs, GitHub Actions, or overnight agent pipelines that reference the deprecated model strings in environment variables or configuration files. These can fail without anyone noticing until logs are checked on Monday morning. Anthropic recommends running a grep across all codebases to identify remaining references. Simultaneously, Anthropic is changing how the Claude Agent SDK, headless Claude Code, Claude Code GitHub Actions, and third-party agents are billed. Starting June 15, these automated agent workloads move off subscription limits onto a separate monthly credit system billed at API rates. Interactive Claude.ai chat and terminal Claude Code sessions remain unaffected. The credit allocation is approximately $20 for Pro, $100 for Max 5x, and $200 for Max 20x. Once exhausted, further automated usage bills at standard API pricing with no rollover. This dual change — forced model migration plus new billing — means engineering teams should audit their CI/CD pipelines and agent automation today. The migration is straightforward but unforgiving: any missed reference will break.