Anthropic’s Claude Code regression postmortem is unusually specific. In an April 23 engineering note, the company said three vendor-side changes made Claude Code feel worse for users, while the API and inference layer were not impacted . That distinction matters. This was not Anthropic saying the underlying model weights were broadly downgraded. It was saying that defaults, cache behavior, and system-prompt instructions inside a hosted product changed the model’s effective intelligence anyway. What Anthropic admitted changed in Claude Code regression Anthropic’s postmortem names three issues, with dates, affected products, and reversions. All three were resolved by April 20 in Claude Code v2.1.116.…