•Anthropic's Claude Code (Opus) has reportedly suffered a significant quality regression for complex engineering tasks since February 2026 updates.
•Analysis of nearly 18,000 thinking blocks points to 'thinking content redaction' and a drastic reduction in model 'thinking depth' as the primary culprits.
•The model now frequently ignores instructions, offers incorrect fixes, and exhibits 'edit-first' behavior, making it unreliable for senior engineering workflows.
•The regression's timeline precisely correlates with the rollout of thinking content redaction, indicating a structural requirement for extended thinking.
•Anthropic's Claude Code (Opus) has reportedly suffered a significant quality regression for complex engineering tasks since February 2026 updates.
•Analysis of nearly 18,000 thinking blocks points to 'thinking content redaction' and a drastic reduction in model 'thinking depth' as the primary culprits.
•The model now frequently ignores instructions, offers incorrect fixes, and exhibits 'edit-first' behavior, making it unreliable for senior engineering workflows.
•The regression's timeline precisely correlates with the rollout of thinking content redaction, indicating a structural requirement for extended thinking.
