Claude Code Deletes 80% of System Prompts in Opus 4.8, Then Adds Back 72% for Opus 5

According to Beating monitoring, Claude Code's system prompts were significantly reduced in Opus 4.8, dropping from 15,225 characters in Opus 4.7 to 4,467 characters, yet Opus 5 restored the size to 7,694 characters—a 72% increase from version 4.8. Qoder engineer Chen Cheng extracted the actual requests sent by Claude Code and discovered the major reduction occurred at version 4.8, not Opus 5. The team deleted approximately 81% of behavioral rules, replacing detailed guidelines like "avoid writing unnecessary comments" with a single instruction to "follow existing code style."

However, after Opus 5 launched, Claude Code added two new model-specific rules primarily constraining repetitive error explanations and frequent progress reports. This pattern suggests the team removes generic rules but continues adding specialized constraints when new model versions introduce new issues.