Claude System Prompt Compliance Degrades in Long Conversations

A Reddit user reports that Claude's system prompt compliance degrades significantly in long conversations, particularly affecting AI coding agents with specific formatting rules and constraints.

Problem Details

The user runs multiple Claude-based agents for internal tooling, each with system prompts containing specific rules about output format, topics to avoid, and edge case handling. While these work perfectly for the first 20-30 exchanges, compliance begins slipping around message 40-50.

Specific issues observed:

• Agents stop following formatting rules
• They become "helpful" in ways the system prompt explicitly prohibits
• They forget constraints that were clear at the start

The user notes this isn't a bug but rather how context windows work under pressure, with system prompts competing with 40+ messages of conversation history for attention weight.

Workarounds and Solutions

The user shares several practical approaches that have worked:

• Restate critical rules: Every 15-20 messages, restate the top 3 rules you can't afford to lose in condensed form (not the full system prompt)
• Keep conversations shorter: If a task requires more than 30 exchanges, start a new session with a summary of what happened
• Strategic prompt placement: Put your most important constraints at both the beginning AND end of the system prompt, as models pay more attention to both positions
• Test at scale: Test your agents at message 50, not just message 5, since happy path demos don't reveal this issue

The user emphasizes that this problem isn't discussed enough and invites others to share reliable patterns for maintaining instruction adherence in long-running sessions.