Instruction Position in System Prompt Determines Compliance Rate

Instructions placed in the first 200 tokens of a system prompt have significantly higher compliance rates than identical instructions placed in the middle or end of long system prompts.

Tested 12 formatting and behavioral constraints across system prompts of 500, 1500, and 3000 tokens. Compliance with constraints in first 200 tokens: 94%. Middle of prompt: 71%. Last 200 tokens: 68%. Models attend to context non-uniformly even within system prompt — early instructions are weighted more heavily.

Structure system prompts with critical constraints first. Use a "Critical rules" block at the very top before persona description, context, or background. This is especially important for safety constraints, output format requirements, and domain restrictions.