GPT-5.6 Prompt Optimization: The Lean Way to 66% Token Cuts

Stop Over-Prompting GPT-5.6: Why Leaner Instructions Deliver Better Results Working with GPT-5.6 is like onboarding a brilliant but impatient new hire. The more you try to micromanage every step, the more likely it is to go off the rails. Instead of spending hours writing lengthy system prompts, focus your energy on clarifying the outcome and defining the stopping conditions. Earlier this year, OpenAI rolled out GPT-5.6. Our team immediately migrated our internal coding-agent pipeline to test it out. The results were counterintuitive: our old, verbose prompts—the ones that worked perfectly fine on GPT-5.5—actually hurt performance. When we stripped down the …