Migrating a Production AI Agent to GPT-5.6: 2.2x Faster and 27% Cheaper

Migrating a production AI agent to GPT-5.6: 2.2x faster, 27% cheaper

We switched our production agent from Claude Opus to GPT-5.6 Sol, achieving 2.2x faster builds at 27% lower cost. This migration required fixing our evaluation harness and adapting to GPT-5.6's unique behaviors, such as its tendency to fill all tool parameters and its distinct prompt caching mechanics. By redesigning our tool schemas and cache strategy, we unlocked significant performance gains while maintaining high-quality output.

"Your harness is tuned to your incumbent model, and you don't know it."