GPT-5.6 Migration: What Changed, and What a Real Agent Move Actually Saved

A GPT-5.6 migration is now a real decision for agent teams: OpenAI's new Luna/Terra/Sol tiers landed July 9, and one production team already reported a migrated agent running 2.2x faster and 27% cheaper. Here's what changed and how to think about the switch.

07/13/2026 · Model Evaluation · 8 min read