GPT-5.6 vs GPT-5.5: The Skeptic's Upgrade Migration Guide
GPT-5.6 reached general availability on July 9, 2026 at the exact $5/$30 price GPT-5.5 charged, with a February 16, 2026 knowledge cutoff and cheaper Terra and Luna tiers underneath. The quiet improvement is what disappeared: GPT-5.5's long-context surcharge above roughly 272K input tokens. But the alias default, prompt regressions, and account-specific rate limits make a careless swap riskier than it looks. For PMs, this is a worthwhile migration that should still run behind an eval suite, not as a model-string find-and-replace.
