GPT-5.5 is in the API. Don't just bump the version string.

GPT-5.5 dropped in the OpenAI API this week — more token-efficient, better at agentic workflows, already live on Vercel's AI Gateway. But the first line of OpenAI's own migration guide is a warning: "Treat it as a new model family to tune for, not a drop-in replacement." That's the part worth paying attention to. What actually changed Two variants: gpt-5.5 for agentic coding and multi-step tool workflows; gpt-5.5-pro for demanding multi-pass work where quality beats latency. More efficient reaso