Migrating: GPT-5.5 to GPT-5.6 Sol

This used to be the smallest step on the migration list: the same window, the same rate-limit table, the same long-context rule and, at the time, the same price — leaving recency and caching as the only things that moved. Two changes since then make it a different decision.

Price now moves down

Sol's August promotional cut put it below GPT-5.5 on input, cached input and output, at every tier both publish. Caching no longer favors GPT-5.5 either: its written tokens bill at its ordinary input rate, and Sol's cache-write rate is now that same figure, with cheaper reads after it. The page's old advice — that GPT-5.5's "free writes" could make it the cheaper real-world choice — rested on reading those writes as free, and no longer holds on any workload.

The deadline

GPT-5.5 retired from ChatGPT, ChatGPT Work and Codex on October 14, 2026. For Codex with ChatGPT sign-in, OpenAI's named replacement on paid plans is GPT-6.1 Sol rather than GPT-5.6 Sol, and GPT-6.1 Sol is cheaper than both on input and output. API users keep GPT-5.5.

What actually changes in behavior

Sol adds the max effort level above xhigh; both default to medium. Sol's knowledge cutoff is newer as well.

Before switching

Note that Sol's prices are promotional, available at least through November 21, 2026. If you're moving off GPT-5.5 because of the retirement, test GPT-6.1 Sol first — it is the replacement OpenAI names, and its price carries no promotional label.