Migrating: GPT-5.5 to GPT-5.6 Sol

The smallest step on this site's migration list in terms of what actually changes — these two share a context window, a rate-limit group, and the long-context repricing rule, which makes this migration almost entirely about two things: recency, and how caching gets billed.

What actually moves

Sol's knowledge cutoff runs meaningfully more recent than GPT-5.5's — the clearest, most immediate reason to make this move. Standard input and output pricing is identical between the two, so unlike most migrations on this list, price isn't a factor in the decision at all. The one real cost-side change is caching: GPT-5.5 writes to the cache for free, while Sol charges the GPT-5.6-family markup on every write.

What stays put

Window, maximum output, rate-limit group and the long-context rule are all unchanged. A workload sized against GPT-5.5 doesn't need re-sizing for this move on any of those axes.

What to check before switching

If your task doesn't depend on very recent knowledge, this migration is close to a wash except for caching — and for a workload that writes many cache prefixes without reading most of them back, GPT-5.5's free writes can make it the cheaper real-world choice despite matching Sol on every other published number. Run the actual caching pattern through the prompt-caching savings calculator before assuming "newer" is automatically "better" here; this is the one pairing on this site where it genuinely might not be, cost-wise.