Migrating: GPT-5.4 to GPT-5.6 Sol

Moving from last generation's frontier model to the current one, and unlike a lot of migrations on this site, the window and rate-limit group don't change at all — this is a narrower migration than it might sound.

What actually moves

Knowledge cutoff jumps forward by several months — the concrete, immediate benefit of this specific migration. Price moves upward on both input and output at every tier; Sol is the more expensive of the two. And Sol introduces a charge for writing into the prompt cache, a cost GPT-5.4 simply doesn't have — a caching-heavy workload moving over needs to re-run its cache economics, not just its per-token budget.

What stays put

Context window, maximum output length, rate-limit group, and the long-context repricing rule all carry over unchanged. A workload sized against GPT-5.4's window and throughput ceiling doesn't need to be re-sized for this specific move.

What to check before switching

Run any caching-heavy workflow through the prompt-caching savings calculator against Sol specifically before assuming the migration is cost-neutral beyond the sticker price — the write charge is new, and it can change the caching math meaningfully even when nothing else about the workload changes. If recency is the only thing driving this migration and price sensitivity is real, Terra is worth checking too: same window, same rate-limit group, and a lower price than Sol at every tier.