Simon Willison's GPT-5.6 verdict: "Sol on Medium" is his new coding default, and the model picker is a mess.

In his July 9 annotated write-up he flags Sol at Medium reasoning as a likely upgrade over 5.5 xhigh for coding, and calls the programmatic-tool-calling and multi-agent API additions the genuinely interesting parts (simonwillison.net). Sol also sets a new high of 53.6 on Agents' Last Exam, beating Claude Fable 5 by 13.1 points at roughly a quarter of the estimated cost. His real complaint: figuring out which variant times which reasoning-effort to use is now the hardest part of adopting the family. He's not wrong. Three tiers times four effort levels is twelve combos to reason about per task.