Sonnet 4.6 is the price-performance default. At $3/$15 per million tokens with a 1M-token window and strong coding, it is the model most teams put behind the bulk of their agent steps, escalating to Opus 4.8 only for work that is expensive to get wrong. The economics are the argument: you can run far more of your workflow on Sonnet before the token bill forces a decision.
GPT-5.6 Sol is the newest flagship and it shows on multi-step coding and agentic runs, where it is genuinely strong. The cost is the catch. At $5/$30 output it is double Sonnet on the pricey side, so Sol earns its place on high-stakes steps rather than high-volume ones. The upside of the July 2026 launch is the three-tier family: Sol, Terra, and Luna let you route by cost inside one provider.
The real answer is not one model, it is routing. Put Sonnet 4.6 (or GPT-5.6 Terra) on the high-volume, lower-stakes steps, and reserve Opus 4.8 or GPT-5.6 Sol for the decisions where a wrong answer is expensive. If you have to pick a single default in 2026, Sonnet 4.6 wins on economics for most workloads. Reach for Sol when the step is hard enough that the price stops mattering.