GPT-6 Sol costs $2 per million input tokens and $10 per million output tokens, exactly half of Claude Opus 5.5's $4 and $20.
Cost per correct task equals cost per attempt divided by pass rate, so at list prices Opus 5.5 needs about twice Sol's pass rate to win on cost.
Opus 5.5 leads on coding and knowledge work, while Sol is cheaper on budget-tier and business-workflow tasks.