Decision boundary
Do not start with which model is absolutely stronger. Start with the boundary: cost, context, speed, quality, ecosystem, or supply stability.
- GPT-5.5 Pro is worth checking first when the GPT-5.5 family, 1M context, and text+image+file->text capability match the job.
- Claude Sonnet 4.6 is worth checking first when the Claude family, 1M context, and text+image->text capability match the job.