reactordev pretty much got it right. In the config, you say "this role uses this model". You decide up front which model handles which kind of task, instead of one model doing everything. All config driven.

You're not choosing a model every time you prompt. It's already set in your config. The main shift in the mind is writing prompts to a role rather than to a specific model.

define roles for your agents, add roles to config that have specific models, use those models for those roles. Not the author but this is how I did mine.