Not sure everyone will agree with you to have a simple default preference that might cost double the fast requests. For simple tasks why not choose the agent-less yet 0 fast requests deekseek-v3 for Edit and Ask Modes, and the 1/3 fast requests o3-mini for Agent Mode? Then for more complex tasks, choose by claude-3.7-sonnet and as a last resort, claude-3.7-sonnet-thinking?
P.S.
Please consider renaming the title word heuristics and perhaps the entire phrase into a more SEO friendly one (e.g. “Please clarify how does Cursor auto-select a model”) so that more people will notice this thread.