Design a large-scale text classification system (e.g. news categorization or topic tagging).

Tagging articles at scale is bread-and-butter ML, but the easy version fails three ways: it is multi-label, the taxonomy is hierarchical and keeps growing, and rare classes hide behind aggregate accuracy. The signal is the model choice plus how you handle all three.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.