Route each request to a cheap 7B or expensive 70B model to maximize satisfaction minus cost. Design the online router.
A static threshold on prompt length leaves money on the table both ways. The router that learns is a contextual bandit, and the interview lives in the reward function and the cold-start handling, not the algorithm name.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
A static threshold on prompt length leaves money on the table both ways. The router that learns is a contextual bandit, and the interview lives in the reward function and the cold-start handling, not the algorithm name.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
