What is causal masking, and why does it let you train on every position in a sequence at once?
One triangle of negative infinity, added before the softmax, is what makes transformer training parallel and generation stubbornly serial. Interviewers want the mechanism and the asymmetry it creates, not a definition of attention read back to them.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
One triangle of negative infinity, added before the softmax, is what makes transformer training parallel and generation stubbornly serial. Interviewers want the mechanism and the asymmetry it creates, not a definition of attention read back to them.
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.
