The senior LLM-engineering interview in 2026 is a 7-pillar coverage exercise. Whatever the scenario, your answer covers model selection, context strategy, evaluation, latency, cost, reliability, and monitoring — and your reasoning matters more than the choices themselves. Pick a scenario below; make a choice on each pillar; see how each option scores against an interviewer rubric and what the reasoning should sound like. The same option scores differently across scenarios — what makes a strong answer for medical Q&A is overkill for chat support and inadequate for a code agent.