Why does the learning rate matter so much, and how do warmup and decay schedules help?

The learning rate is the single hyperparameter that can NaN your run at step 50 or stall it indefinitely. Modern training schedules it rather than pinning it to one value. Interviewers want you to know precisely what warmup and decay each give you. Here is the answer.

Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.