Every chat model decodes with top-p, but few candidates can build it from logits: softmax, sort, take the smallest set of tokens whose cumulative probability crosses p, renormalize, sample. The screen for whether you understand decoding, not just call an API.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
Every chat model decodes with top-p, but few candidates can build it from logits: softmax, sort, take the smallest set of tokens whose cumulative probability crosses p, renormalize, sample. The screen for whether you understand decoding, not just call an API.
The two real tests are numerical-stable softmax (subtract the max before exp, or large logits overflow) and the off-by-one on the cumulative cutoff: you must always keep the first token that crosses p, never an empty set. A candidate who truncates before including the crossing token can produce an empty nucleus and crash. The follow-up on top-p versus temperature versus top-k separates people who tuned these in production from people who read a blog post.
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