Perplexity is the classic LM metric. The signal is knowing it is just exponentiated cross-entropy, what it intuitively measures, and why a low perplexity does not mean a good product.
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What is perplexity, and what are its limits as a language-model metric?
Perplexity is the classic LM metric. The signal is knowing it is just exponentiated cross-entropy, what it intuitively measures, and why a low perplexity does not mean a good product.
Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.
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