Definition. selected-token surprisal [shannon1948mathematical, Part I, Section 6] [ftip-0064]
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    For a sampled token \(\xi _t\) under next-token law \(\pi (\,\cdot \mid \mathsf H_t)\), its surprisal is

    \[-\log \pi (\xi _t\mid \mathsf H_t).\]

    It is a random value attached to the selected token. Its conditional expectation over the token equals the finite Shannon entropy of the next-token law.