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Efficient turn-taking requires interlocutors to predict turn endings within a few hundred milliseconds. Beyond syntactic and pragmatic completion, prosody (especially pre-boundary lengthening) supports projection. We test whether turn-final words are longer than mid-sentence words, whether this reflects prosodic modification rather than lexical choice, and where within the word it concentrates. We analyze four corpora spanning styles and two languages (English, Spanish): Switchboard, Columbia Games, BU Radio, and Glissando, with >500 speakers, 39,470 turn-final and 206,268 mid-sentence tokens across ~ 39,500 turns. Turn-final words are longer (mean ≈191 ms; d = 1.14). The effect persists in matched-word, within-speaker comparisons (80 ms; p < 0.001) and is localized mainly to the final syllable (d = 0.89). Turn-final lengthening thus emerges as a robust, localized cue to floor transfer.