arXiv Computation and Language By Tanja Baeumel, Josef van Genabith, Simon Ostermann

When Tokenization is Secretly Output Supervision

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The paper argues that tokenization in language models should be viewed as an output supervision decision rather than merely input preprocessing. In autoregressive models, the granularity of the tokenizer determines the supervision signal the model receives, influencing learning difficulty, internal representations, and task performance. Experiments on numeric reasoning show that output tokenization, rather than input tokenization, drives differences in performance and training dynamics, and a survey of recent CL papers reveals that tokenization choices are rarely reported or acknowledged.

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