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Why don't GPT-style tokenizers feed every English word as single letters?

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Answer: Sequences get too long

Words should stay intactKeeping every word intact sounds tidy, but natural language has endless names, typos, compounds, and new terms. Pure word tokens create an open-vocabulary problem. Subword tokenization is the compromise: common pieces stay compact, while unfamiliar words can still be built from smaller parts.

Sequences get too longA character-level input keeps every letter visible, but it makes the sequence much longer. BPE-style tokenizers compress frequent chunks, so the same context window can carry bigger pieces of text.

Characters are fasterCharacters feel simpler to humans, but they are not automatically faster for a language model. They create many more processing steps and burn through the context window sooner. The alphabet is tiny; the problem is the long sequence created when every paragraph is spelled out letter by letter.

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