Level 3 · Unit 1 · FreeInside the models
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Pretraining: where a model’s knowledge comes from

Every large language model starts with . It reads a vast amount of text, such as web pages, books and code, and practises one task: predicting the next . After each guess, its internal numbers are nudged towards the right answer.

At enormous scale, this builds grammar, facts, styles and reasoning patterns, plus the text’s errors and stereotypes. Its knowledge stops where the data ends.

It’s so costly that few organisations do it: you’ll almost always start from someone else’s model.

  1. Read“Put the kettle on and make a cup of…”
  2. PredictIt guesses “coffee”
  3. CheckThe real text says “tea”
  4. AdjustIts numbers shift towards “tea”
One step of pretraining, repeated an enormous number of times.