Pretraining Explained: How an AI Model Learns Before Anyone Teaches It

Business Pill 23 · How a model learns before it has a job

Before it has any job, a model learns by playing one simple game trillions of times: guess the next word. That stage is called pretraining.

A short explainer video. The numbers in it are round numbers for illustration.

The Short Answer

Before anyone teaches it a task, a model plays a simple game. Take a sentence, hide the next word, and ask the model to guess it. Then show the real word and adjust the model a little, so its next guess is better.

Trillions of Guesses

Now repeat that game trillions of times, across books, websites, code and conversations. Nobody labels anything. The text itself provides the answer. That is what makes it possible at this scale.

To guess well, the model has to pick up a great deal along the way: grammar, facts, how an argument is built, how code works. None of it is taught directly. It all comes from predicting the next word.

The Expensive Stage

This stage is called pretraining. It produces a general model, one that knows a lot but has no particular job yet. It is also the expensive stage: thousands of chips running for months. Very few organizations can afford it.

But it is done once, and the result can be reused for thousands of different purposes. This shapes the whole industry: a handful of companies build the general models, and everyone else builds on top of them.

Why It Matters

A model only knows what was in its training text, up to the day that text was collected.

Three Questions to Ask

  1. What text was the model trained on?
  2. When does its knowledge end?
  3. What does it still need to learn for our work?

How This Concept Connects

Layer 2 of 8 · Models & Training, on the Business Engineer Concept Map

  • Pretraining builds on Parameters. Pretraining nudges the model a little after every guess, and those adjustments are the parameters the dials lesson describes.
  • Pretraining contrasts with Data Labeling. Pretraining needs nobody to label anything because the text supplies the answer; data labeling needs people to attach answers.
  • Knowledge Cutoff builds on Pretraining. A model knows only its training text up to the day it was collected, which the cutoff lesson names as the knowledge cutoff.
  • Fine-Tuning builds on Pretraining. Fine-tuning is extra training on your own examples, applied on top of the general model pretraining produces.
  • RLHF builds on Pretraining. RLHF starts from a model that learned to continue sentences by reading enormous text, then trains it toward helpful answers.
  • Inference contrasts with Pretraining. Pretraining is the expensive stage paid once; inference is paid on every answer, small and forever.
  • Temperature builds on Pretraining. Temperature sets how much chance the model allows when picking the next word, the guessing game pretraining teaches.
  • Physical AI (lesson unlocks soon) builds on Pretraining. The new robots learn the way chat models did, from enormous numbers of examples, rather than following a fixed script.
Business Engineer framework
AI Quality Plateau
Pretraining scale is what the quality-plateau debate is about.
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