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Interactive sample · How ChatGPT actually works, an article

How ChatGPT actually works · Article

How ChatGPT actually works · 12 min read

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How ChatGPT actually works · Article

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  1. 1 Read ChatGPT writes one word at a time §2
  2. 2 Try Turn up the temperature §3
  3. 3 Quiz Same prompt, temperature 0 §3
  4. 4 Read How words become numbers §5
  5. 5 Try Find words that sit close together §5
  6. 6 Quiz Explain it in one sentence §6

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Back to course Step 1 · ChatGPT writes one word at a time

2. One word at a time

Here's the surprising part. ChatGPT never plans a whole answer. It looks at everything written so far, predicts a single next word, adds it, and then does the same thing again.

So a long, thoughtful reply is really thousands of tiny guesses in a row, each one shaped by the words that came before it.

That's also why it can sound sure and still be wrong: it picks the words that are most likely to come next, not facts it has checked.

4. Tokens

A token is a chunk of text the model reads as one unit: often a whole word, sometimes just a piece of one. "Unbelievable" might become "un", "believ", and "able".

Before any prediction happens, your text is split into tokens, and each token is turned into a long list of numbers. Those numbers are the only thing the model ever actually reads.

Next, we'll see how those numbers let the model notice which earlier words matter most, an idea called attention.

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Next-word prediction

How ChatGPT actually works · article

What it is

ChatGPT writes one word at a time, always picking a likely next word.

Why it matters

Every answer is thousands of small guesses, which is why it can sound sure and still be wrong.

Example from the source

“The cat sat on the…” → mat 62%, floor 18%, couch 11%.

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