Tokens, training, and inference: what happens when you hit enter

Step 1: tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → (how the model reads)

A large language modellarge language modelA Large Language Model is an AI system trained on vast text data to predict and generate language, enabling tasks like writing, summarizing, and answering questions.Voir la définition complète → (LLMLLMA Large Language Model is an AI system trained on vast text data to predict and generate language, enabling tasks like writing, summarizing, and answering questions.Voir la définition complète →) does not read words the way you do. It breaks text into tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →: small chunks that are often whole words, but sometimes pieces of words.

Here is the classic surprise. The word "strawberry" is not one unit to the model. It is usually read as something like "straw" + "berry." This is why models historically struggled to count the letters in "strawberry": they never saw the individual letters, just the chunks.

A rough rule of thumb in English: 1 token is about 4 characters, or roughly 3/4 of a word. So 100 tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → is about 75 words.

Some quick examples of how text splits:

• "cat" → 1 tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →
• "unbelievable" → "un" + "believ" + "able" (3 tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →)
• "GPT-4" → "G" + "PT" + "-" + "4" (several tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →)
• A space before a word is usually part of the tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → (" France" is different from "France")

You can see this for yourself with OpenAI's free Tokenizer tool. Paste in a sentence and watch it split into colored chunks.

Why tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → matter to you

TokensTokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → are the unit of pricing and limits. When a tool says it has a "200,000 tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → context windowcontext windowThe context window is the maximum amount of text (measured in tokens) a language model can process at once, including both the input prompt and the generated output.Voir la définition complète →," it means roughly 150,000 words can fit in a single conversation. When an APIAPIApplication Programming Interface: a standardised interface that lets applications communicate and exchange data without knowing each other's internal workings.Voir la définition complète → charges "$3 per million input tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →," it is counting these chunks, not words.

Practical takeaway: shorter prompts cost less and fit more. And odd behavior with spelling, rhyming, or counting letters often traces back to tokenization.

Step 2: training (how the model learned)

Before you ever typed anything, the model went through training: a long, expensive process of learning from enormous amounts of text (books, websites, code, articles).

The core task is shockingly simple. The model is shown a sequence of text with the last tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → hidden, and it must predict the next token.

Show it "The sky is" and it learns to predict "blue." Show it "2 + 2 =" and it learns to predict "4." Do this across trillions of tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →, billions of times, and the model slowly adjusts its internal settings (called parameters, the numbers it tunes) to get better at guessing.

Nobody hand-coded the rule "Paris pairs with France." The model saw that pattern millions of times in its training text and learned the statistical link on its own.

Two phases you should know

Training has two main stages:

1. Pre-training: the model reads the giant pile of text and learns next-tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → prediction. This produces a "raw" model that is knowledgeable but not very helpful or polite.

2. Fine-tuning and alignment: humans and automated feedback teach the model to follow instructions, be helpful, and avoid harmful answers. This is what turns a text-predictor into ChatGPT.

This is also why models have a knowledge cutoff. Training happened at a fixed point, so a model may not know about events after that date unless it can search the web. In 2026, ChatGPT, Claude, and Gemini all offer live web search to patch this gap, but the base knowledge is still frozen at training time.

Step 3: inference (what happens when you hit enter)

Inference is the moment of use: the model is done learning and is now making predictions for you in real time.

Here is the full sequence when you press Enter:

1. Your prompt is split into tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →.

2. The model reads those tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → and predicts the most likely next token.

3. It adds that tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → to the sequence, then predicts the next one.

4. It repeats, one tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → at a time, until it decides the answer is complete.

That word-by-word streaming you see in the interface? That is literally the model generating one tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →, then the next, then the next. You are watching inference happen live.

Why you get different answers to the same prompt

If the model always picked the single most likely tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →, it would be repetitive and robotic. So there is a setting called temperature that adds controlled randomness.

• Low temperature (near 0): predictable, focused, repeatable. Good for factual tasks, code, data extraction.
• High temperature (near 1 or above): varied, creative, surprising. Good for brainstorming, story ideas, marketing copy.

This is why asking "give me a tagline for my coffee shop" twice gives two different taglines. The randomness is a feature, not a bug.

Seeing inference in code

If you want to watch the pipelinepipelineAll active sales opportunities across the stages of the sales process, together with their combined potential value and probability of closing.Voir la définition complète → concretely, here is a short, runnable example using the OpenAI APIAPIApplication Programming Interface: a standardised interface that lets applications communicate and exchange data without knowing each other's internal workings.Voir la définition complète →. (You need an APIAPIApplication Programming Interface: a standardised interface that lets applications communicate and exchange data without knowing each other's internal workings.Voir la définition complète → key; the same idea works with Anthropic's Claude and Google's Gemini APIs.)

Two things to notice. temperature=0 tells the model to play it safe and pick the most likely continuation. max_tokens=5 caps the response length in tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →, not words, which ties straight back to Step 1.

Putting it together: the full pipelinepipelineAll active sales opportunities across the stages of the sales process, together with their combined potential value and probability of closing.Voir la définition complète →

Let's trace one real prompt end to end. You type:

> "Summarize this email in one sentence: [pastes a long email]"

1. TokensTokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →: your instruction plus the whole email gets chopped into tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →. A 500-word email is roughly 650 tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →.

2. Training (already done): the model long ago learned what "summarize" means and how summaries are structured, from countless examples.

3. Inference: the model reads all those tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → and generates a one-sentence summary, one tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → at a time, until it hits a natural stopping point.

No lookup. Just very, very good next-tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → prediction, shaped by training and powered by inference.

Why this mental model makes you better at AI

Once you see the model as a next-tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → predictor, a lot of practical advice clicks into place:

• Give context up front. The model predicts based only on the tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète → in front of it. If you don't paste the email, it can't summarize it. There is no hidden memory of your files.
• Examples steer predictions. Showing the model two sample summaries in your preferred style nudges it toward predicting that same style. This is why "show, don't just tell" works so well in prompts.
• Be specific to narrow the guesses. "Write a tweet" leaves the prediction wide open. "Write a 280-character tweet, friendly tone, one emoji, no hashtags" sharply constrains what comes next.
• Hallucinations are over-confident predictions. When the model invents a fake source, it is predicting text that *looks* right based on patterns, even though it isn't true. That is why you verify anything that matters.

For a deeper but still readable explainer, the Wikipedia article on large language models is a solid, free reference that stays reasonably plain.

Key Takeaways

• The model reads in tokens, not words. Roughly 4 characters per tokentokenA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →. This drives pricing, context limits, and quirks like miscounting letters in "strawberry." Try the Tokenizer tool once to make it concrete.
• Training is next-token prediction at massive scale. The model learned patterns like "Paris → France" by guessing the next chunk across trillions of tokenstokensA token is the basic unit of text that language models process, often a word fragment, whole word, or punctuation mark rather than a single character.Voir la définition complète →, not by memorizing a fact database.
• Inference is what runs when you hit Enter: one predicted at a time, streamed back to you. The live word-by-word output is the prediction happening in real time.