Token (Word Unit)

Have you ever wondered how AI understands your text when you ask Deepseek, Doubao, Qwen, ChatGPT, or Claude a question?

The core of the answer is something calledToken, which in Chinese is calleda word unitThe concept. Understanding Token is the first step into the AI world.

What is a Token (Word Unit)?

Token (词元) = AI 能理解的最小文本单位

We can think of it as: fragments of text in the AI world, or the fuel of the AI world.

Just as humans read by understanding meaning in word-sized units, AI doesn't process text letter by letter either—it cuts the text into pieces, and each piece is called a Token (word unit).

A helpful analogy:

Imagine an article as a pizza. You wouldn't swallow it whole or grind it into powder—you cut it into slices, and each slice is a Token. That's how AI consumes text: cut, understand, digest.

Token is finer than a word and coarser than a letter—a flexible intermediate unit.

What does a Token look like?

Different texts are segmented in very different ways.

Common words are one Token, complex words get split, and punctuation counts as a Token too.

TokenandCharacter、 wordWhat's the difference?

Many people think Token = word, but in factit's not entirely true.。

Token segmentation follows a special algorithm (such as BPE, Byte Pair Encoding), and the results are sometimes intuitive, sometimes surprising:

Conclusion:Tokens are finer than words and coarser than letters, serving as a flexible intermediate unit.

Why Does Token Matter?

1. It determines how much AI can read

Every AI model has aContext Window, which is the maximum number of tokens it can process at once. For example:

• GPT-3.5: about 4,000 tokens
• GPT-4 Turbo: about 128,000 tokens
• Claude 3.5: about 200,000 tokens

Beyond this limit, AI will fail to remember what was said earlier, just like when a person's short-term memory is full.

2. It affects API usage costs

When calling an AI interface (API), fees are usually charged based on the number of tokens.Input text + AI's response text, both consume tokens, so the longer you write, the more it costs.

3. It affects AI response speed

When AI generates text, itoutputs one token at a time.Therefore, the longer the reply, the longer the waiting time.

Token Trivia

• 1,000 tokens ≈ 750 English words, which is a commonly used estimation ratio.
• Chinese, Japanese, Koreanand other Asian languages usually consume more tokens than English because these characters are more complex in encoding.
• Spaces and punctuationalso count as tokens! Don't think only text counts.
• CodeThe token consumption of code is generally less than natural language because programming languages are structurally compact.

Summary