Decoder. plain-English AI glossary

Sequence length

● Core

How many tokens are actually in a given input or output right now.

Think of it like

The number of cars in the train you’re running today, versus how long the platform can hold.

Example

A 500-token prompt has a sequence length of 500, well under a 128K context limit.

How it actually works

Sequence length is the count of tokens being processed in a specific pass, while context length is the ceiling. Attention cost grows roughly with the square of sequence length, which is why long inputs get expensive fast. Keeping sequences tight is a real performance lever.

For product teams

Shorter sequences mean lower latency and cost — trimming inputs is a cheap optimization.

For engineers

The token count n of a given batch element; attention is O(n²) in it.

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