Before it
Production context windows were 4K to 8K tokens, occasionally 32K.
The problem
Anything book-length had to be chunked and retrieved rather than read.
What it introduced
A deployed 100,000-token window, enough for a novel or a large codebase in one prompt.
Why it matters
It opened the long-context era in products and began the running argument about retrieval versus a bigger window.
What modern models inherit
The expectation that a model can read a whole document.
What came next
Gemini 1.5's million tokens, and the long-context race through 2026.