What is a context window and why does it matter for coding AI?

The context window is the amount of text (measured in tokens) the AI can process at once. Larger windows mean the AI can see more of your codebase simultaneously — critical for understanding cross-file dependencies. GPT-4o: 128K tokens. Claude: 200K tokens. For a typical codebase, 100K+ tokens covers 50-100 files of context. Tools like Cursor and Claude Code manage context automatically, pulling in relevant files.