Context Window on Programmer.ie: Modern AI programming

A Session Is Not a Stateless Function

Wed, 02 Sep 2026 15:00:00 +0100

A remote model API often encourages a simple mental model:

const answer = await complete(prompt);

Input goes in. Output comes back. Any conversation state is reconstructed by the application and sent again.

A browser-managed Prompt API session is a different kind of object. It owns resources, may retain conversational state, reports a finite input budget, supports branching in some implementations, and should be destroyed when its work is finished.

The correct abstraction is not a stateless function.

When the Context Window Fills

Wed, 02 Sep 2026 15:15:00 +0100

A stateful session eventually encounters a physical limit.

Prompts, initial instructions, examples, conversation history and model outputs all compete for a finite context budget. Once the budget is exhausted, the application cannot solve the problem by pretending the next message is independent.

The difficult question is not how to delete text.

It is how to preserve the right state.

1. The context window is a budget

When a session exposes usage and quota, context pressure becomes observable: