Stateful

A stateful system remembers. Within a session, your coding agent is stateful: what you said in turn one still shapes turn twenty, because the harness keeps the transcript and sends the accumulated history with every request. That statefulness is manufactured. The model receives the whole history each time and reconstructs 'what we were doing' from scratch; it just does so reliably enough to feel like continuity.

Across sessions the default flips back to stateless. Making an agent stateful over days and weeks means adding a layer that writes things down and reads them back: project instruction files, a memory system, notes it leaves for its future self. Where that layer is thin you get the familiar symptom of re-explaining your architecture every morning.

Statefulness has a cost as well as a benefit. Everything the session retains occupies the context window and competes for the model's attention, so a session that remembers everything also gets slower and vaguer. The useful stance is selective: make the state that matters durable in files, and let the rest expire with the session.