Stateful

Carries information forward. A session is stateful across turns — context accumulates as the session runs, which is why long sessions drift into the dumb zone. An agent can be made stateful across sessions by adding a memory system that persists information into the environment and reloads it at the start of future sessions. The model is never stateful; any apparent continuity is the harness re-feeding context. Counterpart to stateless.

Where state lives at each layer:

Layer	Stateful?	How
Model	Never	Parameters are frozen; it sees only what's in each request
Session	Across turns	The harness appends every message and tool result to the context
Harness	Across sessions	Memory files, AGENTS.md, handoff artifacts — written down, reloaded later
Environment	Always	Files persist whether or not any session is running

Each layer's statefulness is built by re-reading something stored a layer below: the session feels continuous because the harness re-sends the message history to the stateless model, and the agent remembers across sessions because the harness re-loads files from the environment. No state is ever stored in the model itself.

State isn't always wanted. Everything carried forward influences what comes next, so a wrong assumption made early in a session is carried forward too. Clearing is the deliberate act of throwing session state away and starting from what's written down.