# Models and Decisions

Choose who decides for a supported role. The world validates every proposal before it takes effect.

## Give a Model a Role

People, animals, vehicles, and other decision-makers can act in a world. A decision role is the subset a model may decide for.

The role registry supports a person and a junction signal. Discover the roles your world offers rather than assuming every agent can be assigned a model. Model-run vehicles, weather, and economies are product targets without supported role contracts.

**Routine**

Runs without model calls. Supplies a valid decision when a model or outside agent cannot answer.

**Chosen model**

Receives the role’s context and offered choices through the configured provider.

**Outside agent**

Answers offered turns under a grant issued by the world owner.

## Choose a Model

People follow their routines until you assign a model. Your installation determines which models are available and how many people one choice can cover.

1. Open the controls for the world’s people and select a model from Decided by.
2. Choose the people you want that model to decide for.
3. Select Use for the chosen people. The model takes over from their next decision.

![Four people selected under Decided by in the application.](/product/model-selection.jpg)

A recorded session assigning a model to a group. Available models depend on your installation.

The world checks each answer before applying it. An invalid or missing answer leaves the person with a valid routine decision. Inspect a person to see who decided their latest turn and the recorded reason.

## Follow One Decision

1. Observe. The role supplies context and the choices available at this decision point.
2. Propose. The model returns an offered choice within its answering budget.
3. Validate. The engine checks the proposal before applying it and records a refusal when it cannot apply.
4. Record. The observation, the model, and the result stay available for inspection and replay.

A provider answer is not proof that the world applied it. Inspect the recorded outcome and reason.

## Model Availability and Spending

The installation’s model catalog, role requirements, provider credentials and spending authority determine availability. Choosing a model does not prove its host is ready.

Live decisions call the configured provider. Replay reads stored decisions without another call. Configure your spending bound before starting a comparison.

[Installation](/docs/self-hosting#docs-self-hosting-models)

[List Decision Roles](/docs/world-api/models)

## Connect a Model of Your Own

Use Python or MCP to run an outside agent. The grant defines its subjects, expiration and permitted turns; your model runs outside the world and submits one offered action.

[Connect an outside agent](/docs/agents)

[Decision-role contract](https://github.com/twinkling-reality/exulanica/blob/main/docs/decision-roles-contract.md)