# Cost Estimates

`llm_connect.costs` converts token estimates or observed token counts into
USD estimates using `ModelRateRegistry`.

## Contract

```python
from llm_connect import estimate_cost

estimate = estimate_cost("openai/gpt-4o-mini", 28_000, 7_500)
```

For known models the result is:

- `cost_usd`: prompt plus completion estimate.
- `prompt_cost_usd`: prompt-token component.
- `completion_cost_usd`: completion-token component.
- `cost_source`: `rate_table:<model_id>`.

Unknown models return `CostEstimate(cost_usd=None, cost_source="unknown")`.
Missing rates are never silently treated as zero cost.

The module also exposes `CostModel(registry=...)` for callers that prefer to
carry a registry object and call `model.estimate_cost(...)`.