# Before Configuration Finalized


> [!CAUTION]
> `IWantToRunBeforeConfigurationIsFinalized` is deprecated starting in NServiceBus version 10. Refer to the [NServiceBus 10 upgrade guide](/nservicebus/upgrades/9to10/index.md#deprecated-iwanttorunbeforeconfigurationisfinalized).

During endpoint creation the configuration object used to construct the endpoint becomes frozen and locked. Classes that implement `IWantToRunBeforeConfigurationIsFinalized` are instantiated and called just before this happens. Use `IWantToRunBeforeConfigurationIsFinalized` for any last minute alterations to the configuration that may rely on other configuration settings.

Instances are:

 * Located by [assembly scanning](/nservicebus/hosting/assembly-scanning.md).
 * Created just before the configuration is frozen.
 * Created on the same thread that is creating the bus.
 * Created with [`Activator.CreateInstance(...)`](https://msdn.microsoft.com/en-us/library/system.activator.createinstance) which means they:
    * Are not resolved by [dependency injection](/nservicebus/dependency-injection/index.md) (even if they are registered there).
    * Will not have any dependencies injected.
    * Must have a default constructor.

Once instantiated, `Run(...)` is called on each instance. These calls are made on the same thread that is creating the endpoint.  The order in which instances are instantiated and run is non-deterministic and should not be relied upon.

Exceptions thrown by instances of `IWantToRunBeforeConfigurationIsFinalized` are unhandled by NServiceBus and will bubble up to the caller.

<!-- snippet: lifecycle-iwanttorunbeforeconfigurationisfinalized -->

```cs
class RunBeforeConfigurationIsFinalized :
    IWantToRunBeforeConfigurationIsFinalized
{
    public void Run(SettingsHolder settings)
    {
        // update config instance
        settings.Set("key", "value");
        // after this config.Settings will be frozen
    }
}
```

<!-- endsnippet -->