Microsoft.Extensions.Options provides a strongly typed way of specifying and accessing settings using dependency injection and acts as a bridge between configuration, DI, and higher level libraries. This library is the glue for how an app developer uses DI to configure the behavior of a library like HttpClient Factory. This also enables user to get a strongly-typed view of their configuration.
Documentation can be found at https://learn.microsoft.com/dotnet/core/extensions/options.
Although the types are mature, the code base continues to evolve for better performance.
Microsoft.Extensions.Options is not included in the shared framework. The package is deployed as out-of-band (OOB) and needs to be installed into projects directly.