Is services.AddSingleton<IConfiguration> really needed in .net core 2 API

As the official roadmap for ASP.NET Core 2.0 says:

An IConfiguration instance will be added to the services container by default in ASP.NET Core 2.0, so that all applications can easily retrieve configuration values via the container

So services.AddSingleton<IConfiguration> (or similar) is already called by the framework itself.

You may see this behavior inside WebHostBuilder.cs file or (when using the utility extension methods) inside HostBuilder.cs file.