// Summary: // Use the default behavior for the host environment. For ASP.NET hosting, use // the value from the customErrors element in the Web.config file. For self-hosting, // use the value System.Web.Http.IncludeErrorDetailPolicy.LocalOnly. Default = 0,So now, with the default policy enabled, the ASP.NET host will look inside the custom errors element in the web.config by default, to determine whether it should include error details or not. This makes for the error detail behavior of Web API to always be consistent with the one of MVC and WebForms in the same application.
Those that have yet to have their first look at ASP.NET Web API will probably take this behavior for granted. But we will never forget.