Finding latest production version for a major release

gistfile1.txt

var repo = PackageRepositoryFactory.Default.CreateRepository("https://www.nuget.org/api/v2/");

var pkg = repo.FindPackage(packageID,
   new VersionSpec
                {
                    MaxVersion = new SemanticVersion(4, 0, 0, 0),
                    IsMaxInclusive = false,
                    MinVersion = new SemanticVersion(3, 0, 0, 0),
                    IsMinInclusive = true
                }, false, false);

Console.Out.WriteLine("version={0}", pkg.Version);

Thanks @emgarten