Night train-- Oslo to Stockholm

I read in Rick's book on Scandinavia that there's a 9-hour direct night train from Oslo to Stockholm in summer only. But I'm not seeing it on any of the timetables. The latest train I'm seeing for August 2nd is 15:46. Is it possible that the night train is sold out and that's why I'm not seeing it? If so, how can I find out? Or is it too early to book the night train? thanks.