I dont recall my medium's top and down tubes coming together like the one in the photo. But its a couple fo months since I last used it.
The acid test is to measure it. 50cm from centre bb to top of seat collar for a medium.
This is my Medium. It looks a bit different now but you can see that the top and down tubes are separated by a length of head tube. I'm pretty sure it's basically the same frame as the ONCE model shown, just a different size.
The pic is just for the model year I'm asking about, it isn't the bike I'm measuring. I did have one of these a few years ago in medium and it fit me perfectly. I've since forgotten the TT size and couldn't seem to find any mention of it anywhere. Since then Giant have changed their geometry and I wasn't certain if the modern ones were the same.
55.5cm seems to ring a bell though.....
I just needed the measurement to make sure the bike I'm looking at will be comfortable for me (I use TT length to size a frame, not ST length).
BTW I originally put this in "Off Topic" as I didn't think that the bike was retro.