AFAIK, Surface Pro comes with DisplayPort but not Thunderbolt: these were the rumors around its presentation times and pictures seemed to suggest that was the case. But, who can tell (yet).

Edit:
Actually, specs from www.surface.com do mention MiniDisplayPort but not Thunderbolt (x86). That sounds somewhat "official" to me. I doubt specs will change for the better as we get closer to release.
Personally, that's too bad. With Thunderbolt and related expansion possibilities, that would have been almost my ideal tablet.