Yesterday, Kotaku received a press release confirming that Rockstar Games will be present at next week's Games Convention in Leipzig.

Rockstar Games is happy to announce its attendance at the GC in Leipzig, Germany this August. Two upcoming titles will be on display at the conference, including the world-wide unveiling of Rockstar's newest installment of the Midnight Club franchise, Midnight Club Los Angeles. Be among the very first in the world to see the game as live demonstrations happen throughout the day on the show floor. Also appearing at the show is the Wii version of Rockstar's award-winning title, Rockstar Games Presents Table Tennis, which will be available to the public in hands-on form.

They don't mention GTA IV specifically, but look at this picture posted on the official Games Convention blog:

What this probably means is that Rockstar will be showing (in private) the latest build of GTA IV to gaming magazines for the next round of previews - but don't mark my word on that, the truth is it could be anything.

(UPDATE) A second picture from the blog...

Related Link: GTAForums Topic