Valve's trio of new titles - Episode Two, Team Fortress 2 and Portal - will be shown in real-time at the Leipzig Games Convention.
"We'll have a real-time demo of the games behind closed doors," Valve marketing director Doug Lombardi told Eurogamer last night.
"It will not be playable, but will be new, never-before-seen items."
Games Convention, which runs between August 24th and 27th, will mark only the second occasion Valve's shown its new toys off in the open.
Valve hopes to finish and release Episode Two, which will include TF2 and Portal as part of a bundle, on PC, PlayStation 3 and Xbox 360 this Christmas.