The first title revealed to be renumbering as part of Marvel Comics' line-wide "Legacy" initiative is the current series Ultimates 2. According to a listing on Marvel Comics' website database, August's Ultimates 2 will be numbered as Ultimates 2 #100 - taking into account all the various itterations of the "Ultimates" title going back to its 2002 Ultimate Universe launch by Mark Millar and Bryan Hitch.
Ultimates 2 #9 is scheduled for release in July 2017.
Venom is being renumbed to #150 with this week's issue, but according to Marvel is unconnected to its "Legacy" branding.
The publisher has not disclosed any further details about the title, or any other titles that will take part in the "Legacy" renumbering.