The level designer Benoir Deschamps, currently working on Rainbow Six: Siege, said in a recent interview that the stock has ten maps at launch.
However, he stated that they are already thinking of the content to be published after the exit of the title in the shops, then surely we will see the introduction of new maps over time.

We remember that the start of the beta of Rainbow Six Siege is waiting for September 24, while the full version of the product will be available for the Windows PC, Microsoft Xbox and Sony Playstation 4 One from next December 1st.

Please note that you can read a hands on the title by the editorial department at the following address.
Stay tuned for the latest news on this interesting tactical shooter from Ubisoft.