Cisco CUBE - maximum SIP sessions

Just trying to get my head around what Cisco mean by a session.

The below link:

https://community.cisco.com/t5/ip-telephony-and-phones/how-many-calls-handle-by-cube-gateway/td-p/3059971

States that ASR 1001-X does 12k sessions, but does that mean 12k calls, or 6k? im not sur if their figures are uni-bidirectional or if they mean 24k active "legs" (2legs per call)