Hello Alex,
After 8.3.1 the licenses are shared between the two boxes.
Before that version you will need to run different ( but the same) licenses on both ASA's.
Now if you have licenses already on both devices they are combined.
Hope I was clear
Julio
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Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC