When upgrade from BW 3.5 to BW 7.0, how to reuse BEx 3.5 OLAP query

One of my customers are upgrading from BW 3.5 to BW 7.0, their question is

Can they call BEx 3.5 having existing OLAP queries with BW 7.0 ?

Or is it mandatory to migrate BEx 3.5 to 7.0 adapting APIs ?

Thanks a lot in advance!