Developer 29Palms Scenery Design announced shortly before the release of P3D V4 what plans they had for the new 64bit sim.
Samos, Magdeburg and Twentynine Palms have been updated and are fully compatible with P3D V4. If you have already purchased the sceneries then you can download the new installers free of charge here.
In case you have previously purchased the sceneries at other stores than at Aerosoft or SimMarket, it might take a while until they fully upload these new installers for the airports. Both resellers has been notified.
Be aware that 29Palms has completely dropped their support for P3D V1 and V2. Their sceneries will continue to work and you will get updates as well but new installers will not support P3D V1 and V2 anymore.
Here are a few screenshots of both Samos and Twentynine Palms and by judging them it looks awesome.