The API has not changed, however the behaviour is slightly different. Session and time limits are taken into account when ads are created, which means that the static helper methods for creating them can now return null. As such all the InterstitialAd and RewardedAd objects should be null-checked after creation.
With these changes you can now adapt your UI in case of providing the user with a reward, for example hiding the option in the UI if a rewarded ad is not currently allowed to be created and showing it in the other case.
For more details see here.