Just to clarify for everyone here, since there seems to be a lot of uncertainty:
The issue (thus far) is only apparent when using your own api key
However, we have confirmed that the clouddrive keys are the exception, rather than the other way around, as for instance the web client does have the same limitation
Previous versions (also) do not conform with this limit (and go WELL over the 500k limit)
Yes there has definitely been a change at googles side that implemented this new limitation
Although there may be issues with the current beta (it is a beta after all) it is still important to convert your drives sooner rather than later, here's why:
Currently all access (api or web/googles own app) respects the new limits, except for the clouddrive keys (probably because they are verified)
Since there has been no announcement from google that this change was happening, we can expect no such announcement if (when) the clouddrive key also stops working either
It may or may not be possible to (easily) convert existing drives if writing is completely impossible (if no api keys work)
If you don't have issues now, you don;t have to upgrade, instead wait for a proper release, but do be aware there is a certain risk associated.
I hope this helps clear up some of the confusion!