3D to 4D: Sudden or Gradual? A great read...(David Wilcock interview)

[Parsons]

This seems quite clear to me.

And that is that it is likely that this lifetime or at the very most, for those who die soon from the physical body, one more lifetime, shall be the last opportunity before graduation to refine the polarity of self to the point at which you the seeker might accept the quality of light which is the native light in fourth density...

... ...It is difficult but not impossible to predict with any accuracy what shall occur with your people. However, the time of third density for doing third-density work is virtually over...

It depends on which parts of the quote you are paying attention to / highlighting. After reviewing almost the entire Q'uo material, I can very confidently say that you could come to a conclusion that the transition to 4d will be a gradual one OR you could come to the conclusion it will have an abrupt switchover moment. I have noticed, however, in most of the quotes provided for a gradual transition stem from a fearful question being posed about the end of 3D. Point in case:

Group question: The question today, Q’uo, has to do with information that you gave some time ago concerning the end of third density and the beginning of fourth density. We’re wondering if there is any reason for us to be afraid of anything that’s going to occur then. Everything that we know is going to come to an end, as we know it, in third density. An entirely new fourth-density vibration is coming in, entirely new ways of looking at things, of doing and being. Is there any reason for fear?

Answer:

...One reason there is no need to fear these changes is that these changes are largely non-physical. As the questioner expressed the question, it was clear that the questioner was aware that they take place in the unseen realms, the inner planes. Therefore, while these changes are absolutely radical and revolutionary, they are not changes that will affect life as you know it on planet Earth. Consensus reality shall reflect only shadows of these changes...

Nowhere does Q'uo correct the question being posed and say that 3D isn't coming to an end(for this planet).