Unless it doesn't want you to see it coming

Which requires likely using substantially slower speeds and also requires that every single AI coming in our direction has made that same decision.

or has swept past Earth already and left a false-sky planetarium in its wake.

This seems extremely unlikely. It first requires an AI to want to care enough to deceive us at the cost of pretty high energy levels and it requires his AI to use an extremely complex deception. The most obvious deception (and most likely form if one had occurred any time other than very recently) would be to simply make the sky look empty of stars. Not only that, but this apparent false sky has uneccessary details which would be extremely hard to fake, such as neutrino bursts from supernova. Note also that if there is such a false-sky planetarium then all the data we are using to discuss the Great Filter becomes complete suspect anyhow (because the AI could have deliberately made cosmology look very different than it actually is), so this essentially should fall into the same category as any highly deceptive, nearly omnipotent being.