If they run constant constant fuel rate, varying the boost to maintain a constant lambda then when they shift up they need to very rapidly increase boost, by maybe 0.5 bar. There are a number of inertias to overcome to achieve this so I wonder if they increase boost as a shift approaches, running a little leaner, perhaps sacrificing power for driveability. This might be particularly useful if the upshift occurs in a corner when they could target having the same power immediately before and after the shift.
In the data of Ferrari at Singapore the time in 7th gear is less than 2 seconds. I have previously done some calculations on the acceleration rate for the TC MGU-H assembly. With a driving power of 150kw I found an acceleration rate of 6000 rpm/sec. I would guess that this is in the ballpark for a change of 0.5 bar. So managing lambda with boost, particularly through upshifts may well involve quite a few compromises.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus