Yes, the hub is identical
Same 5x112 PCD and same 66.5 mm centre bore: wheels from Audi A8 D5 bolt on and centre on Audi S8 without rings. You still need to check the offset and tyres, detailed below.
≈: width estimated from the original tyre size.
Wheel by wheel: offset and tyres
Each original wheel from Audi A8 D5 is compared with the one from Audi S8 of the same diameter: how much closer the wheel gets to the shock absorber or how far it sticks out of the wheel arch, and whether the tyre keeps the same overall diameter.
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8Jx17 ET29 · 235/60R17 — Check on the car
Compared with the original ≈7.5Jx17 ET40 on Audi S8: shock absorber side −4.7 mm, wheel arch side +17.4 mm, tyre diameter +5.5 % : fit it with the original tyre size of Audi S8 (245/50R17), not that of Audi A8 D5.
Comparison for guidance only (estimated width). Check in detail
Before fitting the wheels
An identical hub is not enough: offset, width and diameter change the position of the wheel, and larger calipers can touch a smaller wheel. Original wheels often use bolts or nuts with a specific seat: keep the fixings intended for the wheel, with the thread of Audi S8 (M14x1.50), tightened to the torque shown on its vehicle page. Finally, check that the size is among the approved fitments for your vehicle. This comparison is for guidance only: have the fitting approved by a professional.
And the other way round: wheels from Audi S8 on Audi A8 D5?