Annual servicing all day long, but certainly every 10k miles. Audi moved to long service regimes because they were shifting cars with finance and offered free servicing as an incentive. They also introduced it to seduce fleet dealers who hoped to reduce their running costs. The whole thing is a fallacy. The reality is no synthetic oil can retain the lubrication properties to protect an engine after 18k miles. Down the line, an unsuspecting new owner will buy an ex-fleet or leased 3-4 year old car and discover premature engine wear and pick up the bill. For all the costs of an oil filter and 5-6 litres of fresh oil, just change it. I personally do it every 5k miles, still use Castrol Edge 5w30 LL, but my 2017 plate 3.0 TDI Allroad will be my last diesel.