I am building new rpc api which by rule should be async but if this does not have any IO call today then i can not add await in the async method.
I do not want to make sync API today based on the current requirement as it may change later, later I may want to add IO call in the API which will end up blocking the thread if I make sync API today.
Question: Is there a recommended pattern to create async method without any await call in it?
If you mean you want the API to support async later, but you don't have any async operations today: that's fine - you can still just return Task / Task<T> and use Task.FromResult / Task.FromException. if you want to avoid the object overhead: ValueTask / ValueTask<T> work similarly, but the caller has some additional demands (specifically: to access the result exactly once).
You could also just suppress the compiler warning about missing await.