The Stripe payment .NET API has a generic class definition like below and I'd like to understand why the constraint part StripeEntity<T> should be the type T.
public abstract class StripeEntity<T> : StripeEntity where T : StripeEntity<T>
From: https://github.com/stripe/stripe-dotnet/blob/master/src/Stripe.net/Entities/_base/StripeEntity.cs
I understand the generic syntax, but don't understand why the class is defined in this way, the thinking behind it. Is this a common pattern around generic classes and if so what are the benefits?
It's called the curiously recurring pattern, usually used in C++.
It has a couple of things going for it, especially the fact that it's a (very limited) form of static polymorphism, and so avoids the costs of calling virtual functions. That has more value in C++ than in C# however, due to how the language and runtime are constructed.
.Net also has better ways of dealing with this, for example you could achieve something similar in a cleaner way by using attributes and source generators.