So the biggest difference I see is that ForwardRef._evaluate() has grown a recursive_guard argument in 3.9. This makes me think that in 3.8, only one level of evaluation was happening, and in 3.8, we keep evaluating until we don't see a string or ForwardRef.

The specific examples all happen at a point where the forward ref "C" cannot be resolved at all yet (since they're happening *in the class body*).

Possibly the best way out is to treat unresolved references differently, and just return the ForwardRef to the caller -- after all this is what the example does in 3.8.