One of the issues in the BSON 5 epic was RUBY-2993, which changed the behavior in Mongoid by adding for a compatibility flag, so that BSON::Decimal128 deserialization could behave as it did under BSON 4. We need to make sure that the backported version of that change (see MONGOID-5630) is applied and new versions of Mongoid 8.0.x and Mongoid 8.1.x are released, before we release BSON 5.