It appears that opcodes 2010 and 2011 were added for 3.2:

https://github.com/mongodb/mongo/blob/r3.2.0/src/mongo/util/net/message.h#L71-L72

And packet captures show those are by far the dominant opcodes in traffic to a 3.2 server, but they aren't documented at all in the Wire Protocol documentation:

https://docs.mongodb.com/manual/reference/mongodb-wire-protocol/

This makes it pretty hard to actually make sense of MongoDB network traffic. Could someone update it?