Channel binding not supported using scram-sha-256 passwords

I've been trying to implement scram-sha-256 passwords on PostgreSQL 11.1. However, connection attempts whether through Python (psycopg2) or psql fail with the message: "channel binding not supported by this build." I've tried clearing scram_channel_binding in my global psqlrc ("\set scram_channel_binding"), with no success.

We are not using SSL for the connections, and the documentation labels this as an SASL authentication mechanism. Is SSL required for using scram-sha-256 passwords? What am I missing?

Thanks,

Hugh