The current version of the BLXR Protocol is Version 8. The bloXroute BDN currently supports BLXR Protocol Versions 6, 7, and 8. Gateways announce the version of the protocol they are running during an initial HELLO Message. Relays will always run the latest version of the protocol and will know how to convert from older versions of the message to the latest.
For example, if the latest version of the BLXR protocol is Version 8 with support of Versions 6 and 7, each Relay will know how to convert 6 -> 7, 6 -> 8, 8 -> 7, 7 -> 6. If a Relay receives a message from a Gateway running Version 6 then it will convert the message to Version 8 and broadcast the message of Version 8 across the BDN. Likewise, when another Relay sends that message to a Gateway running Version 6, the Relay will convert the message from Version 8 to Version 6, and send the Version 6 message to the Gateway.