tl;dr: AutobahnPython is removing support for WebSocket Hixie76.
This old pre-standard WebSocket version isn't used anymore in the wild, has security issues and it does add a lot of cruft to our codebase.
AutobahnPython has implemented WebSocket for a long time and since the very beginnings of the protocol, when the final protocol specification (RFC6455) wasn't even existing.
These old protocol versions are called Hixie76 and Hybi10+, and most WebSocket users won't even know what I am talking about here;)
Those versions were implemented by years old browsers, e.g. Hixie76 was shipped with Firefox 4 (yes, that's 4 - the version I am using right now is 40) and RFC6455 is supported since Firefox 11 and Chrome 16.
See here for a history and browsers:
Hixie76 is very different from the final RFC6455. We are removing the code (some 800 lines) in AutobahnPython.
The WebSocket versions between Hybi10+ and RFC6455 are quasi identical apart from some minor differences in openening handshake aspects (HTTP header etc), and we will continue to support these.