This is not an A/B test, we’re just rolling it out slowly because this is a large change.
We are moving from chat to self-serve for the majority of cases (some will always require you to talk to a human because the case is too complex for a form), not testing the two at once.
At the scale Monzo is now, if we turned anything on to 100% of users at once and it caused errors, we would risk causing large scale impact and support overload. As a result, we tend to start with a small launch and increase the rollout as we’re comfortable that it is working as expected. 
It is worth noting that the questions you’ll be asked are the same questions customer service will ask. You’ll just be able to answer them and get on with your day while your answers go directly to the Disputes Operations team instead of waiting for your chat to be answered and escalated to them.