coin acceptance is mechanical - how could it be software? You are physically putting coins in a physical slot.
I wondered how long this thread would run before anyone considered how the machines work!
I don't think anything, other than the basic stuff like shopping trolleys and parking meters, has used mechanical gauging for many years. Certainly the latest ones rely on optical, magnetic, and electromagnetic sensors. There's an example
here. That refers to 3 inductive sensors, 1 optical sensor and 1 magnetic sensor, measuring 10 different parameters regarding frequency, dimensions and phase.
That's why coins have, for ages, been made with carefully chosen alloys, to vary those properties. More recently we have coins made of more than one alloy in different parts, for the same reason. This new pound coin has some fancy internal feature that the Royal Mint are being coy about, presumably in the internal arrangement of the two (or more) alloys.
So all of that is in principle a "software only" change. However, I suspect that something new (like this £1) might need a redesigned sensor. Of course not every machine has to sense every detectable feature, but
TVMs▸ are at the high-value end of slot machines.
Coin recognition can be done as they fall into a bin. On the other hand, coin handling, and change dispensing, I suspect do need mechanical handling designed for the coin sizes. But I don't know whether TVMs need to recycle change, or can rely on just what's manually put in - that would be simpler.