Sony Ericsson just announced that the XPERIA Arc will be running Android 2.3 Gingerbread, but a prototype was caught in the wild that claims to have Android 2.4 on board. It appears that Google have another update in store for us before the tablet-ready Honeycomb comes.
Much like Android 2.0 and 2.1, which both carried the Eclair moniker, 2.3 and 2.4 will share the Gingerbread name. As you could imagine the differences between the two versions aren't too dramatic really, but the source claims that there's a notable performance improvement.
There are also some new animations, some new player application and noise reduction option in the call options. Some mysterious videochat option also appeared, but it wasn't enabled on that prototype. Have in mind that the guy that got to play with the new Android version only had about 15 minutes to spend with it so there might be more to Android 2.4 than we can tell you right now.
We'll see when the official Google announcement comes. With Honeycomb expected to be finalized in just a few months the Gingerbread preceding it should already be nearing completion.