Google has just started rolling out the new XE11 update to Google Glass units, and the system image is already online and available for tinkering. Just head on over to the Glass developer site to download the newest image and rooted bootloader, if you're into that sort of thing.
The XE11 system image is just shy of 350MB, and the only other version available now is XE10. A change to the way Glass works with XE10 means you can't flash an earlier version without bricking the device. Altering the firmware will, of course, void the warranty and might prevent you from getting OTA updates.
With all those new Glass explorers about to get into the program, developer interest might be higher than in the past. Hit the link below to start messing around yourself. Be careful, though. You wouldn't want to break that $1500 face-computer.