Update 3: The 8.1 update is live as our T-Mobile Lumia 925 now has Lumia Cyan (and it is also enrolled in the Preview for Developers program)
Evidence comes from T-Mobile's support forums, which detailed the over-the-air update. However, that page has since reverted and despite an earlier claim, we have not had an update for our Lumia 925s. It looks like T-Mobile may have jumped the gun a bit early, although we have all the details.
In a screenshot sent to us, the original T-Mobile page claimed the following:
"Beginning October 28, the Lumia 925 received a software update to Windows Phone 8.1 / Software version 01061.00074.14391.37104. This update provides features and improvements: Windows Phone 8.1 and Inflight Texting support."
The update comes in at 267 MB.
As of 3PM ET, none of our T-Mobile Lumia 925s has received an update, and the support page has since returned to the original version from February 20. However, due to the amount of detail present in the original posting from the support forums, it should be clear that this update with Windows Phone 8.1 and Lumia Cyan is very, very close. Indeed, a few users are reporting updates coming in, meaning this could be the start of the update.
Stay tuned, as Windows Central will let you know if the update is finally available.
Source: T-Mobile; Thanks, Kurt D., for the tip and screenshot!