As is often the case with smartphone leaks, the first one opens the floodgates to a wave of others. It looks like Google's next Nexus device, which most are calling the Nexus 5, will be no different. As discovered by S4gru, a smartphone manufactured by LG has appeared on the FCC's site with enough detail to associate it with the device that Google itself leaked in a KitKat promo video earlier in the week. The documents include a photo of the inside of the rear cover and its dimensions, including a very large hole for the camera, match up quite well. Unfortunately for people who need to swap batteries, the back is "not supposed to be removed."
More importantly, as Engadget notes, this device is being tested for a wide array of wireless standards, including support for LTE that should work on AT&T, T-Mobile, or Sprint. It also supports the usual set of HSPA and GSM bands along with CDMA and EVDO Rev A. If this device pans out, that will mean that Google will have finally righted the wrong it made with the Nexus 4 — namely putting proper support for LTE on its flagship Android phone. With both T-Mobile and AT&T accepting unlocked devices on their LTE networks, it only makes sense.
As for other specs on this device, all we know for sure it that it looks significantly larger than the Nexus 4. With that device selling out in the US Google Play Store and Google revealing the new name for Android 4.4, it's not a small jump to assume that this purported Nexus 5 will be announced fairly soon.
Update: As commenter Alketi notes below, one of the FCC documents reveals some additional details. The device is listed as having a 4.96-inch screen, and will run 5.19 inches in height and 2.69 inches in width. A 2,300mAh battery is also noted in the documents.