The Cosmos could be the successor to last year's Xperia C3, which is Sony's first (and only) smartphone to have a 5 MP front-facing camera with LED flash.
According to @upleaks, the Xperia Cosmos runs Android 5.0 Lollipop, and is powered by an unknown MediaTek processor. This would be Sony's third smartphone of 2015 to use a MediaTek solution, after the affordable Xperia E4 and E4g (both of which will be available in the near future).
The Xperia C3 (seen above) has a 5.5-inch 720p display, but it's not clear if the Cosmos sports a similarly sized display (or if it's a mid-range device, like the C3). Hopefully, it won't be long until we find out more about this new Sony Xperia.
The unannounced Sony Xperia Cosmos
source: @upleaks (1), (2)