The first HTC One M9 concept was made by Hasan Kaymak, and seems to propose a device without BoomSound speakers. This allows the display to occupy a very large portion of the handset’s front. The smartphone should come with Sense 7 UI (which doesn’t exist yet).
The second HTC One M9 concept is more detailed, including some specs. Made by Rishi Ramesh, this imagined One M9 offers a 5.2-inch Quad HD display, 3GB of RAM, a 13MP Duo rear camera with 4K video recording, 7MP front-facing camera, and a 3,000 mAh battery.
Take a look at the two concepts and let us know if you think they're close (or not) to what HTC may be preparing for next year.
sources: Google+, GatgetsConcept via Concept Phones