The HTC One (M7) went on sale last year in March, and it looks like its successor, the HTC M8 (HTC One 2?!) will start being sold in March of this year, too (the end of Q1 2014). The phone should be available on all four major carriers in US, although we don't know yet if it will launch on all of them at the same time, or it will be a staged roll-out, depending on what kind of deals HTC made with the carriers.
It will be interesting to see if HTC actually names it the HTC One 2, which would sound pretty weird, especially to most normal people, or they'll just name it HTC One 2013, which while not ideal, I think it would be a much better choice.
We can expect the device to have a 1080p screen, between 4.7" (if they keep the speakers on the front, which they probably will) and 5", 32 GB of storage by default, 3 GB of RAM, hopefully an 8MP "UltraPixels" camera with a 1/2"-2.3" sensor (whichever helps them get 2um pixels like before, at an 8MP resolution), and probably Qualcomm's next processor after the Snapdragon 800 (the one that will come with Adreno 400/420).
I do think that part is a little disappointing, though, especially since Samsung has basically hinted that the Galaxy S5 will have an ARMv8-based 64-bit CPU, and it will arrive only 2 months later. So the HTC M8 will be one of the very last flagships with an ARMv7 processor. This means HTC needs to push the M8 hard out of the gate, and take full advantage of that 2 months gap. They need to make sure a lot of people will hear about it, and think it's great, otherwise everyone might forget about it after new phones come out a few months later. This is probably not going to be easy for HTC, since they're losing money already, which means they probably won't have be able to do a lot advertising.
However the HTC M8 does, HTC will need to prepare another flagship for fall 2014, with an ARMv8 chip, because otherwise they'll lose even more money for the rest of the year, much like they did this year, since the One Max didn't do so well.