Launched last month (and currently available for pre-order), the Powerbeats Pro has recently been confirmed to offer a IPX4 rating in terms of its water-resistance. This information is not openly advertised by Apple or Beats, but according to publications that got their hands on the review units, it is stated in the marketing materials that they do have an IPX4 rating.
For those unfamiliar, devices that are water-resistant and dust-resistant usually come with an IP rating that lets users know how water or dust-resistant their gadgets are. In this case of the Powerbeats Pro and its IPX4 rating, it means, “Water splashing against the enclosure from any direction shall have no harmful effect.”
Basically it sounds like it should not have any issues with sweat or if you were to wipe it down with a damp cloth, but if you were to try rinsing it off under running water in the shower, or if you were to use it while swimming, there is a good chance you could damage it for good. Ideally an IP rating of IPX7 would be much more ideal, but for the most part, IPX4 should be good enough for most gym usage.