Aside from the price (the XM4 are $50 cheaper), the differences mostly come down to the max battery life, noise cancellation capabilities, and design. The XM5 are noticeably slimmer than previous generations, with a clean, minimalist look and super-soft, faux leather headband. They also contain eight built-in microphones for active noise cancellation, an increase from the five found in the XM4.
Lastly, the XM5 have a max battery life of 40 hours, a jump from the XM4's max of 30 hours — although it's worth noting that the XM5 can only last that long when ANC is turned off and power-saving audio settings are selected.
If you're not willing to fork out that much money on the XM5 headphones, then check out the latest prices for the still-excellent XM4 below. We expect prices to start dropping even more once the new model starts to take over.