Put simply, the XM2w 4K is a wireless XM2 8K, minus the 8000 Hz. When looking inside, the two could be mistaken for each other: from the components to the shell design, the similarities are found everywhere. That is hardly a bad thing, however, given how the XM2 8K managed to impress with its buttons, build quality, and performance. Accordingly, it comes as no surprise that the 10 g over the XM2 8K mostly come from the 335 mAh battery on the XM2w 4K. At 61 g, the XM2w 4K can't quite keep up with the larger Razer Viper V3 Pro at 54 g or the likewise larger ASUS ROG Harpe Ace Aim Lab Edition also at 54 g, and merely matches the budget XM2we in this regard. On the flip side, build quality on my sample at least is a great spot: there is no rattle when shaking the mouse, no creaking or flexing of the shell when applying lateral pressure, and actuating the side buttons by pressing below them is impossible regardless of force applied. No changes have been made to the feet as well: still made of pure PTFE, these glide very well, and a set of replacement feet is included in the box, which doubles as a carrying case. Lastly, the coating is also still the same, providing great grip while also acting as a magnet for fingerprints.

As far as buttons go, the XM2w 4K is no different from the XM2 8K. For the main buttons, Kailh GX switches are still used. Being so-called SPDT switches, these have an additional top contact alongside the regular bottom contact, which can be used for various things. One possible use is to employ this contact as an additional layer of hardware debouncing, in that a click will only be registered if the bottom contact is closed and the top contact not closed. Another and arguably the more thrilling use case is the so-called GX Speed mode, by virtue of which a click will be registered already when the top contact is no longer closed instead of waiting for the bottom contact to close, reducing physical latency in the process. In my testing, enabling GX Speed Mode reduces click latency by 1.45 ms compared to non-Speed modes, which is a highly substantial reduction. In terms of feel, the GX switches are also great. Actuation is very firm and snappy, although also on the stiffer side, despite the actuation force rating of 55-60 gf. The button design likewise is sound, as lateral movement is minimal even when provoked, pre-travel is moderate, and post-travel low. For the side buttons, another set of switches from Kailh is used, although these are GM 2.0, which are proper full-size mechanical switches, unlike the low-profile and surface-mounted switches that have become ubiquitous on lighter mice lately. In any case, pre and post-travel are low, albeit a bit higher on the back button, actuation is even, and button response pleasing. For the scroll wheel, a TTC Silver encoder sees use, though this time around, the encoder has been hooked to the top shell. Either way, it impresses with very nicely defined steps, allowing for controlled scrolling, even though noise levels are elevated.

In terms of performance, the XM2w 4K ranks among the very best. Positive CPI deviation of 3.8% is present, but this is easily accounted for. General tracking shows no issues across the board, regardless of whether MotionSync is enabled or not. Of note is that unlike most other wireless mice, the XM2w 4K has its sensor run mode set to corded at all times, thus maximizing all sensor parameters and subsequently performance. Accordingly, the XM2w 4K does exceptionally well in terms of motion delay, as relative to the Logitech G403 (control subject), the XM2w 4K comes out ahead by 1.0 ms without MotionSync, which is on par with the likes of Finalmouse (UltralightX), G-Wolves (Hati-R 8K), or CHERRY XTRFY (M64/M68 Pro). Much like on the XM2 8K, polling rate has no effect on motion delay, which is why the lack of an 8000 Hz option is hardly meaningful, given that in order to ensure no missed polls, a larger buffer likely would have to be used, consequently resulting in worse latency compared to lower polling rates. Latency being unaffected by polling rate applies to click latency, too. In wireless operation, the XM2w 4K averages no more than 0.4 ms, which too is in striking distance of the aforementioned competitors. Latency aside, the XM2w 4K also has a well-implemented slam-click prevention algorithm, as no latency is added to the next click after lift-off, and there are no issues with idle delay or similar things, either. And of course, the 0.4 ms only applies to firmware-level latency—by enabling GX Speed Mode, physical click latency can be reduced by another 1.45 ms, putting the XM2w 4K far ahead of any mouse that isn't the XM2 8K or OP1 8K. Lastly, the target interval for each polling rate is exactly met throughout, and polling is stable, though I've noticed occasional bouts of elevated noise. That said, since no polls are actually being missed, I consider this negligible.

The stellar performance does come with a caveat, however, which is battery life. At 4000 Hz, Endgame Gear cites up to 30 hours, and even though the battery charge indicator found in the software is rather crude, I've been able to roughly corroborate this number. Compared to a competitor such as the Viper V3 Pro, which does 40 hours at 4000 Hz on a 306 mAh battery, this is still perfectly fine, but the issue is that the XM2w 4K doesn't provide many options to extend battery life much further. At 1000 Hz, battery life will be higher, but given that the sensor run mode will still be set to corded, I wouldn't expect much more than 40 hours. Compared to other wireless mice also using a PAW3395, the situation therefore is essentially reversed: typically, the sensor run mode is set to LP (low power) or HP (high performance) by default, and for those seeking every last ounce of performance, a "competitive" or "esports" mode can be enabled to set the sensor run mode to corded. On the XM2w 4K, on the other hand, corded is already the default, but there is no option to set it to something that isn't corded for those valuing battery life over small performance gains. As much as I sympathize with Endgame Gear's quest for the highest possible performance, I also believe that having options is always worthwhile, and it definitely wouldn't hurt to include a "high endurance" mode for 1000 Hz at least, to allow the XM2w 4K to creep towards the three-digit battery life numbers offered by the likes of Viper V3 Pro or Pro X Superlight 2.

Be that as it may, charging at least is notably speedy on the XM2w 4K, and the charging cable is plenty flexible, so the wireless experience on the XM2w 4K is a most pleasant one. The same can be said of the software, which still only takes up a miniscule 2 MB of RAM, reminding one of times when applications were written in Assembly, has all relevant options, and does not require installation. Even though web drivers have become increasingly popular lately, I still consider a self-contained app not requiring installation the most ideal solution, as it'll continue to function even when many of today's web drivers are no longer being hosted.

Overall, the XM2w 4K is yet another first-rate release from Endgame Gear, and the only area where it may indeed fall short of expectations is battery life, for those who simply don't care about higher polling rates, but don't want the XM2we for other reasons, either. At $129.99, the XM2w 4K is also quite reasonably priced, as it retails for less than direct competitors such as the Razer Viper V3 Pro ($159.99), Logitech G Pro X Superlight 2 ($159.00), ASUS ROG Harpe Ace Aim Lab Edition ($149.99), or VAXEE XE-S Wireless ($139.99). In my opinion, the $50 premium over the XM2we is also money well spent, as the XM2w 4K simply pulverizes its budget brother in terms of performance, while having far nicer switches to boot. As such, the XM2w 4K earns our Recommended award.