Complicated naming aside, the 1000X line has produced class-leading cans in recent years, and the XM4s look just as formidable. Here's everything you need to know.
When will the Sony WH-1000XM4 be released?
As was widely expected, Sony unveiled the XM4 headphones at its online-only event on 6 August.
How much will the Sony WH-1000XM4 cost?
The XM4 are priced identically to 2018's Sony WH-1000XM3, so will set you back £350/US$349.99/AU$549.
That might sound like a lot, but they're priced roughly in line with other flagship headphones on the market. The XM3 also earned a rare five-star review, so you're willing to pay a bit more when you get this sort of quality.
Sony WH-1000XM4 new features
Sony's latest flagship headphones extensively leaked ahead of the official announcement, and many of these made their way into the final product.
It's clear that Sony is focusing on internals with the XM4, as the design is largely unchanged from the previous generation. However, with many people praising those cans' look and feel, it perhaps made sense to stick with a winning formula.
The only differences here come in the form of a slightly more snug fit and slight reduction in overall weight, both modifications that consumers should be a fan of.
Onto the more significant improvements then, starting with noise cancelling. It might seem like the class-leading noise cancellation we saw on the XM3 couldn't get any better, but Sony is attempting to stretch its lead over rivals.
The XM4 comes touting Sony's 'best ever noise cancelling performance', complete with built-in microphones which will supposedly capture external sound and apply noise cancellation in real-time, with the help of Sony's built-in Q1 processor.
Sony has retained the Adaptive Sound Control feature from the XM3, which will learn from situations you regularly use the headphones in and adjust the sound accordingly. This should allow you to focus on the audio while on the train, but not block out all sound if you need to concentrate while crossing the road.
Speak-to-chat is arguably the most impressive new feature, which automatically pauses music if it recognises you talking. It will also recognise your own voice to know when to stop the audio, automatically resuming if it hasn't heard anything for 30 seconds.
However, some people have reported that they paused the music when detecting singing, which we'll have to test for ourselves.
As is the case with many modern headphones, the XM4 are also able to detect when you've taken them off and pause your music. Audio resumes once you put them on again.
Sony has also said the XM4 headphones will be able to detect when you're speaking to someone in person, as opposed to chatting on a voice call.
There's also a new multipoint connection feature, which means you can be connected to two devices at the same time without impacting on sound quality. This avoids the potentially fiddly task of disconnecting from one device and reconnecting to the other.
That comes as part of the upgrade to Bluetooth 5.0, which also brings improved wireless range and more reliable connectivity.
Sony is also attempting to bridge the gap on sound quality to wired headphones, which typically offer more well-rounded audio. The company's Edge-AI technology is aiming to "rebuild audio lost during digital compression for a full-fidelity experience".
The XM4s retain Sony's 360 Spatial Audio feature, which should make it feel like the sound is coming at you from all angles.
In terms of battery life, Sony has said you'll be able to get an impressive 30 hours of battery life, even with noise cancellation turned on. That's exactly the same as the XM3, while quick charging via USB claims to get you five hours of battery life in just ten minutes.
Unfortunately, nothing was revealed with regards to call quality, so we'll have to see if there are any improvements when we test them for ourselves.
We scored the Sony WH-1000XM3 a rare five stars in our review so we're looking forward to trying out the enhancements on the XM4 for ourselves.