Honestly, for a 14-hour trek to Tokyo, you really want the best noise canceling possible. I have spent hundreds of hours in the air with both and the Sony WH-1000XM5 Wireless Noise Canceling Headphones are an absolute game changer! While the Sony WH-1000XM4 Wireless Noise Canceling Headphones are definitely easier to pack since they fold down, the XM5 is just leagues ahead when it comes to high-frequency noise isolation. If youre trying to sleep, the XM5 feels much lighter on the head during those long stretches. The auto-optimizing ANC handles cabin pressure changes way better than the older model too. Even tho the case is slightly bigger, I usually just slide it into the laptop sleeve of my carry-on. You definitely wont regret the extra silence once those engines start roaring! Its worth the bulk for the peace and quiet alone.

Re: "Totally agree about the XM5 being top-tier, but..." - honestly, if your carry-on is already bursting at the seams, you might want to consider the Sony WF-1000XM5 Noise Canceling Earbuds instead. I did a 13-hour haul to Narita last year and brought my big over-ears, but man, trying to sleep against the window was a total nightmare with those bulky cups. My neck was killing me by hour eight because I just couldnt find a comfortable spot for my head with the headband in the way. I would suggest being careful with earbuds for that long tho, cause ear fatigue is real. Make sure to test the different foam tips before you leave. The noise canceling on these is actually wild for something so small, and theyll save you a ton of space compared to the XM4 or XM5. Plus, they're usually a bit cheaper which helps with the budget. Just don't forget to charge the case during the flight... nothing worse than silence dying halfway over the Pacific.

^ This. Also, if you are worried about reliability and space, there are a couple of other Sony options that still work great for travel.

• Sony WH-1000XM3 Wireless Noise Canceling Headphones: I still use these for my long hauls. The build feels a bit sturdier than the XM5 and they fold up small like the XM4. Noise canceling is nearly as good as the newest ones, and they are basically indestructible. No issues after years of being tossed in bags.
• Sony WH-XB910N EXTRA BASS Noise Canceling Headphones: These are a decent alternative. They fold up properly for tight bags and the battery life is solid. Noise canceling isnt as top-tier as the flagship line but for low frequency engine drone, it gets the job done fine. If your carry-on is really that tight, the folding hinge on these is more reliable for travel than the fixed arm on the XM5. The newer model looks nice but it takes up way too much room in a bag... basically depends on how much you value that extra inch of space.

Totally agree about the XM5 being top-tier, but if youre trying to save some cash for sushi in Tokyo, check out the Sony WH-CH720N Noise Canceling Wireless Headphones. I've been super satisfied with mine lately. Theyre crazy lightweight and actually use the same V1 processor as the XM5. You get solid noise canceling for way less money, and the battery easily lasts that 14-hour trek.