Update: Niantic has backed away from this and announced that they are deferring this decision after all.
Niantic, the company behind Pokémon GO, announced recently that Pokemon GO will no longer work on 32 bit Android devices from August. You'd be forgiven for having missed this, as although it's on the official blog, it doesn't show in the in-game news.
Whilst the announcement makes it sound like only older devices will be affected, this is not the case. Many newer Android phones ship with 64 bit hardware, but a 32 bit operating system, in which case they are, for all practical purposes, 32 bit devices and are restricted to running 32 bit apps.
Unless a device has more than 4GB of RAM, there's not any great advantage to using a 64 bit OS, so a lot of budget phones come with a 32 bit operating system. For example, a large number of devices in the Motorola G range and the Samsung A and J ranges have only a 32 bit OS, even some of those released in the last 12 months. The Silph Road community on Reddit has started to assemble a list of modern devices that will be affected by this change.
Unfortunately, it's not clear that Niantic has understood the distinction between the architecture of the CPU and the architecture of the operating system. The devices in their list of examples all have 32 bit CPUs. It is very possible that they have made this decision based on data collected on hardware, and have not looked at operating system architecture data. I suspect the fact they've given this quite a low-profile announcement means they have estimated that this will not affect many people, and I also suspect that it will actually affect a large number of people. This seems like the kind of announcement that should be made 12 months in advance, not 6 weeks.
For those who will be affected by this, I recommend waiting until closer to August before replacing your device. Niantic may have made a mistake and may yet back down.
It's also worth noting that it's actually quite difficult to determine if you're buying a 32 bit or 64 bit device, as a lot of manufacturers don't publish this information. If you do need to replace your device, choose carefully.