If an app is still built using the watchOS 1 SDK (that came out alongside the original Apple Watch) and is opened on the watchOS 4.3.1 beta it displays a message that says, "The developer of this app needs to update it to improve its compatibility".
If you tap OK, it will still run the app though, which suggests Apple won't drop support when the official watchOS 4.3.1 upgrade rolls out. Instead many are speculating the upcoming watchOS 5 will sound the death knell for those apps built using the oldest SDK for the watch.
Instagram recently dropped its Apple Watch app and it's thought the company did this as it's based on the watchOS 1 SDK and it didn't see enough benefit in upgrading it with the more recent SDK tools.
We've also seen eBay, Twitter and Slack drop Apple Watch support over the last 12 months.
More big names?
Apple is encouraging developers to use the more recent watchOS 4 SDK, which makes sense as it's more stable and feature-filled than the original SDK released back in 2015.
If other developers don't see enough benefit in upgrading their apps to the new SDK, like Instagram, it likely means you won't be able to use them after upgrading to watchOS 5.
We don't know for certain that it'll be the end of the apps, but the evidence currently points toward that upgrade being the end point for these apps.
It's difficult to find whether popular apps are based on the older SDK without knowledge the each individual's development process, so we don't currently know what apps won't be available.
Considering every third-party app running on the original Apple Watch was based on watchOS 1's SDK, it may also be the company decides not to upgrade that watch to watchOS 5 software.
You can upgrade the original Apple Watch to watchOS 4, so it may still hold on for this update but we won't know for certain until we hear more details about the upcoming upgrade.
We expect to hear about that at WWDC 2018 which runs from June 4 until 8.
- All of the best Apple Watch apps
Via Apple Insider