Apple also announced that starting on April 1, 2018, updates to watchOS 1 apps will no longer be accepted. All updates must be native apps built with the watchOS 2 SDK or later. Newly submitted watchOS apps should be built with the watchOS 4 SDK or later.
Apple first began requiring new apps to use the watchOS 2 SDK in June of 2016, and now that will also apply to app updates that are submitted. watchOS 1 apps that are not rebuilt using watchOS 2 SDKs or later will no longer be able to be updated after the April 2018 deadline.
Apps built with the native support features that were first introduced in watchOS 2 are able to run more quickly and operate more smoothly on the Apple Watch.