Ignore fields you don't use. Treat new fields in responses as additive — adding a field is not a breaking change, and your client should not crash on unknown keys.
Pin to a specific API version in your client (the version selector on each reference page tells you what's current). Plan a migration window when a version is announced for deprecation rather than waiting until sunset.
Keep an eye on the Announcements page. Releases, breaking changes, and deprecations are published there with explicit dates — that's the canonical source for what's changing.