I'm integrating with CRM through PHP and I use the API URL https://example.com/XYZ/api/data/v8.0/ which works well.
My question is, will a future minor upgrade of CRM break this URL? E.g if it is upgraded to version 8.2, will /XYZ/api/data/v8.0/ stop working and I'll have to somehow automatically discover this by my PHP app which will from that point onwards need to use /XYZ/api/data/v8.2/?
When Microsoft publishes a new version of the API, they'll bump the version number, say api/data/v8.2, but the earlier versions will still persist. The whole point of versioning APIs is to be able to introduce new functionality without breaking old implementations of the API.
Eventually though, they might deprecate old versions of the API, but I suspect this will take a long time, and you'll probably get some kind of warning.
Here you can see the changelog of the SDK versions, and as you can see, none of the versions have been discontinued as of now.