API
Authentication is what differs. API tokens and Bearer authentication are available from FOG 1.6.0; on 1.5.x you authenticate with the token pair or HTTP Basic instead. Both older methods keep working on 1.6 and are not deprecated, so nothing you have already built needs to change.
Which version am I on?
Check FOG Configuration → FOG Settings → General → FOG_VERSION in the web UI, or the version string printed at the top of
installfog.sh.