The API IP-restriction is tied to the System Admin IP restrictions. (At least as I understand it.) Adding IP restrictions for a system admin also applies those IP restrictions to any API call requiring sys admin credentials. 

This is nice to know considering we just setup a specific account that only our own servers will use, and had applied IP restrictions to the account - not knowing that the API didn't apply IP restrictions that were defined on an account up until this build. That must be what makes this release critical.