A complicated decision by the Federal Circuit gives us all an opportunity to review the MedImmune standard. Prior to MedImmune a licensed party could not bring an invalidity suit because it need not fear infringement (i.e., no case or controversy). MedImmune loosened that standard and essentially set forth a “look at all the circumstances” test.
So what if a party kinda asserts patent claims, but it’s really not clear, and then later gives a covenant not to sue. Somewhat predictably the “all the circumstances” test leads to a 2-1 split in ArcelorMittal v. AK Steel. The panel ends up disagreeing on whether the circumstances of a “covenant not to sue” moot the underlying controversy.
Aaaaaand… that’s really all you need to know unless you want the complicated details of this case.