It does not need an exception. The thing about the filibuster rules is that they are only rules if the members of the Senate agree that they are. At any point t

It does not need an exception. The thing about the filibuster rules is that they are only rules if the members of the Senate agree that they are. At any point they can change the rules, and can even just decide that a particular piece of legislation or legislative activity is so important that it can bypass the rules. A multi-national agreement that raises corporate tax rates on US companies operating outside the US is pure win for the party currently in control of both the legislative and executive branch; it plays well with the electorate, it is easy to weaponize against your opponents, and the actual impact to the companies caught up in the changes will not be as unpleasant as they may claim in public.