Disney and NBCUniversal are locked in a dispute about how much the former must pay the latter for absorbing the rest of Hulu.

Disney late last year paid Comcast’s NBCU a previously agreed upon floor price of $8.6 billion and both sides had their own bankers calculating how much more, if any, was owed. Comcast had a put option on its Hulu stake, meaning it could force Disney to buy the stake. CEO Bob Iger might have been able to hand it off to someone else but decided to keep it and consolidate Hulu as part Disney’s streaming strategy.

But for how much? Not surprisingly, the former partners diverged. Disney’s camp figured it was in the clear, NBCU’s that another $5 billion was due. As provided for in the initial contract, the dispute was handed to a third party, a confidential arbitrator, for a final decision. In an...