That BAX and MNTA are now working on the third FoB in the collaboration presumably means that BAX has exercised the option to develop compounds #3-#6, which results in a $28M milestone payment to MNTA—see #msg-70258421.
Prediction: The first 3 FoB’s in the BAX-MNTA collaboration are Humira, Orencia, and Erbitux. (Craig Wheeler’s hint on today’s CC is consistent with this prediction.)