Reuters Credit Suisse Bondholders Enraged As $17B Of AT1 Debt To Be Written Down To Zero: What It Means Credit Suisse Group AG (NYSE: CS) said 16 billion Swiss francs ($17.24 billion) of its additional tier 1 (AT1) debt, a type of bond, will be written down to zero on the orders of the Swiss regulator FINMA as part of its rescue merger with UBS Group AG (NYSE: UBS). The decision by the Swiss regulator would mean AT1 bondholders may be left with nothing while shareholders, who sit below bonds in