Technically yes, but in practice:

a) They are pulling it entirely rather than imposing a cap or enforcing the use of cheaper models. This would be a strange choice if cost was the only concern.

b) Famously, traders at Goldman are well renumerated. Given the costs of these people even small productivity improvements carry a large value.

c) It would be very difficult to determine in any kind of conclusive way that the benefits were smaller than the costs.

For all these reasons I find it totally implausible that this decision was driven by API costs.

Having sat in a trading seat at a GS competitor, I can second this. If a Claude Max subscription led to one better trade over the course of a year, there's an almost 100% chance that it would pay for itself. And consider that a trader at GS would be doing dozens if not thousands of trades per day (depending on the seat/product).

Cost isn't the issue here.