There are a litany of other mathematical and ML models that can more aptly be applied to the space.
But to answer your question more directly, yeah...there's no way in hell you'd let the questions your traders are asking in research out of the four walls of your building if you can avoid it.
Well, sure, but if the tokens aren't benefiting them enough to justify the cost it could make sense to do for cost reasons.
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.
Cost isn't the issue here.
1) Claude Code is only being taken away from traders.
2) Only traders have permission to send orders to the market and book client trades.
3) Claude code would have been running as the trader, under their account with minimal review.
If you run a coding agent in that environment it's only a matter of time until it enters a bad order or books a bad trade, and once that happens it's only a matter of time before management decides to take this kind of action.
Goldman is definitely not doing this for cost reasons. They can afford the tokens.