After a rally through the first half of the summer, Wall Street bank stocks have lost their luster as rising interest rates threaten to cool their investment banking and trading booms that have powered their earnings.

Despite reporting sturdy third quarter results in early October, the signs of a slowdown in deals and trading activity have begun to pick up. The environment only raises the stakes for Anthropic's highly anticipated public debut, which could come as soon as Nov. 16.

Each of the five biggest Wall Street banks has won a mandate to help in Anthropic's planned November listing, according to the startup's S-1 filing. On average, the IPO could represent a roughly 0.8% boost to banks' fourth quarter earnings, according to Evercore calculations, which are based on their fees earned from SpaceX's June IPO. Goldman Sachs, Morgan Stanley, and Citigroup stand to see the biggest lifts.

All in all, Anthropic's IPO "could be the swing vote" in 2026's final quarter for these banking giants, Evercore's Glenn Schorr wrote to clients on Tuesday.

So far in the fourth quarter, investors have already shown some selectivity in Wall Street bank stocks. From the beginning of October through Nov. 2, JPMorgan's (JPM) stock is up 3%, while Goldman Sachs' (GS) stock is flat and Morgan Stanley's (MS) stock is down 1.2%, according to Yahoo Finance data. Shares of Citigroup (C) and Bank of America (BAC) are down 5% and 9%, respectively.

The KBW Nasdaq US bank index ( ^BKX ) is up more than 2% over the same period.

In October, worldwide investment banking activity fell 25% from a year earlier while US stock trading volumes tumbled 8%, according to Dealogic data cited by Evercore ISI.

A wider Federal Reserve survey released Monday found that US banks broadly tightened standards in the third quarter compared to the second quarter, reversing a four-quarter trend of easing standards amid fiercer competition. Borrowing demand also weakened across most loan categories.

What's adding even more uncertainty to the picture is Wall Street's growing skepticism of the AI investment boom, which has powered a wide swath of trading and dealmaking fees major banks have earned this year.