Investors are boosting their bullish bets on US equities, making positioning increasingly “one-sided,” according to Citigroup Inc. strategists.

Market participants have added $21 billion in new long positions on S&P 500 futures, Citi’s data showed, even as talks in Washington to resolve the debt-ceiling impasse drag on. The weekly flow of new longs was one of the largest seen in recent years, it added.

“The momentum is clear, and positioning is increasingly one-sided. Longs outnumber shorts by more than 9 to 1,” said Citi strategists led by Chris Montagu. “The few remaining shorts are all in loss, but a short squeeze is not likely to significantly impact markets.”

That echoed data from Goldman Sachs Group Inc.’s prime brokerage unit: Hedge funds that make both bullish and bearish equity wagers have snapped up US shares for two straight weeks, with total purchases reaching the fastest pace since October.

The turn in sentiment comes just as the S&P 500 Index has reached a closely watched breakout level of 4,200 points, which had capped further upside twice this year. US stocks have been sailing higher as robust earnings and bets on a rate-hike pause by the Federal Reserve have fueled appetite.

What’s more, volatility readings have also fallen to the calmest levels seen in over a year, despite potential risks such as the ongoing negotiations to avoid a catastrophic US default.

“We continue to think that equity markets are pricing in more good news than bad, and that macro uncertainty on the horizon means the recent rally looks vulnerable,” said UBS Global Wealth Management strategists led by Mark Haefele. They expect the US to reach a last-minute deal on the debt ceiling but say that markets will be volatile ahead of the compromise.

Notably, the recovery in US equities this year has been led by a few large tech stocks as investors shifted toward companies with strong earnings potential and away from cyclical industries. According to Goldman Sachs, US mega-cap tech shares topped popular hedge fund long positions in the first quarter.

The lack of breadth can become a risk to stocks should the momentum start to fade. Some technical indicators such as the relative strength index for the Nasdaq 100 Index are already flashing “sell.” For the rally to carry on, investors might want to see a broadening of risk taking.

S&P 500 and Nasdaq futures were little changed as of 7 a.m. in New York on Tuesday.