Ackman, the CEO and Portfolio Manager of Pershing Square Capital Management, made this announcement on X, the platform formerly known as Twitter, stating that the economy is slowing down faster than recent data suggests.

This decision by Ackman has had a significant impact on bond markets, with yields on 30-year Treasuries falling about 5 basis points to 5.03% on Monday. Earlier, they had surged as much as 10 basis points to about 5.18%, the highest level since 2007, compared to around 4% at the end of July. Ackman's three tweets expressing his concerns about global risk turned the bond markets in an opposite direction.

Bill Ackman, known for his investment expertise, co-founded Gotham Partners Management Co., LLC, before starting Pershing Square Capital Management. Ackman has a strong investment philosophy based on concentrated research-intensive fundamental value investing in long and occasionally short positions in public markets. He is a prominent figure in the financial industry, serving as Chairman of The Howard Hughes Corporation and a member of the board of Universal Music Group N.V. Ackman's knowledge and experience earned him a position in the Investor Advisory Committee on Financial Markets for the Federal Reserve Bank of New York.

In early August, Ackman disclosed that he had taken a bearish stance on long-term Treasuries via options as a hedge for his equity investments. He cited structural changes such as deglobalization and the energy transition as factors that could fuel inflation pressures in the long term. Ackman also mentioned that the increasing bond supply to fund expanding US budget deficits could lead to higher yields.

However, on Monday, Ackman revealed his change in sentiment, disclosing that he had covered his previous bets against Treasuries. The billionaire investor expects that the ongoing global risk, including geopolitical tensions, will push more investor dollars towards US Treasuries.

Currently, the yield on the two-year Treasury note stands at 5.06%, while the yield curve between the two-year and 10-year Treasury is the steepest it has been since mid-July, standing at minus 22.7. The Treasury Department recently auctioned $75 billion in 13-week bills and $68 billion in 26-week bills. Throughout this week, the market awaits further supply with a $51 billion auction of 2-year notes on Tuesday, $52 billion in 5-year notes on Wednesday, and $38 billion in 7-year notes on Thursday.

Bill Ackman's decision to cover his short bet on US Treasuries highlights the increasing concerns surrounding global risk. The impact on bond markets and the shift in Ackman's approach will undoubtedly make investors reassess their strategies in the current economic landscape.