The Treasury basis trade and March 2020

A trade too dull to explain

The cash-futures basis trade buys a Treasury bond, sells a Treasury futures contract against it, and pockets a spread of a few tens of basis points. Hedge funds run this every day. In the years running up to 2020, it grew enormously: hedge funds' total Treasury exposure rose by almost $1 trillion between 2017 and 2019 alone, as the arbitrage became more attractive and more crowded.

On the surface the trade looks close to riskless. A long position in the bond's price risk and a short position in the future's price risk mean that a rise or fall in interest rates affects both legs in opposite, roughly offsetting ways. What is left over, the basis, is a thin, usually stable gap between the cost of carrying the bond and what the futures market pays for that exposure. The whole business model, though, only works at very high leverage, financed almost entirely through overnight repo borrowing. A few tens of basis points is not an attractive return on its own; it becomes one only once magnified many times over on a small sliver of investor equity.

A safe haven that stops acting safe

By early 2020, this crowded, highly leveraged position sat quietly in the background of the Treasury market, the deepest and supposedly safest government bond market in the world. Then Covid-19 hit. In the last days of February and first days of March, investors rushed into Treasuries as a safe haven, driving the 10-year yield down to about 0.54% on 9 March, a historic low. Within days, the crisis turned into something else: a broad dash for cash. Funds needed dollars everywhere at once, for margin calls, for redemptions, for anything that could be turned into liquidity fast. Basis trades, financed in repo and marked to market daily on the futures leg, were an obvious place to raise cash from, so funds began unwinding them, selling the cash bonds and buying back the futures.

That selling landed directly on the asset everyone had just fled into for safety. Between 9 and 18 March, the 10-year Treasury yield reversed sharply, rising from about 0.54% to about 1.18%, a move of 64 basis points in just nine days, the opposite direction from what a simple flight-to-safety story would predict. Bid-ask spreads widened, repo rates on Treasury collateral spiked, and the basis itself, normally a sleepy few basis points, blew out. The safe asset had briefly stopped acting safe.

The Fed as buyer of last resort

The Federal Reserve responded at a scale that matched the shock. On 12 and 13 March, the New York Fed sharply increased its repo operations to ease funding strains. On 15 March, the Fed cut its policy rate to 0-0.25% and pledged to buy "at least $500 billion" of Treasuries. On 23 March, it went further still and made its purchases open-ended, promising to buy Treasury and agency mortgage-backed securities "in the amounts needed to support smooth market functioning." Purchases peaked at about $75 billion a day between 19 March and 1 April, and by the end of the quarter the Fed had bought more than $1 trillion of Treasuries in total, the fastest balance-sheet expansion in its history to that point. The market stabilised. Hedge funds, for their part, had by then sold more than $200 billion of cash Treasuries and cut their total Treasury exposure by about $430 billion.

The trade survives, the rules change

The episode did not end the trade. By May 2025, leveraged funds' short Treasury-futures notional, a broad proxy across the 2-, 5- and 10-year contracts, had grown back to more than $1 trillion. What changed was regulation. In December 2023, the US Securities and Exchange Commission adopted a rule requiring central clearing for large parts of the Treasury cash and repo markets, a direct response to episodes like this one. Compliance dates, after a further extension in February 2025, run to the end of 2026 for cash Treasury transactions and mid-2027 for repo.

The case therefore turns on a single distinction. The trade never stopped being duration-neutral. It was never funding-neutral, and funding is what broke.

Three legs, one thin spread

The trade has three legs. Leg 1: buy the cheapest-to-deliver Treasury bond. Leg 2: sell the matching Treasury futures contract short. Leg 3: finance the bond purchase in the repo market, rolling the funding over short intervals, often overnight. Netting legs 1 and 2 together leaves not a bet on the level of interest rates, but the basis, the net cost of carry. That is coupon income earned while holding the bond, minus the financing cost of carrying it, minus or plus the futures contract's own richness or cheapness relative to fair value. The basis is normally only a few tens of basis points, and it converges towards zero as the contract approaches delivery.

Because the basis is thin, the trade is only worthwhile at high leverage. A large enough position, financed almost entirely in overnight repo against a very small sliver of investor equity, turns a few tens of basis points of basis into a double-digit annual return on that equity. This is the same leverage mechanism at work as with margin: a small move gets amplified into a large one on equity. Here, it is applied to the safest asset in the world.

Neutral on rates, exposed on funding

The structural fact that matters is that the trade is close to duration-neutral. Long the bond's duration, short the futures' duration, so the two largely cancel, which is why the position looks safe from the direction of interest rates. What it is not neutral to is funding. The bond is financed in repo that must be rolled, typically overnight, and the futures position is marked to market and margined every day. If either financing channel tightens, for example if repo rates spike or margin requirements rise in a broad market panic, the fund must find cash fast, or unwind. Unwinding means selling the cash bond and buying back the futures, in a hurry, in the same market that is already under stress. Margin turns credit risk into liquidity risk, and it does so even inside the market regarded as the ultimate safe haven.

Three building blocks, one shock

March 2020 is the proof. As Covid-19 fears spread, investors first rushed into Treasuries, pushing the 10-year yield to its low. Then, as the crisis widened into a dash for cash, funds needed dollars for margin calls and redemptions everywhere, including from their basis positions. Selling Treasuries to raise cash, and the unwind of basis-trade positions alongside it, contributed to the sharp yield reversal described above. The conversion factor and cheapest-to-deliver bond link the futures price to a specific cash bond; the basis is the net cost of carry applied to bonds instead of commodities; and margin turns funding stress into forced sales. None of these three ideas is new on its own. What March 2020 shows is what happens when all three combine at trillion-dollar scale, financed overnight, in a single market shock.