Constructing the SOFR Term Structure: A Trader's Guide to Curve and Butterfly Spreads

The Great Conversion: A Post-Mortem on the Eurodollar-to-SOFR Switch

On April 14, 2023, one of the most significant events in the history of financial engineering took place: the CME Group converted all outstanding eligible Eurodollar futures and options contracts into their Secured Overnight Financing Rate (SOFR) equivalents. This was the culmination of a multi-year effort to transition the global financial system away from the scandal-plagued LIBOR. For traders who held legacy Eurodollar positions, this was a moment of significant risk and opportunity. A post-mortem of this conversion offers valuable lessons in pricing, risk management, and the mechanics of market structure change.

The Mechanics of the Fallback

The core of the conversion was the application of a “fallback spread.” Since LIBOR (an unsecured, credit-sensitive rate) was historically higher than SOFR (a secured, risk-free rate), simply replacing one with the other would have resulted in a massive value transfer between parties. To prevent this, the International Swaps and Derivatives Association (ISDA) determined a fixed spread adjustment to be added to the SOFR rate to make it comparable to LIBOR. For 3-month USD LIBOR, this spread was calculated as the five-year historical median difference between the two rates, which was determined to be 26.161 basis points.

For Eurodollar futures, the conversion was straightforward. On the conversion date, each remaining Eurodollar futures contract was delisted and replaced by a SOFR futures contract for the same delivery month. The price of the new SOFR contract was derived from the final settlement price of the Eurodollar contract, adjusted by the fallback spread. Specifically, the price of the converted SOFR future was set to the Eurodollar future’s price plus 26.161 basis points (since futures are priced as 100 minus the rate).

For options on Eurodollar futures, the process was more complex. Each Eurodollar option was converted into a SOFR option with the same expiry date, but the strike price was adjusted. The new strike price for the SOFR option was set to be 26.161 basis points higher than the original Eurodollar option’s strike price. This ensured that an option that was, for example, at-the-money in Eurodollar terms would remain at-the-money in SOFR terms after the conversion.

Pricing and Risk in the Run-Up to Conversion

In the months and years leading up to the April 2023 conversion, the market was not idle. The impending conversion created a unique set of pricing and risk management challenges for holders of legacy Eurodollar positions.

• The Basis Trade: The most obvious trade was the convergence of the Eurodollar-SOFR basis towards the fixed fallback spread. Traders could put on a spread trade by selling a Eurodollar future and buying a SOFR future for the same expiry month. As the conversion date approached, the spread between these two contracts was mathematically guaranteed to converge to 26.161 basis points. Any deviation from this value in the market was a potential arbitrage opportunity. In the final months, this spread became a very low-risk, high-volume trade for arbitrage-focused firms.

• Option Skew and Volatility: The conversion had a significant impact on the volatility surface of Eurodollar options. As the conversion became a certainty, the uncertainty around the future of LIBOR vanished. This led to a collapse in the implied volatility of Eurodollar options, particularly for longer-dated expiries. Traders who were long volatility on Eurodollar contracts saw the value of their positions erode. Conversely, traders who correctly anticipated this volatility crush and sold Eurodollar options profited.

• Managing Legacy Positions: For institutions with large, complex portfolios of LIBOR-based derivatives, the run-up to the conversion was a important period for risk management. Many chose not to wait for the official conversion and instead proactively transitioned their positions. This involved closing out their LIBOR-based swaps and futures and re-establishing them in the more liquid SOFR market. This process, known as “pre-transitioning,” allowed them to manage their risk on their own terms and avoid any potential operational or pricing risks associated with the bulk conversion event.

A Post-Mortem: Lessons Learned

The successful conversion of trillions of dollars in notional value of Eurodollar contracts was a remarkable achievement for the financial industry. It demonstrated that a large-scale, complex transition in market structure is possible with careful planning and coordination. Several key lessons can be drawn:

1. The Power of a Clear Mandate: The clear and unwavering deadline set by regulators was important. It forced the market to take the transition seriously and invest the necessary resources to prepare.
2. The Importance of a Standardized Fallback: The ISDA fallback methodology, with its fixed spread, provided a clear and predictable outcome. This eliminated a huge amount of uncertainty and allowed the market to price the conversion accurately in advance.
3. The Efficiency of Market-Based Convergence: The market itself proved to be a highly efficient mechanism for managing the transition. The convergence of the Eurodollar-SOFR basis to the fallback spread was a textbook example of how arbitrageurs can enforce pricing relationships and facilitate a smooth transition.

For traders, the Eurodollar-to-SOFR conversion was a once-in-a-generation event. It was a masterclass in the pricing of derivatives, the management of basis risk, and the impact of market structure on trading opportunities. While the Eurodollar contract may be gone, the lessons learned from its demise will continue to inform the way traders approach risk and opportunity in the ever-evolving world of finance.