Glossary term
Option-Adjusted Spread (OAS)
The extra yield a corporate bond pays over Treasuries after removing the value of any embedded call or put option, so bonds with different structures can be compared. Index-level OAS for investment grade and high yield is the standard gauge of credit conditions.
AI-generated — produced automatically by Closelook’s systems under this site’s editorial policy.
What it means
A corporate bond yields more than a Treasury of the same maturity because it can default and because it is less liquid. The plain difference is the credit spread; the option-adjusted spread strips out the part of the yield that compensates for an embedded option — most corporate bonds can be called by the issuer — so that a callable and a non-callable bond can be compared on the same footing. It is quoted in basis points.
The two index series everyone watches are the ICE BofA US Corporate index (investment grade) and the US High Yield index. When they widen, lenders are demanding more for risk; when they sit near multi-year lows, credit is loose regardless of what interest rates are doing.
Why it matters for the AI trade
OAS answers the question that yield alone cannot: did an AI borrower’s bond fall because Treasuries fell or because lenders doubt the borrower? On 11 September 2026 investment-grade OAS was 0.80% and high-yield 2.65% — the fourth percentile of three years — while the ten-year Treasury touched 5%. Oracle’s 2055 bond yielded 7.62%, but the spread over Treasuries had barely moved; the move was rates, not credit.
A widening of index OAS with AI issuers widening more than the index is the credit event the AI credit stress tape is built to catch — and had not caught as of September 2026.
How Closelook uses it
The credit stress tape decomposes each issuer’s yield change into the Treasury move, the index OAS move, the rating-cohort move and an AI residual; the environment panel shows IG, BBB, single-B and high-yield OAS with their three-year percentiles. The broader credit spread entry covers the concept without the option adjustment; high yield versus investment grade explains the rating line.
Common questions
- What is a normal OAS for investment-grade bonds?
- Roughly 0.8% to 1.5% over Treasuries in calm markets; it rose above 3% in the 2020 shock and above 6% in 2008. A reading near 0.8%, as in September 2026, is tight by any historical measure.
- Why not just use the yield difference?
- Because most corporate bonds can be called early by the issuer, and that option is worth something to the issuer and costs the investor. Removing it makes bonds with different call schedules comparable and makes the index series consistent over time.
- Does a tight OAS mean AI debt is safe?
- It means the market is not charging for credit risk right now. Our tape treats tight spreads as the reason to watch the issuer-specific residual rather than the level: stress that starts in one AI borrower shows there long before the index moves.