AAA Corporate Yield vs 10Y Treasury

FRED's AAA10Y daily series runs from January 1983 onward, giving a 43-year window across four full credit cycles (1989-1991, 2000-2002, 2008-2009, 2020). The series median is 102 basis points, the mean is 109 basis points, and 60 percent of daily readings sit between 70 and 130 bps. AAA is Moody's highest corporate credit rating, awarded to issuers with the lowest probability of default in their statistical models, so the spread captures default premium and liquidity premium more cleanly than BAA-10Y does. The AAA universe has shrunk dramatically: in 1983 there were over 60 US non-financial AAA issuers; by April 2026 only Microsoft and Johnson & Johnson hold AAA ratings from Moody's (S&P AAA list is similarly thin: Microsoft, Johnson & Johnson). The shrinking universe is itself a structural input to the spread, because the seasoned BAA index captures a broader base of corporate borrowers while seasoned AAA increasingly approximates the spread for the highest-quality global credit. The Fed's Treasury Borrowing Advisory Committee (TBAC) and the BIS Quarterly Review both reference AAA-10Y as the cleanest US investment-grade default-risk indicator, and the April 2026 reading of 95 bps places it in the 35th percentile, in the lower-middle of the distribution. The percentile classification matters more than the absolute level because of the structural shifts that have repriced the post-2014 era versus the pre-2008 baseline, and reading the spread without normalising to its post-2014 distribution will systematically misclassify the credit regime.

The December 2008 peak at 372 basis points is the modern series high. The October 2002 peak hit 211 basis points during the corporate-fraud cycle. The March 23, 2020 COVID peak reached 277 basis points before the Fed's PMCCF and SMCCF announcement compressed the spread by approximately 100 bps within a week. Each episode produced an asymmetric move: the AAA leg widened by 80-120 bps while the 10-year fell by 100-150 bps on flight-to-quality, producing the upper-tail spread readings. The structural break in the series occurred between 2008 and 2014: pre-2008 average AAA-10Y was 88 bps, post-2014 average is 116 bps. The 28 bp lift reflects three structural shifts: (1) the shrinking AAA universe pushed the seasoned AAA index toward longer-duration issuers, raising the average yield; (2) post-Dodd-Frank dealer balance-sheet constraints widened the bid-ask premium structurally; (3) the post-QE term-premium compression suppressed 10-year yields by an estimated 50-80 bps, mechanically lifting the spread. Reading post-2014 spreads against pre-2008 baselines therefore overstates the credit-risk component. The 1989-1991 S&L crisis pushed AAA-10Y to 184 bps in October 1990, the highest pre-2002 reading, and the 1998 LTCM episode produced a brief 145 bp spike before the Fed's October 15, 1998 emergency 25 bp cut compressed the spread within four trading days. Each historical peak is dated to within days of the central-bank policy response that compressed it, which is a feature of the AAA leg's shorter reaction time versus longer-rated credit.