J P M O R G A N Global Securitized Products Research 14 July 2026 TBA Definition Update Wednesday, July 15 In this update, we modestly adjust the definitions for coupons in UMBS 30s, UMBS 15s, and G2s to keep them in line with the likely deliverable. The impact to OAS is flat to tighter. These definitions will go into effect on Wednesday, July 15, and valuation changes will appear in the packet produced for the morning of Thursday, July 16. Figure 1: A quick look at the Tsy OAS impact of the update Tsy OAS ...