Fitch Ratings just released its finalized criteria for analyzing loans securing non-agency residential mortgage-backed securities under the qualified mortgage standard and ability-to-repay rule. Fitch said it will require more credit enhancement to loans that do not benefit from the QM safe harbor protection. Second, credit enhancement will be based on pool probability of default, which projects the maximum number of borrower challenges, as Fitch expects borrowers will only make a claim that the lender violated the rule as a defense to foreclosure.