26 CFR §1.431(c)(6)-1

1. (a)Mortality tables used to determine current liability. In accordance with section 431(c)(6)(D), the mortality assumptions that apply to a single-employer defined benefit plan for the plan year pursuant to section 430(h)(3)(A) and (D) and §§ 1.430(h)(3)-1(a)(1) and (a)(2)(ii) are used to determine a multiemployer plan's current liability for purposes of applying the rules of section 431(c)(6). For purposes of this paragraph (a), either the generational mortality tables used pursuant to § 1.430(h)(3)-1(b) or the static mortality tables used pursuant to § 1.430(h)(3)-1(c) are permitted to be used without regard to whether the plan is a small plan. However, substitute mortality tables under §§ 1.430(h)(3)-1(a)(2)(i) and 1.430(h)(3)-2 are not permitted to be used for purposes of this paragraph (a).
2. (b)Applicability date. This section applies for valuation dates occurring on or after January 1, 2024.