Okla. Admin. Code § 715:10-9-3
The designated beneficiary of an in-service member who qualified for service retirementand had ten (10) years or more of creditable service may elect to receive, in lieu of the return of contributions and the $18,000 death benefit, the retirement benefit to which the deceased member would have been entitled at the time of death under the Option 2 retirement plan. To qualify for this option, the designated beneficiary must have been named as the sole beneficiary at the time of the member's death (see OAC 715:10-15-1 and 10-15-2 and 70 O.S. §17-105(P)). This option is only available when the beneficiary is the member's spouse, another person, or the beneficiary of a Discretionary and Special Needs Trust, provided if the designated beneficiary is not the member's spouse, IRS Regulations require that the adjusted member/beneficiary age difference cannot be more than ten (10) years. [See OAC 715:10-15-10, to determine the adjusted member/beneficiary age difference]. [See also OAC 715:10-9-7, if the member and beneficiary were divorced before death].
Okla. Admin. Code § 715:10-9-3