Okla. Stat. tit. 60, § 175.86

A. A distribution interest in a trust shall be classified as a mandatory interest, a support interest or a discretionary interest. B. A beneficiary may concurrently hold a mandatory interest, support interest or discretionary interest. To the extent a trust contains a combination of a discretionary interest, a support interest or a mandatory interest, the trust shall be a mandatory interest only to the extent of the mandatory language and a support interest only to the extent of the support language. The remaining trust property shall be held as a discretionary interest.