Okla. Stat. tit. 12 § 1
The Oklahoma Pleading Code governs all proceedings in actions pending on the day that it takes effect, except to the extent in the opinion of the court its application in a particular action would not be feasible or would work injustice, in which event the former procedure applies. Pleadings, motions and other instruments that were filed prior to the effective date of the Code and that were sufficient at the time they were filed shall continue to be effective after the Code takes effect, and if at the time the Code takes effect a party is required to file or serve a pleading or motion to take other action, the time to take such action shall not be shortened by any provision of the Code, Although an action is commenced before the effective date of the Code, Section 2011 in regard to the signing of pleadings and motions shall apply to all pleadings and motions that are served or filed on or after the effective date of the Code, and Section 2013A in regard to compulsory counterclaims shall apply to all answers, answers to cross-claims, answers to third-party claims and answers to claims asserted by plaintiffs against third-party defendants that are served or filed on or after the effective date of the Code.
Okla. Stat. tit. 12, § 1