Cal. Rev. & Tax. Code § 13534

In the case of any decedent dying on or after January 1, 1999, Section 6166 of the Internal Revenue Code, enacted as of January 1, 1998, shall apply to any tax due, and the interest rate on amounts due, as provided in Section 6601(j) of the Internal Revenue Code, enacted as of January 1, 1998, shall apply in lieu of the rate provided in Section 13550.