Magnite promotes Gephart to CFO and Sullivan to CAO as Day retires

Magnite, Inc. (NASDAQ: MGNI) appointed Brian Gephart as chief financial officer and Haas Sullivan as chief accounting officer, both effective October 1, 2026, and said in a September 21 press release that Gephart succeeds retiring CFO David Day after a decade in the role.

Magnite disclosed a paired finance-leadership change: promoting its chief accounting officer into the CFO seat and elevating its vice president of accounting into the CAO role, both effective the same October 1, 2026 date.

Gephart to CFO effective October 1

In a Form 8-K under Item 5.02, Magnite said that on September 18, 2026 it appointed Brian Gephart, age 47, as Chief Financial Officer and principal financial officer, effective October 1, 2026. Gephart has been Magnite’s Chief Accounting Officer since June 2021. Before Magnite, he was CFO and principal financial officer of Leaf Group from May 2020 (and CAO/principal accounting officer from June 2019 to May 2020), CAO of JH Capital Group from August 2017 to April 2019, and a PricewaterhouseCoopers director in capital markets and accounting advisory from July 2011 to August 2017. He holds a bachelor’s degree in accounting from Hillsdale College, an M.B.A. from DePaul University, and is a CPA. The 8-K states he has no family relationship with Magnite directors or executive officers and no Item 404(a) related-party interest.

Equity award and amended severance for Gephart

In connection with the CFO appointment, Magnite said Gephart will receive an equity award with a total value of $2.25 million — 70% RSUs ($1,575,000) granted October 1, 2026 vesting over four years with a one-year cliff, and 30% PSUs ($675,000) expected to be granted with other executives’ 2027 annual PSU grants. Magnite also amended his Executive Severance and Vesting Acceleration Agreement: on an involuntary termination outside a Sale Transaction, he is entitled to 12 months of base salary, a pro-rated bonus, 12 months of health benefits, 12 months of time-based equity vesting acceleration, and a 12-month extension of the vested-option exercise term; on an involuntary termination in connection with or following a Sale Transaction, those benefits plus full acceleration of time-based equity awards.

Sullivan to CAO; Day retirement framed in Ex 99.1

Separately under Item 5.02, Magnite appointed Haas Sullivan, age 43, as Chief Accounting Officer and principal accounting officer, also effective October 1, 2026. Sullivan has been vice president of accounting since April 2020 after senior director and director roles at Magnite dating to 2015; earlier he was senior director of global accounting at HYLA Mobile (2010–2015) and spent five years in Deloitte & Touche’s audit practice. He will receive RSUs valued at approximately $600,000 on October 1, 2026 (four-year vest, one-year cliff) and a new severance agreement. On an involuntary termination outside a Sale Transaction, Sullivan is entitled to 3 months of base salary, a pro-rated bonus, 3 months of health benefits, 3 months of time-based vesting acceleration, and a 12-month vested-option exercise extension. On an involuntary termination in connection with or following a Sale Transaction, Item 5.02 states he is entitled to 6 months of base salary, 6 months of health benefits, full acceleration of all time-based equity awards, and a pro-rated bonus — a different CIC package than Gephart’s “foregoing plus full acceleration” structure.

Exhibit 99.1, a September 21, 2026 press release furnished with the 8-K, states that Gephart succeeds retiring CFO David Day after a decade-long tenure and that Day previously announced his retirement. CEO Michael Barrett is quoted on Gephart’s five years on the executive team. The Item 5.02 narrative itself centers on the Gephart and Sullivan appointments and compensatory arrangements rather than a dated Day departure schedule.

What this filing settles — and what it leaves open

Item 5.02 locks the September 18 appointment dates, October 1, 2026 effective dates for CFO and CAO, Gephart’s and Sullivan’s ages and role histories as stated, the $2.25 million Gephart equity split ($1,575,000 RSUs / $675,000 PSUs), Sullivan’s approximately $600,000 RSU grant, Gephart’s 12-month outside-CIC / CIC-plus-full-acceleration severance terms, and Sullivan’s distinct 3-month outside-CIC and 6-month CIC severance terms. Day’s retirement succession is stated in Exhibit 99.1. This Form 8-K does not disclose base salaries or Day’s last day.