Material Event (Form 8-K)

On September 8, 2025, Sierra Pacific Power Company (the "Company"), completed the sale of $450 million in aggregate principal amount of its 6.200% Fixed-to-Fixed Reset Rate Junior Subordinated Notes, SPPC JSN Series 2025A, due 2055 (the "Notes") pursuant to an Underwriting Agreement, dated September 4, 2025, between the Company and the underwriters named therein (the "Underwriters"). The Underwriting Agreement contains certain customary representations, warranties and covenants concerning the Company and the registration statement relating to the offering of the Notes. In addition, the Company has agreed to indemnify the Underwriters against certain liabilities, including liabilities under the Securities Act of 1933, as amended, and the Securities Exchange Act of 1934, as amended.

The Notes were issued pursuant to an indenture, by and between the Company and The Bank of New York Mellon Trust Company, N.A., as Trustee, dated September 8, 2025 (the "Base Indenture"), as supplemented by a first supplemental indenture, dated September 8, 2025 (the "First Supplemental Indenture" and, together with the Base Indenture, the "Indenture"). The Company intends to use the net proceeds from the sale of the Notes to fund capital expenditures and for general corporate purposes.

The Notes will bear interest (i) from and including September 8, 2025 (the "Original Issue Date") to, but excluding, December 15, 2030 (the "First Reset Date") at the rate of 6.200% per annum and (ii) from and including the First Reset Date, during each Reset Period (as defined in the Indenture) at a rate per annum equal to the Five-year U.S. Treasury Rate (as defined in the Indenture) as of the most recent Reset Interest Determination Date (as defined in the Indenture) plus a spread of 2.549%, to be reset on each Reset Date (as defined in the Indenture), and will mature on December 15, 2055. Interest on the Notes will be payable semi-annually in arrears on June 15 and December 15 of each year, beginning on December 15, 2025.

The Company may redeem some or all of the Notes, at its option, in whole or in part (i) on any day in the period commencing on the date falling 90 days prior to the First Reset Date and ending on and including the First Reset Date and (ii) after the First Reset Date, on any interest payment date, at a redemption price in cash equal to 100% of the principal amount of the Notes being redeemed, plus, subject to the terms of the Indenture, accrued and unpaid interest on the Notes to be redeemed to, but excluding, the redemption date. The Company also may at its option redeem the Notes, in whole but not in part, (a) for a period of 120 days following the occurrence of a Tax Event (as defined in the Indenture) at a redemption price in cash equal to 100% of the principal amount of the Notes, plus, subject to the terms of the Indenture, accrued and unpaid interest on the Notes to, but excluding, the redemption date, and (b) for a period of 120 days following the occurrence of a Rating Agency Event (as defined in the Indenture) at a redemption price in cash equal to 102% of the principal amount of the Notes, plus, subject to the terms described in the Indenture, accrued and unpaid interest on the Notes to, but excluding, the redemption date.

The Notes will be unsecured obligations and will rank junior and subordinate in right of payment to the prior payment in full of the Company's existing and future Senior Debt (as defined in the Indenture). The Notes will rank equally in right of payment with any future unsecured indebtedness that the Company may incur from time to time if the terms of such indebtedness provide that it ranks equally with the Notes in right of payment.

The foregoing descriptions of the Underwriting Agreement, the Base Indenture and the First Supplemental Indenture do not purport to be complete and are qualified in their entirety by reference to the full text of the Underwriting Agreement, the Base Indenture and the First Supplemental Indenture, copies of which are filed as Exhibits 1.1, 4.1 and 4.2, respectively, hereto and are incorporated by reference herein.