6. Leases

The Company has entered into operating leases primarily for commercial buildings. These leases have terms which range from 3 years to 11 years, some of which include options to extend the leases for up to 5 years. Rent expense, including short-term lease cost, was $4,017, $3,870, and $4,095 for the years ended December 31, 2023, 2022 and 2021, respectively. Operating lease right-of-use assets and liabilities commencing after January 1, 2019 are recognized at commencement date based on the present value of lease payments over the lease term. The operating leases do not contain material residual value guarantees or material restrictive covenants.

In July 2023, the Company entered into an Assignment and Assumption of Lease Agreement in which a third party (Assignee) assumed the rights, title, and interest in the lease, including assumption of lease payments. As inducement for the Assignee to enter into the agreement, the Company paid an incentive of $395, provided for four months of free rent for the period October 1, 2023 through January 31, 2024, and conveyed ownership of certain items of the facility's furniture and equipment. Commencing February 1, 2024 and ending May 31, 2031, the Assignee assumes responsibility for the monthly lease payments. Notwithstanding the Assignee's assumption of lease payments, Inogen remains the primary obligor under the lease to the landlord. The Assignee gained control to the facility on September 29, 2023, and related sublease income was not material.