An employer can choose to offer a two-and-a-half month grace period to spend FSA funds or allow employees to roll over a limited amount of unused funds to the next plan year, but not both.
For FSAs that permit the carryover of unused amounts, the maximum 2024 carryover amount to 2025 is $640. For unused amounts in 2023, the maximum amount that can be carried over to 2024 is $610.
Source: IRS.gov