Under the 2013 Equity Incentive Plan, the Company granted 500,000 restricted common stock awards to an officer on September 5, 2018 (the "2018 Restricted Stock Award"). The 2018 Restricted Stock Award fully vested on March 28, 2024. The 2018 Restricted Stock Award was amortized on a straight-line basis over the requisite service period. The grant-date fair value of the 2018 Restricted Stock Award was determined using the closing price of Kingsway common stock on the date of grant. Total unamortized compensation expense related to unvested 2018 Restricted Stock Award at March 31, 2024 was zero.

Under the 2020 Equity Incentive Plan, the Company has granted restricted common stock awards to certain officers of the Company (the "2020 Plan Restricted Stock Awards"). The 2020 Plan Restricted Stock Awards vest according to a graded vesting schedule and shall become fully vested subject to the officers' continued employment through the applicable vesting dates. The 2020 Plan Restricted Stock Awards are amortized on a straight-line basis over the requisite service periods. The grant-date fair values of the 2020 Plan Restricted Stock Awards were determined using the closing price of Kingsway common stock on the date of grant. During the three months ended March 31, 2024, no shares of the 2020 Plan Restricted Stock Awards became fully vested. Total unamortized compensation expense related to unvested 2020 Plan Restricted Stock Awards at March 31, 2024 was $2.4 million.

The following table summarizes the activity related to unvested 2020 Plan Restricted Stock Awards and 2018 Restricted Stock Award (collectively "Restricted Stock Awards") for the three months ended March 31, 2024:

The unvested balance at March 31, 2024 in the table above is comprised of 548,964 shares of the 2020 Restricted Stock Awards and zero shares of the 2018 Restricted Stock Award.

Stock-based compensation expense related to the Restricted Stock Awards was $0.2 million for each of the three months ended March 31, 2024 and March 31, 2023.

Ravix LLC granted 199,000 restricted Class B common unit awards to an officer of Ravix pursuant to an agreement dated October 1, 2021 ("2021 Ravix RUA"). The 2021 Ravix RUA vests based on service and the achievement of criteria based on the internal rate of return ("IRR") of Ravix.

The grant-date fair value of the 2021 Ravix RUA was estimated using the Black-Scholes option pricing model, using the following assumptions: expected term of four years, expected volatility of 75%, expected dividend yield of zero, and risk-free interest rate of 0.93%.

On October 1, 2021, 83,333 units, representing one half of the service condition for the 2021 Ravix RUA, became fully vested. The remainder of the service condition vests according to a graded vesting schedule and shall become fully vested subject to the officer's continued employment through the applicable vesting dates.

On November 1, 2022, the Company modified the inputs related to the IRR portion of the 2021 Ravix RUA to be based on the combined internal rate of return of Ravix and CSuite. The modified portion of the awards was probable of vesting both immediately before and after the modification. As a result, the fair value of the award that is subject to the IRR was measured at the modification date and compared to the fair value of the modified portion of the award immediately prior to the modification, with the difference resulting in incremental compensation expense of less than $0.1 million. The incremental fair value was estimated using the Monte Carlo simulation model, using the following assumptions at the modification date: expected term of 2.92 years, expected volatility of 72% and risk-free interest rate of 4.44%; and the following assumptions prior to the modification: expected term of 2.92 years, expected volatility of 58% and risk-free interest rate of 4.44%.

During the three months ended March 31, 2024, 5,208 units of the 2021 Ravix RUA became fully vested. At March 31, 2024 and December 31, 2023, there were 65,320 and 70,528 unvested units, respectively, of the 2021 Ravix RUA with a weighted-average grant date fair value of $3.08 per Class B common unit. Total unamortized compensation expense related to unvested 2021 Ravix RUA at March 31, 2024 was $0.2 million.

Stock-based compensation expense related to the 2021 Ravix RUA was less than $0.1 million for each of the three months ended March 31, 2024 and March 31, 2023.

Pegasus LLC granted 75,000 restricted Class B common unit awards to an officer of SNS pursuant to an agreement dated November 18, 2022 ("SNS RUA"). The SNS RUA vests based on service and the achievement of criteria based on the IRR of SNS.

The grant-date fair value of the SNS RUA was estimated using the Monte Carlo simulation model, using the following assumptions: expected term of four years, expected volatility of 85% and risk-free interest rate of 4.09%.

On November 18, 2022, 25,000 units, representing one half of the service condition for the SNS RUA, became fully vested. The remainder of the service condition vests according to a graded vesting schedule and shall become fully vested subject to the officer's continued employment through the applicable vesting dates.

During the three months ended March 31, 2024, 1,563 units of the SNS RUA vested. At March 31, 2024 and December 31, 2023, there were 41,667 and 43,229 unvested units respectively, of the SNS RUA with a weighted-average grant date fair value of $5.81 and $5.84 per Class B common unit, respectively. Total unamortized compensation expense related to unvested SNS RUA at March 31, 2024 was $0.2 million.

Stock-based compensation expense related to the SNS RUA was less than $0.1 million for each of the three months ended March 31, 2024 and March 31, 2023.

Vertical Market Solutions LLC, a subsidiary of the Company, granted 199,000 restricted Class B common unit awards to an officer of SPI pursuant to an agreement dated September 7, 2023 ("SPI RUA"). The SPI RUA vests based on service and the achievement of criteria based on the IRR of SPI.

The grant-date fair value of the SPI RUA was estimated using the Monte Carlo simulation model, using the following assumptions: expected term of five years, expected volatility of 59% and risk-free interest rate of 4.29%.

On September 7, 2023, 83,333 units, representing one half of the service condition for the SPI RUA, became fully vested. The remainder of the service condition vests according to a graded vesting schedule and shall become fully vested subject to the officer's continued employment through the applicable vesting dates.

During the three months ended March 31, 2024, no units of the SPI RUA vested. At March 31, 2024 and December 31, 2023, there were 115,667 unvested units of the SPI RUA with a weighted-average grant date fair value of $1.11 per Class B common unit. Total unamortized compensation expense related to unvested SPI RUA at March 31, 2024 was $0.1 million.

Stock-based compensation expense related to the SPI RUA was less than $0.1 million and zero for the three months ended March 31, 2024 and March 31, 2023, respectively.

(e) Restricted Common Unit Awards of DDI

DDI LLC granted 199,000 restricted Class B common unit awards to an officer of DDI pursuant to an agreement dated October 26, 2023 ("DDI RUA"). The DDI RUA vests based on service and the achievement of criteria based on the IRR of DDI.

The grant-date fair value of the DDI RUA was estimated using the Monte Carlo simulation model, using the following assumptions: expected term of five years, expected volatility of 57% and risk-free interest rate of 4.68%.

On October 26, 2023, 83,333 units, representing one half of the service condition for the DDI RUA, became fully vested. The remainder of the service condition vests according to a graded vesting schedule and shall become fully vested subject to the officer's continued employment through the applicable vesting dates.

During the three months ended March 31, 2024, no units of the DDI RUA vested. At March 31, 2024 and December 31, 2023, there were 115,667 unvested units of the DDI RUA with a weighted-average grant date fair value of $4.16 per Class B common unit. Total unamortized compensation expense related to unvested DDI RUA at March 31, 2024 was $0.4 million.

Stock-based compensation expense related to the DDI RUA was less than $0.1 million and zero for the three months ended March 31, 2024 and March 31, 2023, respectively.