Under the 2022 Stock Incentive Plan (the 2022 Plan), up to 6.8 million shares of common stock are available for awards to our employees, officers, consultants, and directors. Awards may be in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, performance share units, and other stock-based awards. Each award, under the 2022 plan is counted as 1.00 share. The exercise price for stock options issued cannot be less than the fair value of the underlying common stock as of the grant date. The maximum term of each stock option or stock appreciation right is ten years after the date of grant. At December 31, 2023, approximately 5.9 million shares were available for future grants under the 2022 Plan.

Under the Stock Incentive Plan of 2017 (the 2017 Plan), which was terminated in May 2022 for the purposes of any further grants, up to 17.0 million shares of common stock were available for awards to our employees, officers, consultants, and directors. Awards could be in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, performance share units, and other stock-based awards. Each full-value award under the 2017 plan, defined as any award other than a stock option or stock appreciation right, were counted as 1.76 shares. Awards granted before the termination of the 2017 Plan remain outstanding in accordance with the plan's terms. Any shares subject to an outstanding award under the 2017 Plan that, after March 15, 2022, is not issued because the award is forfeited, terminates, expires or lapses without being exercised (as applicable), or is settled for cash, becomes available for issuance under the 2022 Plan. Stock options had a term of eight years after the date of grant and fully vested after three years.

SSUs are classified as equity. As of December 31, 2023 and 2022, there were 105 thousand shares and 208 thousand shares, respectively, of SSUs outstanding with a weighted average grant date fair value of $18.78 per share. There were no issuances of SSUs during 2023, 2022, or 2021. SSUs vest over a six year period, beginning at the date of grant. One-third of the SSUs are eligible for accelerated vesting on a cumulative basis at the end of each of the one-, three-, and five-year service periods that began on January 1, 2021, if certain performance goals are achieved. Forfeitable dividends on SSUs are accrued in the form of cash. Compensation cost for SSUs subject to accelerated vesting due to the achievement of certain performance conditions at the end of the one-, three-, and five-year service periods is recognized over the implicit service period.

The total fair value of SSUs that vested during both 2023 and 2021 was $1.9 million. No SSUs vested during 2022. At December 31, 2023, we had $0.7 million of unrecognized compensation cost related to SSUs that will be recognized over a remaining weighted average period of 1.05 years. No SSUs were forfeited during 2023.

PSUs are classified as equity. There were no new tranches of PSUs issued during 2023, 2022, or 2021. Vesting for the PSUs occurred at the end of a three-year period and was contingent upon our achievement of prospective company performance goals and our total shareholder return relative to a board-approved peer group during the three-year period. Actual performance, including modification for relative total shareholder return, could have resulted in the ultimate award of 40 percent to 180 percent of the initial number of PSUs issued, with the potential for no award if company performance goals had not been achieved during the three-year period. Forfeitable dividend equivalents on PSUs were accrued as cash.

PSU shares represent aggregate initial target awards and accrued dividend equivalents and do not reflect potential increases or decreases resulting from the application of the performance factor determined after the end of the performance periods. At December 31, 2022, the three-year performance period for the 2020 PSU grant was completed and the related shares vested, but the performance factor had not yet been applied. The performance factor, which exceeded 100 percent, was applied during the first quarter of 2023 and resulted in the granting and vesting of an additional 245 thousand shares. We had no outstanding PSUs at December 31, 2023 or 2022 and there were no PSUs forfeited during 2023.

The total fair value of PSUs vested during 2023, 2022, and 2021 was $5.8 million, $4.2 million, and $6.6 million, respectively. At December 31, 2023, we had no unrecognized compensation cost related to PSUs as there are no remaining PSUs outstanding. The estimated compensation expense was adjusted for actual performance experience and was recognized ratably during the service period when it became probable that the performance conditions would be satisfied. Compensation cost for PSUs subject to accelerated vesting at the date of retirement eligibility was recognized over the implicit service period.


	Year Ended December 31, 2020

Expected Volatility (based on our and our peer group historical daily stock prices)	23	%
Expected Life (equals the performance period)	3 years
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	0.85	%

CIUs are denominated and settled in cash, with each unit representing the right to receive one dollar. Vesting for the CIUs occurs at the end of a three-year period and is based upon prospective company performance measures and our total shareholder return relative to a board-approved peer group during the three-year period. We originally issued 9.0 million, 8.0 million, and 7.2 million CIUs during 2023, 2022, and 2021, respectively. However, actual performance, including the modification for relative total shareholder return, may result in an award of up to 200 percent of the initial number of CIUs issued.

1CIUs in the preceding table do not reflect potential increases or decreases resulting from the application of the performance factor determined after the end of the performance periods. At December 31, 2023, the three-year performance period for the 2021 CIU grant was completed and the related awards vested, but the performance factor has not yet been applied. The performance factor will be applied during the first quarter of 2024, with payment of the awards at that time.

The liability recorded in connection with CIUs at December 31, 2023, 2022, and 2021 was $37.7 million, $16.0 million, and $3.2 million, respectively. There were no CIU payments made during 2023, 2022, and 2021. We had approximately $3.4 million of unrecognized compensation cost related to CIUs that will be recognized over a weighted average period of 1.7 years. The estimated compensation expense is adjusted for actual performance experience and is recognized ratably during the service period, or remaining service period, if and when it becomes probable that the performance conditions will be satisfied. Compensation cost for CIUs subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period.

The fair value of CIUs is estimated at each reporting period using the Monte-Carlo simulation model. Key assumptions used to value CIUs granted are as follows:


	Assumptions as of the Year Ended December 31, 2023
	2023 Grant		2022 Grant
Expected Volatility (based on our and our peer group historical daily stock prices)	30	%	27	%
Expected Life (equals the performance period)	2 years		1 year
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	4.26	%	4.75	%


	Assumptions as of the Year Ended December 31, 2022
	2022 Grant		2021 Grant
Expected Volatility (based on our and our peer group historical daily stock prices)	30	%	33	%
Expected Life (equals the performance period)	2 years		1 year
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	4.26	%	4.60	%


	Assumptions as of the Year Ended December 31, 2021
	2021 Grant
Expected Volatility (based on our and our peer group historical daily stock prices)	50	%
Expected Life (equals the performance period)	2 years
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	0.71	%

RSUs vest over a one to three-year service period, beginning at the date of grant, and the compensation cost is recognized ratably during the vesting period. Forfeitable dividend equivalents on RSUs are accrued as cash. Compensation cost for RSUs subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period.

The total fair value of shares vested during 2023, 2022, and 2021 was $49.9 million, $28.0 million, and $23.9 million, respectively. At December 31, 2023, we had $26.0 million of unrecognized compensation cost related to RSUs that will be recognized over a weighted average period of 0.9 years.

Cash-settled RSUs vested over a one to three-year service period, beginning at the date of grant, and the compensation cost was recognized ratably during the vesting period. Forfeitable dividends on cash-settled RSUs were accrued in the form of cash. Compensation cost for cash-settled RSUs subject to accelerated vesting at the date of retirement eligibility was recognized over the implicit service period.

The amount payable per unit awarded is equal to the price per share of Unum Group's common stock at settlement of the award, and as such, we measured the value of the award each reporting period based on the current stock price. The effects of changes in the stock price during the service period were recognized as compensation cost over the service period. Changes in the amount of the liability due to stock price changes after the service period were recognized as compensation cost during the period in which the changes occurred. The liability recorded in connection with cash-settled RSUs at December 31, 2022, and 2021 was $0.8 million and $0.5 million, respectively. There was no remaining liability for cash-settled RSUs at December 31, 2023. Cash-settled RSU payments made during 2023, 2022, and 2021 were $1.1 million, $0.6 million, and $0.6 million, respectively. At December 31, 2023, we had no unrecognized compensation cost related to cash-settled RSUs as there are no remaining cash-settled RSUs outstanding.


	Year Ended December 31
	2023		2022		2021
	(in millions of dollars)
Performance Share Units	$	0.3	$	5.7	$	3.3
Cash Incentive Units	21.7		12.8		3.2
Restricted Stock Units and Cash-Settled Restricted Stock Units	40.6		32.7		25.5

Stock Success Units	0.9		0.9		2.8
Other	0.6		0.6		0.6
Total Compensation Expense, Before Income Tax	$	64.1	$	52.7	$	35.4

Total Compensation Expense, Net of Income Tax	$	57.5	$	47.3	$	31.1