The purchasers of Series A-1 redeemable convertible preferred stock also received tranche rights (Series A-1 Tranche Rights), which provided them the right to purchase additional shares of Series A-1 redeemable convertible preferred stock in an additional future tranche. This tranche was for the purchase of Series A-1 and was valued based upon the Company achieving certain future milestones and utilized a valuation model that reflected both potential outcomes of success or failure to meet the milestone.

Upon issuance in October 2020, the Series A-1 redeemable convertible preferred tranche liability was valued at $0.86 per share. There was no change in value from the date of issuance and December 31, 2020.

The Company estimated the fair value of the Series A-1 Tranche Rights using a probability-weighted present value model that considered the probability of triggering the Series A-1 Tranche Rights through achievement of the clinical development milestones specified in the Series A-1 Purchase Agreement. These estimates were based, in part, on subjective assumptions. Changes to these assumptions could have had a significant impact on the reported fair value of the Series A-1 Tranche Rights.

The following reflects the significant quantitative inputs used in the valuation of the redeemable convertible preferred stock tranche liability:


	Series A-1 Tranche Call Option
Estimated fair value of redeemable convertible preferred stock	$6.94 - $11.10
Discount rate		0.10	%
Dividend yield		0	%
Expected term (years)	0.25 - 0.45
Expected volatility	N/A
Probability of milestone achievement	80% - 100%
Strike price	$	7.80
Fair value of each tranche feature	$0.86 - $3.32

The Series A-1 redeemable convertible preferred tranche liability was settled on March 9, 2021 with the achievement of milestones set forth in the Series A-1 stock purchase agreement. The fair value of the liability was remeasured prior to settlement, resulting in the Company recognizing a loss in the consolidated statement of operations and comprehensive loss of $11.7 million during the six months ended June 30, 2021. Immediately thereafter, the balance of the redeemable convertible preferred stock tranche liability of $12.3 million was reclassified to Series A-1 redeemable convertible preferred stock.

A rollforward of the redeemable convertible preferred stock tranche liability is as follows (in thousands):


Balance at December 31, 2020	$	551
Change in fair value		11,718
Settlement upon issuance of Series A-1 redeemable convertible preferred stock		(12,269	)
Balance at June 30, 2021	$	—