9. Warrants

In connection with certain of its redeemable convertible preferred stock issuances, convertible debt financings, and other financing arrangements the Company had issued warrants for shares of its common stock and various issues of its redeemable convertible preferred stock. Such warrants related to its redeemable convertible preferred stock had been recorded as liabilities as a result of non-standard anti-dilution and redemption rights of the underlying stock and were carried at their estimated fair value using the Monte Carlo valuation model. As of February 14, 2014, the warrants were converted to common stock warrants with no anti-dilution features.  The Company revalued the warrants as of the offering date, recorded a gain on the liability through the Statements of Operations, and subsequently reclassified the warrant liability to additional paid-in-capital.

The former Series E redeemable convertible preferred stock warrants convert directly to common stock equivalents with a conversion rate of $2.69244 for a total of 11,367 shares of common stock.  The common stock warrants outstanding convert on a one-to-one basis of every warrant to common stock, therefore the 161,295 warrants outstanding as of March 31, 2014 could be exercised into a total of 172,662 shares of common stock.

A summary of outstanding common stock warrants at March 31, 2014 is as follows:

A summary of outstanding warrants at December 31, 2013 is as follows:

The fair value of the preferred stock warrant liability was $0 and $260 at March 31, 2014 and December 31, 2013, respectively. During the three months ended March 31, 2014 and March 31, 2013, the Company recorded a gain of $36 and $20, respectively, on the change in fair value of the preferred stock warrants. The liability was reclassified to additional paid-in-capital as of February 14, 2014, and the warrants were converted to common stock warrants.