Shares of Klaviyo, Inc. (KVYO) tumbled 5.60% in after-hours trading on Tuesday following the company's announcement of a proposed secondary offering of its Series A common stock. The offering, valued at $372 million, is primarily aimed at covering tax obligations for the company's CEO and co-founder, Andrew Bialecki.

The secondary offering, which will be underwritten by Goldman Sachs & Co. LLC and Morgan Stanley, comes as Bialecki seeks to sell shares to meet tax obligations related to his stock options. This move has sparked concern among investors, leading to the sharp decline in Klaviyo's stock price during the post-market session.

While the company emphasizes that this is a pre-arranged stock sale plan for the CEO, the significant size of the offering appears to have unsettled the market. Investors may be wary of potential dilution or interpreting the insider sale as a lack of confidence in the company's near-term prospects. As trading resumes, market participants will be closely watching how Klaviyo's stock performs and whether the company can assuage investor concerns about the implications of this secondary offering.