Slack's stock price ended up at $38.62 a share on its first day on the market after reaching a high of $41.95 on a busy Thursday.
Shares of the company began trading shortly after 9 a.m. PT on the New York Stock Exchange for $38.50 and saw an immediate jump in price to more than $40.
Its reference price was $26 under the ticker symbol WORK in a direct listing.
A direct listing is different from an IPO in that only existing shares owned by employees and investors are sold, without the involvement of underwriters.
The reference price doesn't reflect the shares' offering price or opening public price but instead is a point of reference for investors.
A designated market maker determines the price based on comparing the ranges of buy and sell orders.