The news, reported by All Things D, is a surprising development considering that Twitter just closed a $200 million round of funding in December led by the senior firm Kleiner Perkins Caufield & Byers, and Andreessen Horowitz did not participate in the round. That round put Twitter's valuation at $3.7 billion.
With Twitter now estimated to be worth $4 billion, Andeessen Horowitz's $80 million stock buy equates to roughly 2% of Twitter. While not a bargain buy, Andreessen's gamble will payoff handsomely should Twitter's valuation continue to skyrocket.
Firm partners Marc Andreessen and Ben Horowitz were not immediately available for comment. "Sources said that the firm made the move because it is already deeply invested in other key companies in the social space," according to All Things D.