Alphabet's SpaceX bet grows 100-fold over a decade to $94 billion

SpaceX went public on June 12 at $135 a share. Its shares have since retreated from their end-June level. SpaceX closed at $146.15 on Wednesday, 8.3% above its IPO price but 14% below the June 30 close.

Sosnick told Reuters that SpaceX remains one of the most actively traded stocks among customers at Interactive Brokers, receiving a "fresh jolt of buying last week when market fears about what would happen when the first lockup expiry arrived proved to be unfounded."

Retail owners of SpaceX shares, who do not have to submit their holdings to the SEC, turned into net sellers of the stock on Friday for the first time since the IPO, according to data from Vanda Research. The research firm, which tracks the activity of self-directed individual investors, calculated that this group sold a net $4.5 million on that day. SpaceX shares were down 3% on Thursday but have risen 30% since August 5.

Alphabet held SpaceX shares worth $94 billion on June 30, according to quarterly filings, up from the $900 million investment it said it made in Elon Musk's rocket company in 2015.

Alphabet has emerged as by far the largest single institutional holder of SpaceX following its $86 billion IPO in June, according to a Reuters analysis of quarterly filings made public so far.