Well Coinbase has an institutional service as well, I believe called Coinbase Prime. Microstrategy bought their 70k BTC through Coinbase Prime. I don't know how Grayscale does their buys but they aren't even buying right now so it definitely wasn't them. It must've just been some big institutional client(s) of Coinbase's. Goes to show that as much as Grayscale is publicly showing the institutional demand for Bitcoin each week with their investment reports, there's a lot more institutional demand coming in besides just Grayscale. And the institutional flood is still only just starting, right now it's only the most forward thinking 1% of institutions starting to nibble on Bitcoin.
I also think that Grayscale doesn't really have that much money to invest into bitcoin all at once, they have invested nearly that much money for the past 1 year, to do as much of it in just one day would be a suicidal decision by them.
Plus they are on a great trajectory to make so much money as of right now with the amount of bitcoin they have, they do not need to put anything at risk, they have doubled their billion dollars in 2020, isn't that sort of enough?
If they get involved at this place it is going to get harder and harder, and with a drop they could be in a huge whole if they bought here, but if they stay away, they could still profit even after a fall. It could be anyone but I think anyone who has spent 1.5 billion dollars on 30k or more right now must be thinking too much further ahead, and not anytime soon, since we can't really double that quickly anymore.
Grayscale doesn't work like that though. Investors give them money to buy Bitcoin, and in return Grayscale gives them shares worth that amount of Bitcoin. Grayscale just buys based on how much investors give them each day. The last three days of their 6 month investment period (dec 22,23,24) they bought up about 30k BTC combined, which is a massive amount (over $700 million) because no doubt investors were trying to get in just before Grayscale's 6 month investment period ended before they closed up for a few weeks - every 6 months they stop taking investments and close up for a few weeks, the 6 month period is a lockout period in which investors can't sell the shares they bought up during that time, but once the lockout period ends investors can sell the shares on the open market, and for whatever reason Grayscale shuts down investments for a few weeks at the end of each lockout period.
They aren't a managed fund that decides what investment moves to make on behalf of their investors and they aren't a corporation that is investing their cash into Bitcoin, they just buy BTC whenever their investors give them money to do so, which they then own and hold while giving shares pegged to the BTC price to their investors who can later sell them on the open market. And the way they make money is on the fees and premium they charge, meanwhile they own an enormous amount of Bitcoin to which their shares are pegged. Drops in price don't directly affect Grayscale at all, they just make money off the fees they charge their investors.
But yeah for sure these institutions that are buying up so much BTC, like that $1.5 billion that exited Coinbase the other day, are buying for the long term.