[cameldrv]

I don't think it's an issue of Citadel not quoting GME. In my understanding, Robin Hood is allowing purchases to close a short position, so there exist quoted prices, they just don't want people expanding a long position.

If this is coming from Robin Hood, they could make the (very weak) argument that they are protecting their retail customers from themselves, but if it's coming from Citadel, it just looks like market manipulation to me.

[jodrellblank]

I don't think it's coming from RobinHood; eToro is also blocking buys and they have the message "We have made this change following a notification from our liquidity provider that they have set $GME to close only status".

[andoriyu]

I got similar email from tasty. They said Apex clearing won't allow any new positions on meme stocks.

Given that it's not just RH, but nearly all, if not all, brokers that outsource order flow like RH...I think it's safe to assume it wasn't RH decision.