[rybosworld]

Yes selling will happen, and in the case of the S&P 500, it will be weighted selling across the whole index.

Spacex/Anthropic/OpenAI almost certainly won't crash the market. The most probable thing to happen is that all 3 of these rally a surprising amount on their opening day, because there will be so much forced buying of the shares.

In my opinion, the most likely bagholders will be any retail traders that buy these stocks before the lockups expire.

I think it's very likely that we see the following:

IPO day -> all 3 close higher than opening price.

1 month -> price settles into a range 20-30% higher than IPO price.

6-12 months -> price is back near IPO price +-5%. Anyone who bought and held in the first 3 months has unrealized losses.

[DanielHB]

Didn't every single large IPO in the past 15 years tanked the stock in the short term compared to the IPO time? Why wouldn't that happen again?

[rybosworld]

Not completely sure what you mean by "short term compared to the IPO time"

IPO's fairly reliably pop on day one. The performance in the first 6 months is mixed but skews slightly negative.

But the size of these 3, combined with the rule changes that are allowing them to be included in the indices much quicker than normal, means this time is very different than what we've seen before.