> Anthropic, OpenAI and SpaceX could well amount to $4T+ in market cap. That's ~6% of the entire index. It's like adding another NVidia.

This is a common misconception. The S&P 500 weights allocation by float-adjusted market cap, not by total market cap. In the case of SpaceX, they are planning to float ~4% of shares at IPO. Even if SpaceX was added to the index, its index weight would be based on that tiny float, and at a $1.75T valuation it would be treated as roughly a $70 billion company.

SpaceX weight would be ~0.125% of the index, not ~2.5% as you imply.

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HWR_14 4 hours ago | parent | next [-]

SoaceX plans to continually unlock float for the first six months of being listed. So the percentage of the index would continue to rise.

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Xixi 4 hours ago | parent | prev [-]

Nasdaq "solved" that problem by including a 5x float multiplier for stocks with less than 20% of shares available to the public...

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tristanj 4 hours ago | parent [-]

That's misleading.

Before the changes, the Nasdaq-100 index was total market cap-weighted not float-weighted. Once a company crossed 10% floated shares, the company was added to the index at full weight.

Nasdaq's new system is a hybrid of float-weighted and cap-weighted. If a company has below 33.3% float, its weighting is 3x float. Above that, it's cap weighted. This allows a gradual fade-in of the company into the index.

It's a better system than the previous one, and in Nasdaq's own words, more conservative.

For the Nasdaq-100, SpaceX at 4% float gets 3 x 4% = 12% of its market cap counted, which is $210B not $1.75T. Still <1% of the index.

Also, the multiplier is 3x, not 5x. Nasdaq proposed 5x, but after feedback, this was reduced to 3x. The new thresholds are 3x and 33%, not 5x and 20%.

https://www.nasdaq.com/newsroom/nasdaq100-index-methodology-...

	▲	Xixi 4 hours ago \| parent [-]
		I stand corrected, I was not aware of the full mechanism, and I was still stuck at the proposed multiplier and not the actual one.