> At some point the S&P will have to say the market itself has spoken and likely capitulate

It really doesn't. The S&P 500 is an opinionated index. If you want total market, buy a total-market index.

My guess is S&P will stick to its guns, Anthropic will season in, and SpaceX and OpenAI (if it goes public) will stay outside for a few years.

They can certainly say they no longer track the 500 leading large-cap companies on the US exchanges.

The S&P 500® is widely regarded as the best single gauge of large-cap U.S. equities. The index includes 500 leading companies and covers approximately 80% of available market capitalization.