Earlier this month, analysts at Goldman Sachs estimated that Blackstone could attain a 0.19% weighting, implying about $15 billion of demand from index-tracking funds. Some of that buying may have already taken place: Blackstone stock has risen 9% since its inclusion was announced on Sept. 5.

Blackstone is joining after S&P Dow Jones Indices in April relented on a previous ban for new index entrants with multiple share classes.

Eoin Treacy's view

Blackstone rallied impressively over the last month in advance of its entry into the S&P500. The company’s ambitions of soon achieving the goal of $1 trillion under management and its dominant position in private credit have been the other factors that drove interest in the share.