Twilio (TWLO) and Vylor (VYLR) are to be added to the S&P 500

Index additions follow a well-worn mechanical sequence: announcement, a gap higher on the headline, then passive accumulation into the effective date as benchmark-tracking funds are required holders regardless of view. The flow is predictable in direction but not in magnitude, since what matters is the size of the index-linked AUM obliged to buy against the free float and the existing shareholder register's willingness to supply. Historically the announcement-to-effective window has tended to see the names outperform, with part of the move given back after the rebalance once the forced bid disappears, a pattern repeated across prior S&P 500 inclusions. The other side of the trade is the deletions and the funding leg: index changes of this kind typically come with removals, and the spread between additions and deletions is where the rebalance-day volume concentrates. Worth noting is that S&P 500 inclusion has historically carried a liquidity and coverage premium beyond the passive flow itself, as eligibility broadens the natural buyer base. The follow-ons are the effective date, the accompanying deletions, and any index-change volumes print at the close on rebalance day.