Here’s who’s joining the S&P 500 in the index’s latest shakeup

Twilio is set to join the S&P 500 as part of the index's latest quarterly rebalancing. The change follows the pending merger between Warner Bros. Discovery, an existing index component, and Paramount — a combination that removes Warner Bros. Discovery from the benchmark.

Index membership matters because funds that track the S&P 500 must buy and sell shares to mirror the index. Additions and deletions are announced in advance but take effect on a set date, so the adjustment typically plays out around that effective date rather than at the moment of announcement. For investors, the key takeaway is that this is a mechanical change driven by index rules, not a shift in either company's underlying business.

What to watch: confirmation of the merger timeline and whether the rebalancing proceeds as scheduled. If the deal's closing date moves, the timing of index changes could shift with it. Liquidity around the effective date is also worth monitoring, since index-tracking flows can be concentrated in a short window.