Moderna (MRNA) will replace Warner Bros. Discovery (WBD) in the Nasdaq 100 prior to the open on Friday October 9th

Index composition changes of this kind are mechanical events with a well-established sequence: passive trackers and index-linked funds are required buyers of the incoming name and sellers of the outgoing one at the effective date, which concentrates flow into the closing print before the change takes effect and into the reopen. The inclusion trade itself tends to be anticipated well ahead of the effective date, with the bulk of any premium in the incoming name built during the run-up and a portion of it historically fading once the forced buying completes, a pattern that has recurred across prior reconstitutions and special replacements. The outgoing name faces the mirror image: forced selling from indexers, often met by active managers who have been waiting for the flow to clear. Worth noting is that the Nasdaq 100 normally reconstitutes on an annual schedule with quarterly rebalances, so an off-cycle replacement of this kind signals a trigger event such as a delisting, merger, or eligibility failure on the outgoing side; the reason for WBD's exit is the operative detail. The follow-ons are the index arbitrage positioning in the two names, the volume profile into the effective close, and any knock-on adjustments in derivative products benchmarked to the index.