EasyJet and Ithaca Energy will join Britain's FTSE 100 index after FTSE Russell's September quarterly review of the FTSE UK index series. Ithaca's inclusion marks a milestone for the North Sea oil producer following expansion through acquisitions. The companies will replace betting group Entain and homebuilder Persimmon, which will move to the FTSE 250 alongside Pinewood Technologies, Seraphim Space Investment Trust and Volex. Aston Martin and GB Group will leave the FTSE 250. The changes will be implemented at the close of business on September 18 and take effect on September 21, 2026. The reshuffle follows Apollo Global's August agreement to buy EasyJet for about £5.70 billion ($7.69 billion).