Russell shifts to an annual rebuild (1989)
FTSE Russell's predecessor moved the index rebuild from twice a year to once, in June. The annual cadence then held for more than three decades as index funds grew from a niche product into a market force.
The single June rebuild became a fixed event on every trader's calendar.
Reconstitution day grew into one of the year's highest-volume sessions as passive money ballooned.
The 2026 change reverses a 37-year-old decision, returning to the twice-a-year rhythm the index left behind in 1989.
