Most major indexes weight companies by the amount of stock that is available to trade in the market — not total market cap. So SpaceX’s multi-trillion-dollar valuation doesn’t directly translate to a large weighting right away. SpaceX’s initial position in either the S&P 500 or Russell 1000 is expected to be roughly 0.1%. That weighting could grow over time as lockup periods expire and more shares become freely tradable.