I am investigating buying stocks before they are added to indexes that passively managed funds are designed to track. For example, an equal weight ETF or Index, to maintain weight of its components, may rebalance periodically by buying or selling some stocks. My understanding is that announcements of additions and subtractions are made public (S&P 500 additions are made available after the market close). And the stock price likely increases/ decreases in after hours trading in response to these announcements. I am also wondering if anyone knows where (platforms? websites?) if other indices are making such announcements?