Lots of people think that index funds buy on the open market. Not for a major move like Fairfax inclusion.
Exchange of stocks for units of index funds (ETFs)
Yes, there is indeed a very common (and perfectly legal) practice called in-kind creation/redemption or exchange of securities for ETF shares.
It is actually the main mechanism that allows large ETFs (SPY, VOO, QQQ, CAC 40 ETFs, etc.) to buy or sell hundreds of millions or billions of dollars/euros worth of stocks without causing massive price swings during index rebalances (such as additions to the S&P 500 or CAC 40).
How it works in practice
1. Authorized Participants (APs)
These are major banks or brokers (Goldman Sachs, JPMorgan, Société Générale, Flow Traders, Jane Street, etc.).
2. Creation Basket
Every day, the ETF issuer (BlackRock, Amundi, Vanguard, State Street, etc.) publishes the exact list of stocks (and quantities) that correspond to a fixed number of ETF units (e.g., 50,000 shares of a CAC 40 ETF).
3. In-kind exchange
• When the ETF needs to buy heavily a stock (e.g., Euronext added to the CAC 40 or Apollo added to the S&P 500), the AP:
→ Buys the stocks on the market (or takes them from its inventory),
→ Delivers this complete basket of stocks to the ETF,
→ In return, receives brand-new ETF units (creation units).
• The opposite happens when a stock is removed from the index: the AP delivers ETF units and receives the basket containing the stock to be sold.
4. Major advantages
• No cash transactions on the secondary market → very little price impact.
• Almost no taxable capital gains for the ETF (especially in the US – huge tax advantage).
• Allows absorption of colossal volumes on rebalance day without driving prices crazy.
Real-world example: Euronext added to the CAC 40 (September 22, 2025)
• CAC 40 ETFs had to buy ~€1.2 billion worth of Euronext shares.
• A large portion of that volume did not go through the regular order book.
• APs (Société Générale, BNP, Kepler, etc.) delivered Euronext shares (gradually accumulated beforehand) in exchange for millions of newly created ETF units.
• Result: the demand shock on the effective day was heavily dampened.
This answer were produce by Grok when I tried to understand how index funds trade