Do I need to inform my opponent how many cards I am sideboarding?

Ruling: You do not need to inform your opponent of how many cards you are swapping during sideboarding.

Nuances:

• At high level play, you should avoid letting your opponent know how many cards you are sideboarding
• At the highest level, you can shuffle your main deck and sideboard together then remove 8 cards to prevent your opponent from seeing how many cards you sideboard (if any)
• This prevents giving information about deck configuration changes that could reveal whether you're planning to go first or second