Until now, Brave said your Leo AI conversation history stayed only on your own device and was never saved elsewhere. The policy now says that if you enable Brave Sync, that conversation history is also stored on Brave's Sync servers (in encrypted form) so it can follow you across devices. Even though it's optional and encrypted, this is a new way your chat data can be stored off your device, which it couldn't before.
“Conversation history is stored locally on your device and (if you enable it) securely included in [Sync]().”
What you can do — If you want your Leo conversations to stay only on the device you're using, don't enable Leo/chat history in Brave Sync settings, or check brave://settings/leo-ai to confirm history sync is off.