People tell companion apps things they would not tell a search engine. That makes the ordinary privacy questions sharper, not different.
Expect three layers. Account data — an email address, a device identifier, purchase records — is the part every app has. Conversation data is your messages plus anything the app extracts from them into a memory or profile. Usage data covers how often you open the app, what you tap, and which features you use, usually through third-party analytics.
The second layer is the one that deserves attention. A companion transcript is a detailed record of your moods, relationships and preoccupations, and it is stored on someone else’s servers so it can be replayed into the model on your next visit. That storage is not optional — it is what makes continuity possible at all.
Vague reassurance is common; specific commitments are rarer. Look for four things. Retention: does the policy say how long chats are kept, or only that they are kept? Deletion: can you delete your account and does deletion cover conversation history, not just the login? Training: does the company say whether your conversations are used to improve models? Sharing: which third parties receive data, and for what.
A policy that answers all four is not necessarily generous, but it is honest enough to be judged. One that answers none is telling you something too.
Use an email address that is not tied to the rest of your identity. Avoid putting details in chat that would identify you in the real world — full name, employer, address, the name of your child’s school — because those end up in stored transcripts and any memory extracted from them. If the app has an editable memory, review it occasionally; you may find it has saved something you would not have chosen to store.
Before subscribing, check how billing works. Store-billed subscriptions mean the vendor never sees your card. And if you decide to leave, delete the account explicitly rather than just uninstalling — removing the app removes nothing from the server.