What you need
- An iPhone with 6 GB of RAM or more. The model needs that much memory to run. Check your model's spec if you're unsure.
- About 2 GB of free storage for the model, downloaded once when you first open the app. You can delete it later to get the space back.
- A connection for setup only. After the download, chatting works in airplane mode.
If your iPhone has less memory, this app isn't for you yet, and we'd rather say so up front than send you a bad first experience.
What "private" means here
Replies are generated on the phone, and your chats never leave it. There's no account, so there's no profile to tie them to. We're careful with the claim: the app does send anonymous usage analytics (things like which screens get used), not your messages. Our private AI chat page goes into more detail.
How it compares
Most of the other apps people find when they search for private AI are general assistants. Castmates is built for character roleplay. That's the main difference, and it comes with trade-offs.
| Cloud apps (Character.AI, Replika) | Other on-device apps (Enclave, Locally AI, PocketPal) | Castmates | |
|---|---|---|---|
| Where the AI runs | Their servers | Your phone | Your phone |
| Chats leave the phone | Yes | No | No |
| Account | Usually | Varies by app | None |
| Works offline | No | Yes | Yes, after the download |
| Built for characters and stories | Yes | Mostly general assistants or model runners | Yes, 35 characters |
| Model quality | Largest, most capable | Small, you may pick the model | Small, tuned for roleplay |
| Phone needed | Almost any | Recent iPhone | 6 GB+ RAM iPhone |
Cloud apps win on raw capability and on running anywhere. The on-device apps are good if you want a private general assistant, or to try different open models yourself (PocketPal is built for that). Castmates is the option when what you want is a character who stays in role, with the conversation staying on your phone. We haven't tested every feature of the other apps, so check their listings for current details.
What the roleplay is like
There are 35 characters across 8 genres and 127 ready-made scenarios, so a session starts mid-story instead of from a blank box. Pro lets you build your own characters. You can meet the cast before you install anything.
Cost
Free to start with 30 messages a day. Pro is $6.99 a month, $29.99 a year or $44.99 once, billed by Apple.