Legal

Privacy Policy

Last updated 16 October 2026

Summary

Lessons, problems and games against the AI work on your iPhone without an account. If you sign in to play online, our server keeps what it needs to run your games and ratings. There are no ads and no tracking, and we never sell your data.

Who we are

Kosumi is operated by Synton.ai LLC ("we", "us"). Contact: privacy@kosumi.app.

Stored on your device

Your games against the AI, game reviews, lesson progress, stars, streak, problem history and settings are stored in the app on your iPhone. The AI opponents and KataGo's analysis run on the device; the positions you play against them are not sent anywhere. Deleting the app deletes this data, unless you have signed in and it was synced to your account (see below).

Stored on our server

Only if you sign in:

• Account: a random account identifier, the stable user identifier Apple gives us for Sign in with Apple, your nickname, your language and, if you chose to share it, the email address Apple provides (which may be a private relay address).
• Online play: your online games (moves, clocks, result, rules, preset chat phrases), ratings and rating history, friends and friend codes, and any reports or blocks you make or receive.
• Progress sync: lesson progress, streak and problem history, so they follow you to a new device.
• Subscription status: whether your Premium subscription is active, from Apple's App Store Server API and notifications, used to unlock features and coach quotas.
• Push notifications: a device token from Apple, used to tell you when it's your turn in a correspondence game or a friend challenges you. You can turn notifications off in iOS Settings.
• Fair play: the moves of rated games may be compared with engine suggestions to detect assistance.

Our servers are hosted by a cloud provider acting on our behalf (currently Fly.io). We keep account data while your account exists and delete it when you delete your account; online games may be kept in anonymised form for rating integrity.

The coach's explanations

When you ask the coach to explain a move, the app sends position facts to our server: the board position, the move played, the move KataGo prefers, the line that follows, the points lost, which groups became weak, your approximate rank and the app language. No name, email or account details are included.

Our server passes these facts to Anthropic's API (Claude), which writes the short explanation you read. Anthropic processes them on our behalf to produce that answer and does not use them to train its models. Explanations may be cached on our server so a repeated question is answered instantly.

Sign in with Apple

Signing in is optional and only needed for online play, progress sync and Premium across devices. Apple shares a stable identifier with us and, if you allow it, your name and an email address you can hide behind Apple's relay. We don't receive your Apple ID password.

Purchases

Kosumi Premium is sold through the App Store using StoreKit. Apple processes the payment; we never see or store your card details. We receive only what Apple provides to confirm the subscription (product, status, renewal and expiry dates, and an anonymous transaction identifier).

No ads, no tracking

Kosumi contains no advertising and no third-party advertising, analytics or tracking SDKs. We don't track you across apps or websites and we don't sell or share your personal data. We may keep technical logs (such as error reports and request logs) for a short time to keep the service running and secure.

Children

Kosumi is suitable for all ages. Online chat is limited to preset phrases, and nicknames can be reported. We don't knowingly collect more data from children than described here.

Your rights and deleting your data

You can see and change your nickname in the app, and delete your account from the app's settings, which deletes your account data from our server. You can also email privacy@kosumi.app to access, correct, export or delete your data; we reply within 30 days. Depending on where you live (for example in the EU, UK or California), you have these rights by law, and you can complain to your data protection authority.

Changes

If we change this policy in a meaningful way, we will tell you in the app before the change takes effect.

Questions: privacy@kosumi.app · Synton.ai LLC