Terms of Use

Applies to the Stackflight iOS app. Last updated 21 September 2026.

1. The agreement

These terms are between you and Anton Romanyuk (Vacuumbreather), the developer of Stackflight. By downloading or using the app you accept them.

Stackflight is distributed through Apple's App Store, so Apple's Licensed Application End User License Agreement also applies, and prevails over anything here that conflicts with it. You can read it at apple.com/legal/internet-services/itunes/dev/stdeula. Apple is not a party to these terms, and Apple is not responsible for the app or for supporting it.

2. What you get

Stackflight is a finite course about how large language models work. A substantial part of it — the Foundation track and Track 01 — is free with no time limit and no quota.

A single in-app purchase, Stackflight Pro, unlocks the remaining course content. It is a non-consumable one-time purchase, not a subscription: it does not renew, it does not expire, and there is nothing to cancel. It can be restored on any device signed in to the same App Store account, either automatically on first launch or with the Restore purchases button on the Profile screen.

Because the app has no accounts, a purchase is tied to an App Store account rather than to a person. It cannot be transferred between App Store accounts, and it holds on one device at a time — restoring it on a second device moves it there.

3. Price and payment

The price is shown in the app before you buy, in your local currency, and is charged by Apple to your App Store account. The launch price is an introductory price and will rise later; a price change never affects a purchase already made.

4. Refunds

Purchases are made through Apple, so refunds are handled by Apple and not by us. Request one at reportaproblem.apple.com. We have no ability to issue or refuse a refund on Apple's behalf. If a refund is granted, the course locks again; anything you have already learned, and your XP, streak and progress, are untouched.

5. What you may and may not do

You may use Stackflight for your own learning, including at work. You may not redistribute, resell, sublicense or publish the course content, narration or exercises, in whole or in substantial part, and you may not attempt to extract the bundled audio or content for redistribution. The course text, audio, artwork and software remain our property.

6. What the course is, and is not

Stackflight is educational material. It explains how language models behave and how to work with them, and it deliberately includes examples of systems failing. It is not professional, legal, security or engineering advice for your particular system, and following it is not a substitute for your own testing and judgement. You remain responsible for what you build.

7. Availability and changes

The app runs offline and does not depend on a server, apart from validating a purchase.

We intend to keep the course current: correcting, sharpening and adding lessons as the field changes. Anything added to the course is included in the purchase you have already made, at no extra cost and with no second purchase to unlock it. We do not commit to a schedule or to any particular future lesson, and we may also change or remove content. If content is removed, anything you have already mastered stays unlocked.

8. Warranty and liability

The app is provided "as is", without warranty of any kind, to the extent the law permits. Nothing in these terms limits liability for death or personal injury caused by negligence, for fraud, or for anything else that cannot lawfully be limited. Subject to that, our total liability arising out of the app is limited to the amount you paid for it.

Your statutory rights as a consumer are not affected by anything in these terms.

9. Privacy

The app has no accounts and collects no analytics. What it stores, and the two things that can leave your device, are set out in the privacy policy.

10. Contact

Questions, problems and support: anton.romanyuk@vacuumbreather.com. If your question is about a purchase, include the Support ID shown under Profile → Settings — it is the only way to identify a purchase when there is no account.