Is it free? Yes, and open source under the MIT licence. There is no paid version and nothing to sign up for.
Does it need my Instagram password? No. It uses the session you are already logged in with on instagram.com, the way the Instagram website does. It never sees your password.
Does anything get sent to you? No. There is no server. The only traffic is between your browser and Instagram's own servers.
Can I save my whole inbox? Yes. Click Several chats, or the whole inbox, pick Inbox and Message requests, and tick Every chat.
Does it keep photos and voice notes? Yes, as real files beside the messages, fetched while Instagram's links are still valid. Untick the option for a quick text-only export.
How do I read a saved chat? Unzip it and open index.html in any browser. It works offline, with search, dates, filters and a gallery.
Can I keep only some dates? Yes. Set From and To before exporting, for one chat or many.
Can I download only new posts? Yes. Tick Only what I haven't downloaded yet. Kept remembers what each export saved, per account.
What about private accounts? You can save what your account can already see: public accounts, and private ones you follow.
Will Instagram mind? Kept uses your normal session and paces its requests a little under a second apart, waiting when Instagram asks it to slow down. It reads; it never posts, likes or follows.
Which browsers? Chrome, Brave, Edge and other Chromium browsers on a computer, and Firefox 140 or later (new, from the release page). Not Safari or phones yet. The interface speaks English, Bangla, Arabic and Spanish.
Something broke? Click Check Instagram in the popup or the Export Center, then Report a problem. It opens a GitHub issue with the details filled in, usernames removed, for you to review.