Sei

Your companion in every world.

macOS Windows

v0.4.4 beta · open source · no setup

Meet your new gaming companion.

Chat and go on adventures in Minecraft together.

Experience the world together

Develop your relationship through shared experiences across different worlds.

A Sei companion standing beside the player in a Minecraft world at sunset

Thinks and feels

Each companion has their own unique personality, thoughts, and emotions.

A Sei companion exploring and reacting in Minecraft chat

Bring them to life

Design a companion's personality and appearance from scratch, or replicate your favorite characters, and get to know them.

The Sei character page where you design a companion's voice and personality

Follows you across worlds

Your relationship doesn't reset when you leave the game. Their memory of you follows them across games. Currently Minecraft, more coming soon.

The Play together game picker: Minecraft now, more games coming soon

Pricing

Self-host

Freeforever

Self-host with your own API key. Open source, yours to run however you want, entirely on your machine.

Encounter

Freelimited time

No setup needed — no API keys, no mods. Just start playing. Experience 1 hour of time together, for free.

Party

$20/ month

No setup needed. Just start playing. About 20 hours of time together, recharged every month.

FAQ

What is Sei?
Sei is an AI Minecraft companion app for macOS and Windows. Download it and summon an AI character into your world as a real second player: they explore, mine, build, and fight alongside you, and you can talk with them out loud on voice calls. Each companion has its own personality and long-term memory, so your relationship carries across sessions and into future games. There is no setup on the hosted plans, no API keys, and no config files: download, pick a companion, and start playing, with your first hour free. The app is also open source. If you prefer, self-host it for free forever with your own API key or a local model, entirely on your machine.
Does my companion remember me?
Yes. Each companion keeps a long-term memory of your time together, and it follows them across sessions and from one game to the next. Memories stay on your machine.
Which games can we play?
Today, Minecraft. More games are coming, and because their memory follows them, the same companion will come with you into the next one.
Do I need to set anything up?
No. There's no setup: download Sei, pick a companion, and they join your Minecraft world. No API keys, no mod loaders, no config files. If you'd rather run everything yourself, the free self-host mode uses your own API key or local model.
Is Sei open source?
Yes. The Sei app is open source — the code is on GitHub. Self-host it for free with your own model, or use our hosted service and skip the setup entirely.
Is it private?
In local mode, Sei runs entirely on your machine and nothing leaves your computer. If you use our cloud services, only your chat is forwarded to our model provider so the companion can reply. Memories never leave your machine.

Your companion in every world.

macOS Windows