Play chess with an AI friend who talks with you

Sei is an AI gaming companion: a free desktop app for Mac and Windows. Your companion sits across a 3D chess board from you. They play like a real person at their own level, talk with you while you play, and remember the game next time.

macOS Windows

Free to start · Open source

A 3D chess board in the Sei app during a voice call with the companion Marv, who is thinking about his move — A game with Marv on a voice call. The move list sits in the corner and the call controls along the bottom.

How it works

Open a chat with your companion. Press the Play together button at the top and pick Chess.
Pick a side. Choose White, Black, or Random, then press Launch. Your first game downloads a small move model (about 21 MB) once.
Play and talk. Move your pieces on the board. Type in the chat or start a voice call. Your companion plays their moves and talks with you when they have something to say.

An AI chess companion, not a chess engine

Most chess bots are engines with a strength slider. Sei's chess is built the other way around: it starts from a character, and the chess follows from who they are.

Moves like a person. Moves come from Maia-3, a model trained on human games to predict what a player at a given rating would play. Sei adds the slips people make at that level, like missed tactics and the odd blunder.
Plays in character. Your companion chooses from a few human moves the one that fits their personality. A careful character plays carefully. A show-off goes for the flashy option.
Strength from their personality. On your first game, Sei sets a strength between 400 and 2000 Elo and a play style from your companion's persona. You can change both in Edit companion, under Games.
Meets you where you are. If you lose, the next game is a little easier. If you win, it gets a little harder. This only applies while the strength is on Auto.
Talks, but not too much. They answer you, react to a good move, offer a draw, or concede a lost game. They do not narrate every move.
Remembers you. Finished games are saved in your chat with a move-by-move replay. Your companion can save what mattered to long-term memory and bring it up later.

The Sei 3D chess board with wooden pieces at the starting position — The board is untimed. Take as long as you like.

How strong should they be?

On Auto, Sei reads your companion's personality and picks a strength that fits it. Most characters land between 600 and 1400. As a rough guide:

400 to 700	Barely knows the rules.
800 to 1100	A casual player.
1200 to 1500	A club player.
1600 to 2000	A strong player. 2000 is as fierce as it gets.

To set it yourself, open Edit companion, go to Games, and switch Chess to Custom. You get a slider from 400 to 2000 in steps of 50, and a box where you can describe their play style in your own words, like "loves early queen attacks" or "trades everything off and grinds endgames." On Auto, the strength moves with your results but stays close to the character: it never drops more than 600 below or rises more than 200 above where it started. Draws, and games resigned before the third move, do not change it.

Where the moves come from

The moves are worked out on your computer. Sei's open source engine, cce-1, runs the Maia-3 model locally and lets it suggest a few moves a person at that rating would play, with the slips a person at that level makes. A small copy of Stockfish runs alongside it only to spot tactics and judge who is ahead; it never picks the move. Your companion then chooses among those few candidates, so their personality decides the style of the game, not how strong it is. If the AI call for that choice fails, the engine plays its top candidate itself, at the same strength.

On the board

Click a piece and then a square, or drag it. Dots and rings show the legal moves.
Right-click and drag to draw arrows and circles while you plan.
The last move and any check are highlighted. Pick your piece when a pawn promotes.
Flip the board, see captured pieces, and scroll back through the move list.
Full rules: castling, en passant, promotion, and draws by stalemate, threefold repetition, insufficient material, the 50-move rule, or agreement.
Leave in the middle of a game and it is waiting for you when you come back. Each companion has one game going at a time.

What your companion says

They talk about the game the way a friend across the table would: a groan at a lost knight, a jab when you take too long, a worry about their king. They never read out squares or notation, and they do not announce their moves. If you go quiet for a while on your move, they may nudge you once. Several quick messages from you get one reply, and when the game ends they react to how it went.

Who it is for

Sei is for a casual game with a friend who has opinions about it. It does not analyze your games, give lessons, offer hints or takebacks, export PGN, or track a rating. There are no time controls and no games against other people. If you want to train seriously, a dedicated training site or an AI chess coach will suit you better. If you want someone to play with, who plays like a person and talks with you, that is what this is for.

The same companion in every game

Chess is one way to play with your Sei companion. The same character, with the same memory of you, also joins your Minecraft world as a real player, farms beside you in Stardew Valley, takes turns drawing in Draw!, and with Backseat watches you play anything else. See all of Sei.

Requirements

Computer	macOS (Apple Silicon or Intel) or Windows
Download	A one-time move model of about 21 MB, fetched on your first game
Strength	400 to 2000 Elo. Auto from the persona, or set by you.
Clock	None. Games are untimed.
Voice	Optional. Type in the chat or talk on a voice call.

Questions

How strong is my companion at chess?

Somewhere between 400 and 2000 Elo. The first time you play, Sei picks a strength and a play style from your companion's personality. On that setting, the strength follows your results, within limits: after you lose, the next game is 100 points easier, and after you win, it is 50 points harder. You can also set the strength and style yourself in Edit companion, under Games.

Does it play like a person or like a chess engine?

Like a person. Moves come from Maia-3, a model trained on human games to predict what a player of a given rating would play. Sei adds the slips people make at that level, such as missed tactics and the odd blunder. Your companion then picks the move that fits their personality from a few human options.

Can I talk to my companion during the game?

Yes. Type in the chat next to the board, or start a voice call and talk out loud. Your companion answers, says what they think about the game, and reacts when it ends. They do not comment on every move, so quiet stretches are normal.

Will my companion remember our games?

Yes. Each finished game is saved in your chat, and you can open it to step through the moves. Your companion can also save what mattered to their long-term memory and bring it up later, in chess or in another game. Memories stay on your computer.

Is the game timed? Can I choose my color?

There is no clock, so take as long as you like. Before each game you pick White, Black, or Random. During the game you can offer a draw or resign, and when it ends you can start a rematch.

Can I take back a move or ask for a hint?

No. There are no takebacks, hints, or engine evaluations, the same as playing a friend across a real board. You can draw arrows and circles on the board to plan, and you can ask your companion what they think, in character.

Can I play while my companion is in Minecraft?

Not at the same time with the same companion. If they are in a Minecraft session, Sei offers to disconnect them first. An unfinished chess game stays where you left it.

Is chess with Sei free?

You can start for free with no card. Chess uses the same weekly allowance as chat and calls on the hosted plans. If the allowance runs out during a game, your companion keeps playing their moves but stops talking until it refreshes. The app is open source, and you can also run it with your own API key or a local model.

Play a game

Download Sei, pick a companion, and choose Chess from Play together in your chat.