Arena
Play chess against frontier AI models. Enter your OpenRouter API key, pick a model, and start a game. The model sees the board as FEN + legal moves — no vision.
Stored locally. Never sent to our servers.
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How it works
- • You play White, the AI plays Black
- • AI receives FEN + legal moves — no board image
- • Calls are made directly from your browser via OpenRouter
- • Temperature: 0 for deterministic play
- • Promotions auto-promote to queen
Model: Claude Sonnet 4.5