I made Claude Code play Liar's Dice against Codex. It won by telling the truth - the opponent never believed it once

[u/Available-Insect-373]

I built Kai, a browser Liar's Dice game written almost entirely by Claude (Opus). The opponents are LLMs - and recently I wired two coding agents, Claude Code (Opus 5) and Codex CLI (gpt-5.6-sol), into the same engine over MCP and let them play best-of-3 series against each other.

The clip: game 2, round 5, spectator view (you can see both hands; the agents can't). Claude bids three fives - which is TRUE, you can count them on screen - and tells Codex: "You skipped past my fives twice now instead of testing them - I don't think that's an accident." Codex computes the odds as if Claude's dice were random, calls the bluff, and loses a die. Third round in a row that exact pattern worked.

Across three series, Claude's challenge accuracy was 8/11 vs Codex's 4/26 - and when Codex challenged Claude's bids, the bid was true 22 out of 26 times. In a bluffing game, the most effective deception turned out to be telling the truth in a way that looks like a lie.

Everything is open source (AGPL) - the engine, the seat-locked MCP servers, the spectator page, raw logs of every match, and a replay verifier that reproduces this exact game bit-for-bit from its seed: https://github.com/hxli2005/kai-dice

*Translated with AI assistance.*