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CCERL-2P10-v2

CCERL-2P10-v2 is the second public Chinese Checkers Engine Rating List ruleset for this repository, superseding CCERL-2P10-v1 as of 2026-05-21. It is tied to the current C++ strict rule profile (CCZ-121-Strict-LG-v2) so benchmark games can be reproduced by the checked-in referee.

What changed from v1

A single rule was tightened: the anti-block terminal. Under v1, the terminal additionally required the winning player to have completely vacated their own home triangle (home_count[player] == 0). That gate let opponents force max_ply draws by stranding a single piece in their own home (which geometrically coincides with the winning player's goal-blocker territory). In extended evaluation we observed this exploit at scale: a deterministic rule bot produced 101 max-ply draws over 172 games against the champion, despite never winning a decisive game.

The v2 anti-block rule is the natural reading of "your goal is effectively full": if every cell of your goal triangle is occupied (by your own pieces plus opponent blockers) and at least one cell is yours, you win.

For full motivation, before/after Elo impact, and migration guidance, see docs/benchmark/CHANGELOG_2P10_V1_TO_V2.md.

Scope

  • Two players.
  • 10 pieces per player.
  • Standard 121-hole star board.
  • Side triangles are playable.
  • No captures.
  • Player 0 starts in the top home triangle and moves toward the bottom goal triangle.
  • Player 1 starts in the bottom home triangle and moves toward the top goal triangle.

Moves

On each turn, the side to move moves one own piece by either:

  • one adjacent step to an empty neighboring hole; or
  • a hop chain of one or more hops.

Each hop jumps over one occupied adjacent midpoint, occupied by either player, and lands on the empty hole directly beyond it. Hop chains may change direction after each landing. Jumped pieces are not captured. A hop chain may not revisit a landing hole inside the same move.

The referee stores each move as:

  • integer from cell id;
  • integer to cell id;
  • witness path, including the source, intermediate hop landings, and final destination.

Goal Locking

Goal locking is enabled. Once a piece lands in its own goal triangle, every later landing for that piece must remain inside that same goal triangle. This applies both across turns and within a single hop chain.

Terminal Results

The game ends immediately when one of these conditions is reached:

  • all_pieces_in_goal: a player has all 10 pieces in their own goal triangle.
  • equal_turn_goal_draw: both players have all 10 pieces in goal, or player 0 has just completed and player 1 has an immediate legal completing reply.
  • anti_block_goal_full (v2 — tightened): a player's goal triangle is effectively full: every goal hole is occupied by either that player or an opponent blocker, and at least one blocker is present. The v1 requirement that the winning player had vacated their own home triangle is removed.
  • repetition: the same player-to-move position hash occurs three times.
  • max_ply: the game reaches the configured maximum ply count.
  • no_legal_moves: the side to move has no legal move.

Draws score 0.5 for each engine. Wins score 1.0 for the winner and 0.0 for the loser.

Benchmark Defaults

The first CCERL-2P10-v2 benchmark uses:

  • engine profile: strict (resolves to CCZ-121-Strict-LG-v2);
  • champion: latest promoted JumpStar checkpoint (currently experiments/fresh_selfplay_alpha/champions/iter_063_*/model.ccpv);
  • MCTS simulations: 768;
  • move generator: bitboard;
  • inference backend: auto;
  • inference batch size: 64;
  • position schedule: benchmarks/ccerl-v1/positions/official_elo.jsonl;
  • opening diversification: 102 frozen opening exits sampled from mixed classical bot sources at 4, 8, 12, 16, and 24 plies;
  • clean-start floor: 26 explicit initial-board rows, roughly 20% of the 128 row schedule;
  • pairing: each row is played twice with colors swapped;
  • default max plies: 240.

The Elo scale is engine-only. It is not a human rating.

Reproducing v1 results

Pre-2026-05-21 benchmark artifacts were recorded under CCERL-2P10-v1. They remain reproducible by passing --rules strict-v1 to cczero match and related commands. See docs/benchmark/RULE_PROFILES.md for the full table of CLI rule names.