Claude Sonnet 5.5
Anthropic · released 2026-09-28 · route claude-sonnet-5-5 · Model profile
Opening gap: +193 (95%: -43 to +429). The interval includes zero, so we can't yet say whether it performs differently across the variants.
Standard
- Rating
- 1,28795%: 1,114 to 1,460
- Record
- 16 won, 0 drawn, 8 lost of 24
- Accuracy (open positions)
- 84.7
- Accuracy (all moves)
- 88.0
- Average centipawn loss
- 66
- Blunders / mistakes / inaccuracies per 100 moves
- 7.3 / 3.0 / 7.7
- Matched Stockfish's first choice
- 36%
- In Stockfish's top three
- 62%
- Legal on the first try
- 94.3%
- Illegal / invalid
- 47 of 844 answers
- Forfeits
- 0
- Adjudicated games
- 20
- API-equivalent cost per game
- $0.404
- API-equivalent cost per move
- $0.012
- Seconds per move
- 9.2
- Model minutes per game
- 5.1
- Tokens per move (in / out)
- 1,052 / 796
- Reasoning tokens per move
- 759
- Aborted on our side (not counted)
- 1
By phase
| Phase | Moves | Accuracy | Centipawn loss | Blunders /100 | Engine match |
|---|---|---|---|---|---|
| Opening | 240 | 91.7 | 31 | 4.2 | 47% |
| Middlegame | 349 | 76.4 | 96 | 12.9 | 30% |
| Endgame | 208 | 88.0 | 56 | 1.4 | 33% |
Chess960
- Rating
- 1,09495%: 933 to 1,254
- Record
- 11 won, 1 drawn, 12 lost of 24
- Accuracy (open positions)
- 81.4
- Accuracy (all moves)
- 86.2
- Average centipawn loss
- 79
- Blunders / mistakes / inaccuracies per 100 moves
- 7.1 / 4.8 / 11.2
- Matched Stockfish's first choice
- 28%
- In Stockfish's top three
- 50%
- Legal on the first try
- 92.3%
- Illegal / invalid
- 73 of 944 answers
- Forfeits
- 0
- Adjudicated games
- 17
- API-equivalent cost per game
- $0.531
- API-equivalent cost per move
- $0.015
- Seconds per move
- 10.8
- Model minutes per game
- 6.5
- Tokens per move (in / out)
- 1,163 / 999
- Reasoning tokens per move
- 955
- Aborted on our side (not counted)
- 0
By phase
| Phase | Moves | Accuracy | Centipawn loss | Blunders /100 | Engine match |
|---|---|---|---|---|---|
| Opening | 240 | 81.2 | 70 | 8.8 | 22% |
| Middlegame | 392 | 81.3 | 87 | 8.9 | 31% |
| Endgame | 239 | 82.7 | 76 | 2.5 | 28% |
Games
Standard as blackWon vs Skill 0, 10% random moves64 plies · adjudicated: decisive advantage · $0.400Chess960 as blackWon vs Skill 0, 25% random moves50 plies · adjudicated: decisive advantage · $0.339Standard as whiteLost vs Stockfish Skill 287 plies · adjudicated: decisive advantage · $0.577Chess960 as whiteWon vs Stockfish Skill 077 plies · adjudicated: decisive advantage · $0.528Standard as blackWon vs Stockfish 132062 plies · adjudicated: decisive advantage · $0.396Chess960 as blackLost vs Skill 0, 10% random moves51 plies · checkmate · $0.284Standard as whiteWon vs Skill 0, 10% random moves75 plies · adjudicated: decisive advantage · $0.422Chess960 as whiteLost vs Skill 0, 10% random moves95 plies · adjudicated: decisive advantage · $0.741Standard as blackWon vs Stockfish Skill 040 plies · adjudicated: decisive advantage · $0.204Chess960 as blackLost vs Stockfish 1320126 plies · adjudicated: decisive advantage · $1.04Standard as whiteWon vs Skill 0, 10% random moves73 plies · adjudicated: decisive advantage · $0.364Chess960 as whiteLost vs Skill 0, 10% random moves123 plies · adjudicated: decisive advantage · $0.898Standard as blackWon vs Skill 0, 25% random moves56 plies · checkmate · $0.268Chess960 as blackWon vs Skill 0, 25% random moves94 plies · adjudicated: decisive advantage · $0.652Standard as whiteLost vs Stockfish 150087 plies · adjudicated: decisive advantage · $0.493Chess960 as whiteLost vs Stockfish 150075 plies · adjudicated: decisive advantage · $0.544Standard as blackLost vs Stockfish 1320128 plies · adjudicated: decisive advantage · $0.896Chess960 as blackWon vs Skill 0, 10% random moves64 plies · adjudicated: decisive advantage · $0.445Standard as whiteWon vs Skill 0, 10% random moves33 plies · checkmate · $0.215Chess960 as whiteWon vs Skill 0, 10% random moves67 plies · adjudicated: decisive advantage · $0.425Standard as blackLost vs Stockfish Skill 098 plies · adjudicated: decisive advantage · $0.672Chess960 as blackLost vs Stockfish 132055 plies · checkmate · $0.452Standard as whiteWon vs Skill 0, 10% random moves53 plies · adjudicated: decisive advantage · $0.276Chess960 as whiteWon vs Skill 0, 10% random moves57 plies · adjudicated: decisive advantage · $0.374Standard as blackLost vs Skill 0, 10% random moves136 plies · adjudicated: decisive advantage · $0.890Chess960 as blackWon vs Skill 0, 25% random moves60 plies · adjudicated: decisive advantage · $0.516Standard as whiteLost vs Stockfish Skill 236 plies · checkmate · $0.212Chess960 as whiteLost vs Stockfish Skill 0107 plies · adjudicated: decisive advantage · $0.958Standard as blackWon vs Stockfish 132060 plies · adjudicated: decisive advantage · $0.354Chess960 as blackLost vs Skill 0, 10% random moves86 plies · adjudicated: decisive advantage · $0.578Standard as whiteWon vs Skill 0, 10% random moves41 plies · adjudicated: decisive advantage · $0.221Chess960 as whiteLost vs Skill 0, 10% random moves38 plies · checkmate · $0.204Standard as blackWon vs Stockfish 132076 plies · adjudicated: decisive advantage · $0.411Chess960 as blackLost vs Stockfish Skill 069 plies · checkmate · $0.600Standard as whiteWon vs Skill 0, 10% random moves69 plies · adjudicated: decisive advantage · $0.369Chess960 as whiteWon vs Skill 0, 10% random moves55 plies · adjudicated: decisive advantage · $0.403Standard as blackWon vs Skill 0, 25% random moves34 plies · adjudicated: decisive advantage · $0.208Chess960 as blackWon vs Skill 0, 25% random moves54 plies · adjudicated: decisive advantage · $0.333Standard as whiteWon vs Skill 0, 10% random moves109 plies · adjudicated: decisive advantage · $0.758Chess960 as whiteLost vs Stockfish 1500121 plies · adjudicated: decisive advantage · $0.774Standard as blackWon vs Skill 0, 25% random moves28 plies · adjudicated: decisive advantage · $0.127Chess960 as blackWon vs Skill 0, 10% random moves64 plies · checkmate · $0.530Standard as whiteLost vs Skill 0, 25% random moves59 plies · adjudicated: decisive advantage · $0.557Chess960 as whiteDrew vs Skill 0, 10% random moves63 plies · threefold repetition · $0.515Standard as blackWon vs Skill 0, 25% random moves52 plies · adjudicated: decisive advantage · $0.278Chess960 as blackLost vs Stockfish Skill 050 plies · adjudicated: decisive advantage · $0.442Standard as whiteLost vs Skill 0, 25% random moves28 plies · checkmate · $0.125Chess960 as whiteWon vs Skill 0, 25% random moves33 plies · checkmate · $0.175