# AI defeats top Stratego champion in 2025 exhibition

> The Ataraxos system beat world‑record holder Johan Niemeijer, showing AI can handle games with hidden information.

Oossa · 2026-10-01 · https://oossa.com/en/ai-defeats-top-stratego-champion-in-2025-exhibition

In an exhibition match at the 2025 Stratego World Championship, a new AI called Ataraxos won 38 of 40 games against tournament players and later beat Johan Niemeijer, the most decorated Stratego player ever. Niemeijer, who has four world titles and spent more than 600 weeks at the top of the rankings, lost the three‑week series with a win rate of about 85 percent. The matches were streamed online, and the AI’s style was described as hard to read and willing to take risky bluffs.

## How Ataraxos pulled off the win

Ataraxos learned only by playing against itself, using a belief network to guess the opponent’s hidden pieces before each move. The researchers forced the AI to vary its opening setups early on, a technique called regularization, which kept it from settling into a predictable pattern. Training took one week on 16 Nvidia H100 GPUs and four additional days on four GPUs, costing under $8,000 at 2025 prices—about 1/500th of the compute DeepMind spent on its earlier DeepNash system.

## The facts

- Johan Niemeijer has four world championships, 15 Dutch titles and over 600 weeks at rank 1.
- Ataraxos beat 38 of 40 tournament players at the 2025 World Championship exhibition.
- In a three‑week series, Ataraxos defeated Niemeijer with an 85 percent win rate (draws counted as half a win).
- Training used 16 Nvidia H100 GPUs for one week plus four days on four GPUs, costing less than $8,000 in 2025.
- DeepNash needed 1,024 TPU nodes for 2–3 months, estimated at $3 million–$4.5 million in 2025.

## Why it matters

For regular board‑game fans, the result shows that AI can now handle games where you can’t see all the pieces, ending one of the last areas where humans were clearly better. It also hints that similar AI techniques could be applied to real‑world problems with hidden information, such as finance or negotiations, though the paper notes the current method doesn’t improve simply by adding more compute.

## Sources & references

1. [AI beats Stratego's greatest player, ending one of the last human strongholds in board games](https://the-decoder.com/ai-beats-strategos-greatest-player-ending-one-of-the-last-human-strongholds-in-board-games/) – The Decoder, 2026-10-01
2. [AI finally beat the best Stratego player in history—and did it on a budget](https://arstechnica.com/science/2026/10/ai-finally-beat-the-best-stratego-player-in-history-and-did-it-on-a-budget/) – Ars Technica, 2026-10-01

Last updated: 2026-10-01