4.2.1

What's new in 4.2.1

This release replaces the evaluation network entirely.

GaiaNet-T1

More detailed threat features, and a larger network than before.

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Which file should I download?

File	Requires	Recommended for
gaiachess-nnue-znver5.exe	AMD Zen 5	Ryzen 9000 series
gaiachess-nnue-znver4.exe	AMD Zen 4	Ryzen 7000 series
gaiachess-nnue-znver3.exe	AMD Zen 3	Ryzen 5000 series
gaiachess-nnue-avx512.exe	AVX-512 (Intel Ice Lake+)	Intel 11th gen+
gaiachess-nnue-avx2.exe	AVX2 (Intel Haswell+, AMD Zen+)	Generic fallback for any modern CPU (2014+)
gaiachess-pesto.exe	Any x86-64 CPU	Older machines without AVX2 support

How to check: on Windows, open a command prompt and run wmic cpu get name. Then:

• AMD Ryzen 9000 (Zen 5) → nnue-znver5
• AMD Ryzen 7000 (Zen 4) → nnue-znver4
• AMD Ryzen 5000 (Zen 3) → nnue-znver3
• Intel 11th gen+ → nnue-avx512
• AMD Ryzen 1000–3000 (Zen–Zen 2) or Intel Haswell–10th gen → nnue-avx2
• Older CPUs (pre-2014, no AVX2) → pesto

If unsure, try nnue-avx2 first — it works on any CPU made after ~2014. If it
crashes on startup, fall back to pesto.

The NNUE versions are several hundred Elo stronger than PeSTO thanks to the
neural network evaluation, but require AVX2 for the SIMD inference.

Each executable is self-contained: the neural network and the 3+4-piece DTM
tablebases are embedded, so there is nothing else to download.

UCI Options

Option	Type	Default	Description
Hash	spin	16	Transposition table size in MB (1–1048576)
Threads	spin	1	Number of search threads (1–256)
EvalFile	string	<internal>	Path to a .nnue network file
Ponder	check	true	Enable pondering
MultiPV	spin	1	Number of principal variations (1–256)
Move Overhead	spin	100	Time buffer in ms for GUI/network lag (0–5000)
SyzygyPath	string	<empty>	Path to Syzygy tablebase files
NalimovPath	string	<empty>	Path to Nalimov tablebase files
OnlineTB	check	false	Query online tablebases when local ones are unavailable

License

Gaia is distributed free of charge. Gaia may not be distributed as part of any
software package, service or web site without prior written permission from the
authors.

© 2003–2026 Jean-François Romang

4.1.3

Bug fix: TB root move shuffle
When Syzygy tablebases were active at the root, the engine skipped sorting root moves by search score to preserve DTZ ordering. This caused it to mechanically repeat the first DTZ-ranked move even when it led to repetition draws in won positions.

Reported by Werner Schüle

4.1.2

Syzygy Tablebases :

• DTZ-optimal root probing: bestmove in tablebase positions (e.g. KBB vs K) is now chosen by optimal DTZ distance, fixing cases where the engine failed to make progress toward mate.

4.1.1

Search & Evaluation

• Insufficient material draw detection — KvK, KBvK, KNvK, KBBvK
• GHI bugfix — Fix KQ vs K draw by repetition caused by mate score + 50-move rule interaction

Windows Builds

• PeSTO (no NNUE) build for legacy CPUs — New gaiachess-pesto.exe for machines without AVX2 (pre-2014)
• Renamed executables — nnue-avx2, nnue-avx512, nnue-znver3, nnue-znver4, nnue-znver5 (was generic-*)
• See the README for which file to use on your CPU

4.1.0

First public release !