Blizzard v0.5

+53 Elo over 0.4. In a 100-game match Blizzard 0.5 scored +40 =35 −25 (57.5%), with a 95% interval
of −2 to +110 Elo, at 0.1 s per move with book openings, each opening played with both colors.
Against Stockfish 2800 it scores 65%, and against Stockfish 3000 30%.

What's new

Twice the neurons. The network is now 3072 → 2×256 → 1, with the same king-aware inputs as before.
Thanks to the WebAssembly SIMD code from 0.4, it is only about 5% slower than the 0.4 network.

More and better training data. The network was pretrained on 12.1 million positions with
Stockfish 19's static evaluation, then fine-tuned on 11.4 million positions scored by a short search
(1000 nodes each): 7.8 million by Stockfish 19 and 3.6 million new ones by the full Stockfish 16, whose
larger network judges positions more accurately. On 30,000 positions it never saw in training, its error
is 7% lower than that of the 0.4 network.

Tested and left out. ProbCut, history-based pruning, double and negative singular extensions, and
scaling the evaluation toward a draw as the fifty-move rule approaches lost 16 to 32 Elo against 0.4.
A second network layer (2×256 → 16 → 1) was 1.3% more accurate but 17% slower, and lost 83 Elo to the same
network without it. Another 3.9 million positions gave nothing measurable. The search is the same as in 0.4,
about 2% faster.

A new website. Black and white throughout. The first screen is a snowstorm with the word Blizzard; as you
scroll, the word scatters into snow and the snow gathers into the logo. Versions open to show what changed,
and comparisons have their own Compare tab. The play page is black and white too; only the move ratings
keep their colors.

Strength

Match	Games	Score	Elo difference (95% interval)
0.5 vs 0.4	100	57.5%	+53 (−2 to +110)
0.5 vs Stockfish 2800	40	65% (0.4 scored 61%)	+108 (+17 to +216)
0.5 vs Stockfish 3000	40	30% (0.4 scored 26%)	−147 (−250 to −64)

Stockfish 19 here is the single-threaded browser build, limited with UCI_Elo, at 0.2 s per move.
These are not FIDE or CCRL ratings; they compare Blizzard versions under the same conditions.

Downloads

File	For	SHA-256
blizzard-0.5-windows.zip	Windows 10/11, 64-bit, nothing to install	ad351a4ca34c8170819b67e45e12fd0f11fceccf5e1e196dd48ba309163106ca
blizzard-0.5-universal.zip	macOS, Linux and others, needs Node.js 18+	f789c07281d8ddaaa5b7225f4859583145d896fcca4ca31c0d44ee47a23c3d2d

Unpack, then add blizzard.exe (or node blizzard-uci.js) to Arena, Cute Chess, En Croissant or any
other UCI program. Play it in the browser at sacon1s.github.io/blizzard.

Upgrading from 0.4

• Replace the old files. UCI options are unchanged.
• UseNNUE false still switches to the hand-written evaluation.
• The engine still loads the 0.2, 0.3 and 0.4 networks.
• blizzard.exe is not code-signed: if SmartScreen warns, click More info, then Run anyway.