Exhaustive search over 387,328,512 configurations proved magnitude 10 is optimal for XOR3. This flat 2-layer architecture beats the cascade approach (magnitude 14) by 29%.
Architecture
Neurons
Params
Magnitude
Cascade (2×XOR)
6
18
14
Flat 3-hidden
4
16
10
Architecture
a ──┐
b ──┼──► [h1] ──┐
c ──┘ [h2] ──┼──► [out] ──► XOR3(a,b,c)
[h3] ──┘
Single hidden layer with 3 neurons, all biases = 0.
Solutions
18 solutions exist at magnitude 10, related by input permutation and neuron reordering symmetry.