f_gate(x, y) = f(x) * y
for some f. In your case b is a constant hyperparameter though, e.g. f_gate(x) = 4 * tanh(x / 4) * sigmoid(x)
So where's the gate?Figure 2 (p3) has the architecture diagram for K3 (which is the same one on the Kimi K3 blog post https://www.kimi.com/blog/kimi-k3). AFAICT, that diagram along with section 2.3 should answer your question.
Note: I'm not familiar with LLM/NN architecture to answer it more precisely than that; I only have a surface level understanding from watching various YouTube channels like 3B1B and Welch Labs on the subject.