What is Queue-reactive model?

A queue-reactive model describes each best queue of a book as a birth–death process whose rates depend on the queue’s current size $q$: limit orders join its back at rate $\lambda^L(q)$, cancellations remove resting orders at rate $\lambda^C(q)$, market orders remove orders from its front at rate $\lambda^M(q)$. When a queue empties the price moves by one tick and new queues are drawn from a regeneration distribution.