Function prefetch_k 

pub fn prefetch_k() -> usize

ATLAS_DS41_PREFETCH_K (default 0 = off), read once: how many of the next layer’s predicted experts to start reading while this layer computes (needs ATLAS_DS41_READER_POOL=1). Off by default: on the 09-19 standard the predictor’s router launch (2.7 ms a token) and the wasted reads on the shared disk cost more than the caught misses saved (K=4: 12.50/16.67, K=6: 13.63/16.39, against 14.20/17.73 without).