xHC (Expanded Hyper-Connections) breaks through the N=4 engineering bottleneck that HC/mHC had been stuck on, expanding the residual stream to N=16 via "temporal feature enhancement + sparse residual architecture". On 18B/28B MoE, downstream performance averages +4.0 points over mHC; at the same loss, vanilla/mHC need 1.50× / 1.19× compute. The companion xHC-Flash compresses per-sub-layer memory traffic from 73.5C to 40C, approaching the mHC N=4 level of 34C.