SK Hynix leads HBM4 yield at 60%, expands DRAM supply

SK Hynix pushing HBM4 yield past 60% is not a process milestone—it is a repricing of capacity allocation power. Once 12-hi hybrid bonding clears the break-even threshold, Hynix gains the rare elasticity to simultaneously fulfill AI accelerator HBM commitments and server DRAM long-term agreements. In the HBM3E era, only Samsung could force that through sheer wafer volume. The technical ripple is structural: HBM4's dedicated logic base die locks additional TSMC 5nm capacity into the HBM ecosystem, shifting the CoWoS-L bottleneck from stacking to base-die and TSV co-yield. For NVIDIA Rubin and AMD MI400, 60% signals volume ramp by Q4 2026, with true scale in Q1 2027. Competitively, Samsung remains stuck in customer qualification; Micron trails by roughly a quarter. Hynix's DRAM expansion will compress 2027 commodity DRAM pricing, forcing Samsung into a defensive HBM4 price cut plus DRAM output cut—but AI customer stickiness, once shifted, is irreversible. Twelve-to-twenty-four-month tail: every 10-point yield gain frees approximately 15% of DRAM wafer capacity. By mid-2027, if yield hits 75%, server DRAM faces structural oversupply while Hynix's yield moat converts directly into pricing power. That is the real industry reset.