On August 4th at the opening of the FMS 2026 conference in California, SK Hynix, together with SanDisk, published the first specifications for HBF—a technology aiming to serve as an intermediate layer between high-speed HBM memory and SSD storage.
Key technical characteristics of HBF:
- Capacity — up to 512 GB (in 8- and 16-die NAND stack configurations);
- Bandwidth — from ~0.4 TB/s to 3.0 TB/s;
- Connection interface — UCIe, an open standard ensuring compatibility with GPUs and CPUs from different manufacturers.
The specifications are open-sourced via the Open Compute Project—a community for data center technologies. This positions HBF as an industry-wide open standard rather than a proprietary development.
Following the announcement of HBF, modern AI servers will likely have a four-tier memory hierarchy:
- HBM — processes "hot" data directly in the compute core (highest speed, minimal capacity, extremely high cost).
- CXL — accelerates traditional RAM with latencies on the order of tens to hundreds of nanoseconds, while maintaining full compatibility with CPUs/GPUs.
- HBF — fills the gap between RAM and SSDs. By integrating via the UCIe bus directly with the processor, these devices will provide speeds close to HBM but with large capacity based on inexpensive NAND architecture.
- NVMe SSDs — store "cold" data.
In LLM infrastructure, a key challenge is storing the vast context and model weights during computation (inference):
- CXL handles data requiring instant access and frequent rewriting with ultra-minimal latency;
- HBF takes on storing gigabytes of context caches and AI model weights that could not fit into HBM and CXL due to their high cost and capacity limitations.
Silicon Curtain
The partnership between SK Hynix and SanDisk to standardize HBF began in August 2025. The consortium was launched in February 2026 and also includes Google and Tenstorrent.
Also at the FMS 2026 exhibition booth, SK Hynix announced a demonstration of 375-layer 4D NAND (V10), which is under development. According to the company, the memory's performance has increased 2.5 times per watt of energy consumed compared to the previous generation. Mass production of eSSDs is planned for early next year.
According to Yahoo Finance, SK Hynix shares have risen more than 330% since the beginning of 2026, but have lost about half their value since reaching a peak in June.
Recall that in July, the Ashenbrenner fund lost the majority of its stock portfolio.
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