On August 4, during the opening of the FMS 2026 conference in California, SK Hynix, in collaboration with SanDisk, introduced the initial specifications for HBF, a new technology positioned as an intermediary layer between high-speed HBM memory and SSD storage.

Key technical specifications for HBF include:

  • Capacity of up to 512 GB (configured with 8 or 16 NAND chips);
  • Bandwidth ranging from approximately 0.4 TB/s to 3.0 TB/s;
  • Connection interface utilizing UCIe, an open standard that ensures compatibility with various manufacturers’ GPUs and CPUs.

https://www.youtube.com/watch?v=VMbPrcx2oIg&t=26s

The specifications have been released through the Open Compute Project, a community focused on data center technologies. This positions HBF as an industry-wide open standard rather than a proprietary solution.

Following the announcement of HBF, modern AI servers are likely to adopt a four-tier memory hierarchy:

  1. HBM — processes "hot" data directly in the computing core (highest speed, minimal capacity, extremely high cost).
  2. CXL — enhances traditional RAM by reducing latency to tens or hundreds of nanoseconds, while maintaining full compatibility with CPU/GPU.
  3. HBF — bridges the gap between RAM and SSD, offering speeds close to HBM through direct integration with the processor via the UCIe bus, but with higher capacity using cost-effective NAND architecture.
  4. NVMe SSD — used for storing "cold" data.

In LLM infrastructure, a significant challenge lies in managing vast contexts and model weights during computations (inference):

  • CXL handles data requiring instant access and frequent rewriting with ultra-low latency;
  • HBF is responsible for storing gigabyte-scale context caches and AI model weights that exceed the capacity and affordability limits of HBM and CXL.

The partnership between SK Hynix and SanDisk for HBF standardization commenced in August 2025. The consortium was launched in February 2026 and also includes Google and Tenstorrent.

Additionally, at the FMS 2026 exhibition, SK Hynix announced a demonstration of its 375-layer 4D NAND (V10), which is currently under development. The company claims that memory performance has increased by 2.5 times per watt of energy compared to the previous generation. Mass production of eSSD is scheduled for early next year.

According to Yahoo Finance, SK Hynix's shares have surged over 330% since the beginning of 2026, though they have lost nearly half their value since peaking in June.

Stock chart of SK Hynix since the beginning of 2026. Source: Yahoo Finance.

It is worth noting that in July, the Ashenbrenner fund divested a significant portion of its stock portfolio.