Comma.ai's Chestnut eGPU Dock Ships With Auditable, Open-Source Bridge Firmware

George Hotz’s comma.ai has released Chestnut, a PCIe Gen4 x4-to-USB4 eGPU dock whose controller firmware is published openly on GitHub under the tinygrad organization. It comes in two flavors: a $249 bare dock (bring your own card) and a $799 ‘ready to drive’ bundle that includes an AMD Radeon RX 9060 8GB plus cabling and mounting hardware, both with a 30-day trial and one-year warranty. The dock was built for a narrow purpose — letting a comma four driving computer hang a real desktop GPU off itself to escape openpilot’s roughly 10 W on-device power ceiling, pushing the budget to about 100 W and, per comma, into the same compute class as Tesla’s HW4. That headroom feeds a new 1B-parameter driving model in openpilot 0.11.2, which the company pegs at 30x the parameters and 100x the FLOPs of its current on-device model.

The broader interest lies outside cars. Chestnut is one of the first eGPU docks whose bridge silicon isn’t a sealed black box. The repo contains C firmware for ASMedia’s ASM2464PD, the USB4/Thunderbolt-to-NVMe bridge controller found in many USB4 NVMe enclosures — meaning the debug and control layer that retail enclosures have always kept locked is finally readable and reflashable. The documented throughput on that control plane is modest (a TLP read/write path around 3.6 MB/s write and 1.8 MB/s read, plus a ~700 MB/s DMA route into the chip’s 512 KB SRAM), but these are diagnostic and control figures, not gaming numbers.

Two caveats temper the enthusiasm. A Gen4 x4 link over USB4 is a narrow pipe compared to the x16 slot a card like the RX 9060 expects, so this is not a route to full desktop performance. And an open firmware repo isn’t a supported consumer product — comma is targeting people running larger driving models (and, unsurprisingly, tinygrad workloads), not Linux users seeking a better Razer Core. Even so, a $249 dock you can actually audit and reflash is a notably more open object than the eGPU market has offered to date.