If you’ve been keeping an eye on the comma ecosystem, you already know the biggest limiting factor for openpilot has never really been the algorithms — it’s been the hardware doing the thinking in real time. Comma four is a capable little box, but it was never going to keep pace with the size of driving models comma wants to ship long term. That’s exactly the gap comma’s new Chestnut release is built to close.
What Chestnut Actually Is
Chestnut is a compute upgrade for comma four that lets the device offload inference to a real desktop-class GPU instead of relying solely on its onboard chip. Practically, that means pairing your comma four with an AMD Radeon RX 9060 (8GB) GPU, connected over a USB-to-PCIe adapter, mounted discreetly in the passenger footwell or under a seat.
Camera processing and driver monitoring still run on comma four itself — Chestnut isn’t replacing the device, it’s giving it a much bigger brain to hand the heavy lifting to. And if the GPU isn’t connected or something goes wrong, the car falls back gracefully to the smaller on-device model, so you’re never left without a functioning system.
Why It Matters: The Model Behind It
Hardware upgrades are only as interesting as what they unlock, and this one unlocks a lot. Chestnut launches alongside a new “chestnut-class” driving model — roughly 1 billion parameters, about 30x larger than the models that have been running on-device up to now, with around 100x more computational operations under the hood. For context, comma says the compute Chestnut provides is comparable to what you’d find in a Tesla HW4 setup.
Bigger isn’t automatically better in isolation, but comma’s fleet is logging nearly a million minutes of driving data every day, and that’s the kind of training volume that actually benefits from a much larger model architecture. This is comma testing how far openpilot can go once it’s no longer compute-constrained.
Price and Availability
Comma is offering two ways in:
- Chestnut (ready-to-drive kit) — $799, includes the GPU, adapter, cables, and mounting hardware
- Tiny Chestnut (GPU-only) — $249, for anyone who wants to source or reuse the rest of the setup themselves
Both options ship with comma’s standard 30-day money-back trial and a one-year warranty, so it’s a low-risk way to try the bigger model without committing long term.
Who Should Actually Buy This
Worth being clear-eyed here: Chestnut is currently supported on comma four only — comma 3X and comma three aren’t part of this release. And even on comma four, comma is upfront that a larger model means “more computing room,” not a guarantee of better performance on every route, in every car, or in every driving situation. This also isn’t a navigation upgrade — it doesn’t add new routing or map features, it’s purely about giving the driving model more headroom to work with.
If you’re happy with how openpilot drives today, you don’t need this. Chestnut is for the segment of the community that wants to be on the leading edge of comma’s largest model and is comfortable being part of that experiment.
Watch the Full Breakdown
I put together a full video walking through the Chestnut release, what’s actually in the box, and my first impressions after getting one running — check it out here: Chestnut Release Walkthrough
Let me know in the comments if you’ve picked one up yet, and what you’re seeing on your own comma four.