Who this is for
comma four owners who want the largest models and have room in the passenger footwell.
comma four
comma.aiHardware and wiringSome effort
Chestnut: comma's external GPU for comma four
Chestnut lets a comma four run comma's biggest driving models; the ready-to-drive kit includes the GPU and car cables.
You need
- A comma four
- The ready-to-drive kit, or the dock plus your own GPU and power supply
- A 12 V power point in the car
In plain words
Why this guide matters
Chestnut is comma's plug-in GPU box that gives a comma four far more computing power for openpilot's largest driving models. You can buy the dock alone or a ready-to-drive kit with a graphics card; check comma's page for current prices. You get the same hardware comma uses for its biggest models, without buying a new device.
The short version
What the full guide walks you through
Choose the dock-only or ready-to-drive kit.
Fit the GPU to the dock with the standoffs.
Mount it in the footwell or under the passenger seat.
Connect car power and the USB cable to the comma four.
Let openpilot load the bigger model at start-up.
Before you start
- comma four only; older devices are not supported by comma.
- Check the current price on comma's page.
The full written guide belongs to comma.ai. Checked on September 10, 2026.
Quick answers
Questions people ask
Does chestnut work with a comma 3X?
No; comma sells and supports chestnut for the comma four only. StarPilot claims support on older devices, but comma does not.
Where does chestnut go in the car?
In the passenger footwell or under the passenger seat, held with the included strips. It needs airflow and a 12 V power point.
Do I need chestnut to use openpilot?
No; the comma four runs the normal driving model on its own. Chestnut only matters if you want the biggest chestnut-class models.
Related
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All community guidesNot sure this is your path?
Check your exact car first, then choose software and hardware.
Photos: comma.ai. Guide content belongs to comma.ai. CommaGuide is an independent guide and is not affiliated with comma.ai or comma.ai.
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