The two computers
Tesla designs its own inference hardware and has shipped two generations that matter for FSD: HW3, introduced in 2019, and HW4, which Tesla also calls AI4, introduced from early 2023 depending on model. Both are capable of running FSD. They are not equally capable of running the newest software at full quality.
| HW3 (FSD Computer 1) | HW4 (AI4) | |
|---|---|---|
| Shipped from | 2019 | 2023, by model |
| Runs FSD (Supervised) | Yes, reduced build | Yes, full stack |
| Current software | v14 Lite generation | Full v14 generation |
| Camera hardware | Earlier sensors | Higher-resolution cameras |
| Retail upgrade to newer | Not offered | N/A |
HW3: supported, no longer cutting edge
HW3 is the computer that made FSD a mainstream product, and there are millions of cars with it. It still runs FSD, and for a long time it ran the same software as everything else. That changed in mid-2026, when Tesla began rolling a reduced build — reported as v14 Lite — to HW3 vehicles while keeping the full v14 stack on HW4.
The practical difference is not a switched-off feature list so much as quality and confidence: fewer of the hardest scenarios handled well, and more moments where the system hesitates or asks for help. For a highway commuter it is still useful. For someone expecting the best version of the product, the hardware matters.
Get the first month free
Scan the code with your phone, or open the referral and subscribe to FSD in the same session. The code is
michael496060.
HW4 (AI4): what the extra hardware buys you
- The full current software stack, including the v14 generation and its successors as they ship.
- Higher-resolution cameras, which matters most in low light, rain and at distance.
- More compute headroom, which is what lets Tesla keep adding to the stack rather than trimming it.
- A front bumper camera on newer builds, which improves close-in visibility for parking and low-speed manoeuvres.
If you are choosing between two used cars at similar prices and both are FSD-capable, the HW4 car is the one that will keep receiving the good software. That is a durability argument, not a performance one.
How to check what your car has
Do not rely on the model year alone, because Tesla has changed hardware mid-year and per model line.
- In the car Open Controls, then Software, then Additional Vehicle Information. The screen lists the autopilot/FSD computer generation.
- From the VIN A Tesla service centre or a VIN decoder can confirm the build configuration; for a used car, ask the seller for the Additional Vehicle Information screenshot.
- From the app The vehicle details in the Tesla app show the software version, which is a strong hint but not a hardware confirmation.
- Ask before you subscribe If you cannot confirm the hardware, do not start a subscription — the free month is worth more than a guess.
What this means when buying used
Two questions decide what you are actually buying: which computer is fitted, and whether FSD was purchased outright by a previous owner or only subscribed.
- A car with FSD purchased outright keeps the licence with the VIN, so the features stay after the sale.
- A car whose owner only subscribed loses those features when that subscription ends. You would need to subscribe yourself.
- HW3 cars are perfectly good cars, but the FSD experience is the reduced build and will stay that way without a hardware upgrade that Tesla does not currently sell.
- A used listing that says "FSD included" without saying purchased or subscribed is telling you half of the important thing.
The FSD transfer guide covers the ownership and resale questions in full.
Will HW3 get an upgrade?
Tesla has said it intends to keep HW3 cars supported, and it has run paid retrofit campaigns before — most notably the HW2.5 to HW3 upgrade for owners who had bought FSD. It has not offered a general retail path from HW3 to HW4, and there is no announced price or programme for one.
Treat an upgrade as possible but unconfirmed. If full-stack FSD matters to you and you are choosing a car now, buy the hardware that already has it rather than betting on a retrofit.
Do you need HW4 for the free month?
No. The referral credit applies to a new FSD subscription on any eligible vehicle, and HW3 cars are eligible. What you get for your free month depends on the hardware you already have, not on which code you used.
That makes the free month a fair test: it shows you the software your car will actually run, which is the only version you should be deciding about. The referral code guide has the sequence; is FSD worth it has the decision framework.
Questions people actually ask
Which Teslas have HW4?
Cars built from early 2023 onward, depending on model: Model S and Model X first, then Model 3 and Model Y during 2023. Because Tesla switched mid-year and per line, check the Additional Vehicle Information screen rather than trusting the model year.
Can HW3 be upgraded to HW4?
Tesla has not offered a retail HW3 to HW4 upgrade and has not announced a price or programme for one. It has run limited retrofit campaigns in the past, so it is possible in principle but should not be assumed when buying a car.
Does FSD still work on HW3 in 2026?
Yes, but on a reduced software build. Since mid-2026 HW3 vehicles have received the v14 Lite generation while HW4 cars get the full stack, so the experience is meaningfully different even though both are sold as FSD (Supervised).
How do I know if my Tesla has FSD hardware?
Open Controls, then Software, then Additional Vehicle Information in the car. It lists the autopilot/FSD computer generation. When buying privately, ask for a photo of that screen before you agree a price.