Tesla released Full Self-Driving (Supervised) v14.3.9 on 6 September 2026, inside firmware 2026.27.5. It is a Hardware 4 build for North America, covering Model S, Model 3, Model X, Model Y and Cybertruck. At the time of writing it sits at 0% of the tracked fleet with no cars logged — the same standing start v14.3.8 had two weeks ago.
The release notes are long. Most of them are not new.
What is genuinely new in 14.3.9
Read against the v14.3.8 notes, five things change.
- Automatic Collision Evasion gets its own heading. FSD (Supervised) can now activate during manual driving when a frontal collision is imminent and braking alone may not avoid it, or when the car detects inattention or an unintended disengagement. TeslAnt covered the feature when Tesla first described it on 3 September; 14.3.9 is the build that carries it.
- One model across three products. Actually Smart Summon, FSD and Robotaxi now run a unified model rather than separate stacks.
- Smart Summon tops out at 8 mph, up from its previous walking-pace limit.
- Intervention tracking and distance travelled appear in the interface, so the car reports how often you took over.
- Map-based parking options at a destination, plus reduced lane bias and tailgating, better recovery from temporary system degradations, and improved 3D geometry and traffic-sign recognition.
What is carried over from v14.3.8
This is the part that catches people out, because the wording is identical rather than merely similar:
| Bullet in the 14.3.9 notes | Also in 14.3.8 |
|---|---|
| Rewrote the AI compiler and runtime with MLIR, 20% faster reaction time | Yes, verbatim |
| Upgraded reinforcement learning training stage | Yes |
| Vision encoder for rare and low-visibility conditions | Yes |
| Traffic lights at complex intersections | Yes |
| Emergency vehicle and school bus response | Yes |
| Parking spot decisiveness | Yes |
| Small animal handling | Yes |
| Driver monitoring and eye-gaze tracking | Yes |
If you read the notes cold, 14.3.9 looks like a substantial neural-network release. It is not. The compiler rewrite and the 20% reaction-time figure were the headline of the previous build, and Tesla has simply reprinted them. The same thing happened at v14.3.7, whose notes were identical to v14.3.6.
Pothole avoidance is still listed as upcoming, which is where it was when Tesla said it was coming soon at the end of August.
What European cars are running instead
Nothing here reaches Europe. European FSD cars are on a different branch entirely: 2026.27.200, carrying FSD 14.2.2.6, which arrived on 1 September and is at about 1.2% of the fleet. That firmware is the one that shipped the EU recall remedy for pole side impact, and its FSD version is more than a point release behind North America's.
So a European owner reading about Automatic Collision Evasion is reading about a feature on a branch their car is not on, in a market where FSD (Supervised) is still only recognised in six member states.
Worth knowing
A 0% fleet figure on release day is normal for this branch and says nothing about quality. What it does mean is that nobody has driven enough kilometres on 14.3.9 for the usual pattern — a fix build following within a fortnight — to be ruled in or out yet.
Update: 2026-09-09
On 9 September 2026, NotATeslaApp published the first owner reports from v14.3.9. Testers describe faster decisions on lane changes and at intersections in Hurry mode, less delay between evaluating a manoeuvre and executing it, and destination parking that pulls closer to driveways instead of stopping short; highway behaviour is reported as well-centred over long distances. Two complaints survive from earlier builds: the car still misreads speed-limit drops approaching small towns, and it lingers in the left lane after passing unless prompted with the turn signal. Automatic Collision Evasion, the build's one genuinely new feature, has not been observed triggering in ordinary driving — testers are arranging closed-course tests to evaluate it safely.
Update: 2026-09-12
Tesla moved this build onto different firmware within two days of releasing it. FSD v14.3.9 now ships in 2026.27.6, not the 2026.27.5 named above, and Not a Tesla App carries official release notes for the newer firmware under the same FSD version number. The replacement matters because 2026.27.6 is also the build that carries v14.2 Lite to Hardware 3 cars: one firmware now serves both computers, with Hardware 4 cars getting v14.3.9 and Automatic Collision Evasion, and Hardware 3 cars getting v14.2 Lite without it. Tesla Oracle documented the switch on 12 September 2026. The release notes themselves did not change — the 2026.27.5 designation is simply superseded.