A dramatic improvement over 14.3.8 for left-lane behavior, with an apparent overcorrection toward the right lane, unexplained right signals by late September, and several situations where an attentive driver needs to step in.
Researching 14.3.9 before deciding on FSD? If you already own a Tesla and have not had FSD in the past year, you may be able to try it free for a month on your own roads.
What got better (first impression, September 13)
- No more left-lane camping. Our biggest 14.3.8 frustration was the car parking itself in the passing lane. That stopped on 14.3.9.
- Quicker, more agile turns. The car commits to turns more naturally. It no longer feels like everyone behind us is waiting for it to decide.
- Calmer overall. We only had 14.3.8 briefly, but long enough to notice repeated lane-choice and timing frustrations. 14.3.9 immediately felt easier to live with.
What went wrong (follow-up, September 23)
| Behavior | What we saw |
|---|---|
| Exit-lane timing | Too early Moved into the far-right lane two to three miles before an exit and stayed behind much slower traffic |
| Right-turn lanes | Take over Resisted a dedicated right-turn lane, then appeared to try the turn from the straight-through lane |
| Braking | Jitters Occasionally jittered while braking without an obvious reason |
| Right signal | Unexplained Late September: signaled right three times on I-75 without changing lanes |
The right-turn-lane behavior is the serious one. It is a situation where I would take over before the turn rather than wait to see what FSD does. I do not know what triggered the braking jitters, so I am not calling them a specific braking-system fault.
Late September: better timing, unexplained signals (September 28)
By late September, 14.3.9 seemed less eager to move into the far-right lane miles before an exit. That was welcome after our mid-September drives, but too early to call fixed.
On I-75, the car activated its right turn signal three times without moving into the right lane. Another vehicle was in that lane each time. The latest happened on the afternoon of September 27 while we were driving south, roughly two and a half to three miles from our exit. From the driver's seat, I could not see a reason to signal then.
I do not know why the system signaled or whether it was preparing a lane change it could not complete. The car stayed in its lane; this is not a report of a collision or an unintended lane departure. I documented it because unexpected signaling can confuse nearby drivers.
Correction, October 31: we originally logged these late-September drives as 14.3.10. Our car actually went from 14.3.9 directly to 14.3.12. Unnecessary right-lane signaling came back late in our time on 14.3.12 and appears fixed on 14.3.13 so far.
Stop signs and speed
Stop signs: the car comes to a complete stop, which is right, but can then wait a few seconds longer than feels natural. Pressing the accelerator can prompt it, but only after I have personally confirmed the intersection is clear and proceeding is safe and legal.
Standard mode speed: in a posted 35 mph zone, the car crept toward 45 and stopped climbing there. Better than before, but I want Standard to stay within about five mph of the limit. That improved noticeably on 14.3.13.
What the 14.3.9 release notes say
The published notes for 14.3.8 (software 2026.26.6.5) and 14.3.9 (software 2026.27.6) list the same major FSD changes, summarized:
- Upgraded reinforcement learning and a stronger vision encoder
- Broader traffic-sign understanding
- A rewritten AI compiler and runtime described as reacting 20% faster
- Mitigations for unnecessary lane biasing and minor tailgating
- Improvements for parking, emergency vehicles, school buses, complex traffic lights, unusual objects, temporary system degradation and driver monitoring
- Pothole avoidance listed under upcoming improvements
Because the 14.3.8 and 14.3.9 notes are nearly identical, I am not claiming Tesla documented a specific left-lane or turning fix between them. The difference above is what we actually felt.
Automatic Collision Evasion
The 2026.27.6 notes describe Automatic Collision Evasion, which can activate FSD (Supervised) during manual driving if the system detects the driver is not sufficiently attentive or FSD may have been unintentionally disengaged. We have not triggered it. It is an extra safety layer, not a promise to avoid every collision. Do not test it.
What came next: 14.3.12, then 14.3.13, or see the full version history.
Questions about FSD 14.3.9
Is Tesla FSD 14.3.9 better than 14.3.8?
In our Model 3, the initial difference was dramatic: 14.3.9 stopped camping in the left lane and many turns felt quicker. Later drives exposed early moves into the exit lane, difficulty with some right-turn lanes and occasional braking jitters.
What problems does FSD 14.3.9 have?
On our drives it sometimes entered the far-right lane two to three miles before an exit, resisted a dedicated right-turn lane while appearing to turn from the straight-through lane, and occasionally jittered while braking. By late September it also signaled right three times on I-75 without changing lanes.
What version came after FSD 14.3.9?
Our car went from 14.3.9 directly to 14.3.12; we never had 14.3.10. Read the 14.3.12 review.
What software version includes FSD 14.3.9?
Our car ran FSD (Supervised) 14.3.9 on software 2026.27.6.
Can I try FSD for free?
If you already own or lease an eligible Tesla and have not had an FSD trial or paid subscription in the past 12 months, Tesla's FSD referral program may give you a one-month trial in the Tesla app. See how it works.
Supervised means supervised. FSD (Supervised) requires an attentive driver ready to take control and does not make the vehicle autonomous. These are dated observations from one Model 3 on our own routes; behavior varies by vehicle, hardware, build, location and conditions.