Does tuning with ATLAS affect my Subaru warranty?

Yes, and the platform is irrelevant to the answer. This is worth stating plainly because ATLAS being free and open-source sometimes creates an impression that it is somehow less visible. It is not. Any software that writes to the ECU leaves the same evidence. Modern Subaru ECUs retain a record that reprogramming occurred, and a dealer with the right tools can see that regardless of which map is currently loaded or which software wrote it. Flashing back to stock removes the map; it does not remove the history. So the warranty position of an ATLAS-tuned car is the same as an Accessport-tuned car. Choosing one over the other changes nothing here. **What that actually means in practice.** A tune does not automatically void your entire warranty - that is not how it works. What it does is give the manufacturer grounds to decline a claim they can connect to the modification. A powertrain claim on a tuned car is a conversation you may not win. An unrelated claim, on infotainment or trim or suspension, is far less likely to be affected. The risk therefore concentrates exactly where repairs are most expensive, which is why this matters more than the paperwork suggests. **Sensible practices regardless of platform.** Save your factory file before your first flash, so returning to stock is always available. Return to stock before dealer visits. Keep factory hardware you have removed, because a stock map on a car with an obvious aftermarket J-pipe is not a convincing combination. And keep records of your own maintenance, because a well-documented car is a stronger position in any dispute. **Be honest with yourself about the tier.** A Stage 1 map on an otherwise stock car, flashed back before service, is a modest and manageable risk. A flex fuel system, a J-pipe or an upgraded turbo cannot be flashed away and are unambiguous signals the car has been modified. That is not a reason to avoid them - it is a reason to know where you stand before you fit them rather than afterward.