That is bad news. It's too clean looking and parallel to the headtube top face to be at all likely to be a random scratch. It looks like a defect with the headtube. Even if it were a scratch, it would be a deep one in one of the more highly stressed areas of the bike. It looks like something that should be resolved either via warranty or carbon repair.
That does not look good. It looks to be the very top of the head tube that is unsupported by the headset race on the inside.
Things to try:
- Give the area a good hard squeeze with your hand. No head tube should flex at all with mere hand pressure. If you can feel it deforming, immediately stop riding this frame.
- Try getting the bike's rider to sit on the bike while you stand in front with the front wheel between your legs. Get the rider to "push and pull" on the bars like they're riding but not pedalling. Again, hold your hand on this area and feel for deflection, distortion, and flex. If you feel any of that, again stop riding.
- Lastly, take a fine permanent marker and draw on the frame showing the exact end of the visible crack. If you check again periodically, and see that the crack has expanded, then immediately stop riding.
What are the risks? Imagine the crack propagates all the way around the head tube, so the top bearing race is not secured to the frame. The steering will be compromised - it may just go a little floppy allowing the rider to stop carefully, or it may wedge up and be uncontrollable and any turning effort simply throws the rider off sideways because they can't balance.
Rider's hands might let go of bars under a sudden shock too, resulting in a lack of control.
The wheels and transmission and saddle will be unaffected, but braking could be affected because the hand/lever relationship changed suddenly.
If the rider is going fast when it breaks, its more likely to be a fall compared to if the rider is waiting stopped at the lights.
However noone can pick when a part will break. Murphy says it will happen at the worst time possible.
Do please edit your results into the question. I would explore warranty/manufacturing defect options, and personally I would not ride the bike.