I voted other: Alien attack
Bear in mind, the OP said "Extinction".
Nuclear war would probably take out 80-90%
AI, we are not to the point of making robots yet that could turn on us, so at best they could pull off nuclear war, which goes back to 80-90%.
Virus is possible, but Covid kinda proved that we can overcome these. Worst case, I'm thinking about 50%.
Asteroid is not likely as we are already tracking most of the planet-killers and most have their paths projected for the next 100 years already. Of the few that could potentially be a threat, I don't think we are that far away from technology capable of fixing the problem. (Bear in mind, outside of a complete "Holy crap, it's coming right for us" kind of asteroid that comes from outside our solar system, we are going to have years to prepare for it).
Climate change, while a problem, could potentially kill millions, but we will adjust. 15% at most.
Nope, of all of those options, I don't see any as being able to completely take us out. Now, if aliens with superior technology and a distinct lack of morals come along, we could be toast. In the grand scheme of things, an alien race that is a mere 1000 years ahead of us (which, relative to the age of the galaxy, is a millisecond) in technology could probably wipe the floor with us.
Say they want all our water. 20 ships park in medium Earth orbit (2000 miles-ish) and glass the planet, boiling the water into the atmosphere and then they sit there collecting it. Our nukes currently can only get up to about 750 miles above ground, and even if we modified them, given a 1000 years of technology advance in targeting systems and they could probably pick off our ballistic missles before they leave the upper atmosphere. If the heat / glassing alone doesn't kill us, taking all the water would.
Maybe at the end of 100 years we might have advanced weapons enough to put up an orbital defense, but I think we are still a little too busy trying to figure out how to kill each other instead of a sudden appearance of a hostile alien race.
We are REALLY good at killing things. It's part of the reason that we are the dominant species on this planet. In order for AI to take us out, you are going to need at least 1 fully operational killing-level-sized robot for every 4 humans to come close to a chance at human extinction. That would be 2 billion robots. I just don't see that in 100 years.