Crack in rim

nah.... get a new hoop...

I’ve put over 100 hours on a rim like that in off-road , not mx . I drilled a small hole at the end of the crack to keep it from spreading further , which it never did. My crack did not go beyond the flat section of the rim , hard to tell if yours goes beyond that.

Run it.

Could you? Yes. Would I? No

i would run it and replace it as soon as you can. I think it will hold together for a few rides but better safe than sorry. To run it for one ride......i would do it without question.

trails? sure, i'd chance it for a bit.

jumping much? nope.

I just found out I have a crack identical to this one on my rear rim. I have no idea how long it has been there. Anyone else have any experience on welding these and how long they hold up?

I have welded a KTM rim before. It was a big pain in the ass and then just cracked again first ride back.

Have welded a lot of rims when sidecar racing, they cracked often due to the higher loads, raced with completely broken rims as well - never a problem. If welded with proper equipment and done right, they will not crack again but the rim loses some of its temper due to the heat involved. Ask yourself where should one or both ends of your rim escape to? The rim is held in shape by the tension of the spokes and if you have properly adjusted spokes nothing could happen, it needs a couple spokes to break and a deflated tire before there is any chance that those ends will overlap when hitting a hard bump.
BTW - on high end bicycles the rim is not welded at all, just a connector between the ends and the spokes pull it all together and keep it in shape.