Per my records, Andrew Painter is Rule 5-eligible this winter. Drafted 2021, signed 7/17/21, at age 18. 2025 will be the fifth Rule 5 Draft since he signed; that means he's eligible, as I understand the Rule.
So yeah, he'll be on the winter 40-man roster. (Or gone, but that's not happening!)
That said... IMHO, he's not ready for a major-league start. There's no reason to rush him; not simply because impatient fans want to see him (without going to Allentown). And they don't need him now.
If the rules hadn't changed - if the roster could expand to 40 after September 1st - there might be an argument for bringing Painter up after the AAA season ends, just to get him past the "Oh wow, I'm in a major-league ballpark!" stuff. But under the current rules... not a good idea, IMHO.
Moreover... Yes, he'll be on the winter 40-man roster. But come February, he'll have to earn a spot in the rotation. Arguably, he should open 2026 in AAA. No longer "working on things," but pitching as he would in the Show, making sure he's fully past the surgery. When he shows that, then promote him. But don't just award him a spot in the rotation because of his pedigree, or because of the hype. Performance, period.