It will likely receive security updates on all 26 capable phones through mid December and the release of 26.2, by which point 26.2 will be released in the second week and will become the new standard upgrade for everyone. At least if past years patterns areanything to go off of, and with Apple, they usually are.
If you are currently on 18.7 you will likely get an 18.7.1 and 18.7.2, but by mid December, these will be no more and the only upgrade path will be to 26.2.
The only devices this is not the case for are devices that cannot update to 26, which will continue to receive 18.7.X and likely a 18.8 next September. These devices are the iPhone XR, XS, XS Max and iPad 7. For these devices only, iOS 18 will likely receive security updates through 2027, and possibly even longer.