To let my 4yo read when he can't sleep?

[Dinosforall]

DS1 sometimes has trouble dropping off, and lately has also occasionally been waking for long stretches at night.

Sitting with him sometimes helps, sometimes not. He generally seems fine the next day ( unlike his parents ). He is a confident reader and will sit in bed with a pile of books.

He starts school next month and obviously we want him fresh (though hopefully it will wear him out!) It feels a bit weird to let him stay up but otherwise he just stares at the ceiling and keeps waking us.

AIBU to let him read at night and just be glad he's getting some practice?

I don't think sitting up reading for hours in the middle of the night is a great idea if a 4 year old. It's not awful but like others said encouraging him to drift back off to sleep with gentle music or perhaps an audiobook might be better at that time of night. My DD is an early riser and reads in bed before the rest of the house wakes up but thsts different imo.

I'd let him read before he goes to sleep. I always used to read to my children at night and then let them read to themselves. It's a habit they've kept as teens.
I'm not sure about letting him read if he wakes in the night though as it might encourage him to wake. However if he wakes anyway at least he's doing something quiet and relaxing.

Absolutely.

I used to when I was younger and I loved it. My dad often used to come and tuck me in and I'd be asleep with a book on my face snoring

I would consider an audiobook instead.

The good thing about audiobooks is that you can lie down with your eyes closed and the light off and still enjoy them.