From my experience and from what autistic adults have said, knowing about their diagnosis has been very helpful. It helps to explain why they have certain difficulties, so they don’t think they are ‘mad’ or in the case of one girl ‘evil’ . If individual is more aware, they can also learn about their specific challenges and how to manage them independently. When explaining need to emphasise that they have differences rather than difficulties.

I have a daughter who is very high functioning (more so now at age 17 than she was at 9, when meltdowns were routine). She sometimes denies that she is autistic but learning and sharing the diagnosis with her was an overwhelmingly positive experience. It took the pressure off of her to change and fit in and meet all neurotypical standards. She was 15 when we first started talking about autism so it is very different than telling a 9 year old. But I think it will be worth it to have the conversation earlier rather than later. It's a tool for self-understanding and self-acceptance.

I think its already a good situation when you can start to consider thinking of whether to explain to your son that he has autism (even though he still suffers meltdown).
I mean the fact that you are considering whether to tell him or not, means something positive, he must be rather quite good in understanding language, general knowledge and so on.

Anyway, as all our other dear friends mentioned above, i think its good to let him know so that he can regulate himself.

Does he have a good grasp of what things are correct and wrong to do? Or whats not nice and so on? (Doesn't matter if he still does something wrong due to lack of control)
If he has that kind of understanding, then I think its good to let him know.

Just a suggestion, might work or might not work....
Taking videos of example of behaviors not encouraged from youtube, or video of himself,...
then show it to him when he is calm.
Explain slowly why it's not appropriate to do that, because it disturbs other people in public.
If he has got good self awareness, maybe it may eventually start to get into his head that he needs to self regulate (with your help on how to do it).

Hope this little suggestion may help.

I read my son the book called all cats have Asperger
By kathy hoopmann
I then read it to his class. That was 12 or 13 years ago... best thing I could have done. All the teachers in the building read it and I donated copy to school library.

They know... you just need to explain what he CAN do to help himself