OP, you’ve ignored questions about your ds’ social abilities and personal care skills.
It is clear that your ds is academically well ahead of where he will need to be in reception, but academic skills alone are not going to ensure he has an enjoyable time at school, particularly in reception.
Can he:
recognise authority, and know that he needs to follow the rules/instructions, even if he thinks there is a better way, or doesn’t understand why he is being asked to do it that way?
can he sit quietly, without interrupting with ‘facts’, while a teacher explains a concept?
can he listen to a story all the way through without interrupting with a million questions and tangential thoughts?
can he recognise that there is a time for questions (and that it isn’t always a time of his choosing)
can he accept not always being right?
can he accept that while he may well be the best at reading, he might not be the best at model making, running, role playing, etc?
can he accept that a large part of learning for a lot of children in reception is trying, failing, and working out where it went wrong (in the case of model building)?can he understand that the teacher won’t necessarily correct children ‘doing it wrong’, because the learning curve from getting your idea out there, seeing it through, and troubleshooting what could be done better is more valuable than just telling the children the ‘right’ answer?
does he have any sensory difficulties? Carpet/circle time has been difficult for all 3 of my ASD children, for various sensory reasons. (As has using the toilet at school, eating in the dining hall (both food issues and sensory - noise and smell) and swimming lessons)
can he tolerate other children knowing less than him on a topic, without making them feel inferior?
how are his gross motor skills? Is he sporty? If not, how will he react to others being better than him?
Is he a perfectionist? Two of my dc have/had huge issues with it getting things right straightaway. The crash and feelings of abject failure are not to be underestimated. My middle child (not in reception at the time!) told me very seriously that she felt she had done really badly in a test, and that her teacher was going to be cross with her. Surprised (she is effortlessly top of the class, usually) I proved a little further. Turns out she had ‘only’ got 97%, and felt she had failed because for once someone had got a higher mark than her. It really felt like failure to her at that time.
Will he be able to work in a group with other children, and let them share ideas, even if he feels he knows more/best?
Can he recognise when people are just not that interested in his eleventy billion facts about a topic, and stop talking? Can he let others take turns in conversation, and is he able to think flexibly when conversations go off at a tangent?
And that’s all just off the top off my head. If the answer to any of the above is ‘no’, then that’s what you need to work on before he starts school.
Incidentally, does he know he is autistic? Because if not, you might want to start exploring the topic with him. He is about to be put into a class of 30ish children, and may well start recognising that he does not think, feel, or process things the same as most of the other children. Mental health shouldn’t be overlooked, and feeling like you don’t fit in is very difficult. If he does need any adjustments make sure he is comfortable with it happening - one of mine cannot bear to stand out/be seen as different, while another (currently in year 1, so have recent reception experience) couldn’t care less, and eg happily wears ear defenders when needed and just tells people “I find things too loud somethings, and these help” - his sister, with the same auditory issues, would rather die than be so upfront about it.