Aloha, I've been worrying about that with DS2, who is only a month older than your son, but scraped into this Reception year by 4 hours.
Our sons sound (from posts) fairly similar in where they are reading wise, though I have a feeling that your son sounds more numerate than mine (though even recognising numbers up to 100 was seen as unusual and numbers up to 1000 caused eye-rolling).
In the whole class sessions they are doing stuff like "Who can spell 'it' and 'dog'?", and counting up to see how many objects are left when one has been taken away from a small group. If my DS's teacher thinks he is G&T (or should that be G or T?), in another year your DS will be way off the scale.
That's not much help, is it? For what it's worth, DS2 doesn't seem bored as the whole class sessions are quite brief, but I don't think he's learning much in those bits of the day. On the other hand, he is having a great time playing and improving his handwriting and drawing skills, and making friends.
He is also young in the class (which your DS will not be) and therefore possibly socially more immature than many of his classmates, which gives him his own challenges.
I started another post about how much differentiation is really possible in a large class. We have got stuff to do at home if we want, but he is very tired, and I would like him to do it during the 6 hours he is at school, not the 3 hours he has for play.
Mmm. Not sure if that was at all helpful. Excuse my witterings.