How can I help my autistic son learn to read when he memorizes everything but doesnt decode?

My son is 6 and autistic, level 1 with strong language skills. His therapists keep telling us he has hyperlexia signs without actual hyperlexia. What that means is he can recognize a huge number of written words on sight because his memory is unbelievable, but when you put a brand new word in front of him that he hasn't seen before, he cannot sound it out. He just stares.

His teacher flagged this in march and I've been trying to figure out what to do since. Most of what I find online is for kids who are behind on letter recognition. He's the opposite. He knows his letters and can read sight words and whole sentences he's memorized. He just can't decode an unfamiliar word.

The frustrating part is that everyone treats him like he's a reader because the surface presentation is so strong. Teachers don't always catch what's actually going on until you put him on the spot with a nonsense word and watch him freeze. We're heading toward a sit-down with his IEP team in September and I want to be specific about what Im asking for. Would be grateful for any advice from parents who have kids on the spectrum