My son (who is now 10 and a Davidson Young Scholar) was diagnosed with autism at that age also. I have other posts on here about our journey, so a lot of this may have already been said.
First of all, my son was nonverbal at the time of diagnosis (unlike your little guy who already has a huge vocabulary.) We did LOTS of ABA at that age. He attended ABA therapy for 4 to 6 hours at a time 3 days per week. He LOVED the therapy! As shocking as it may seem for a kid under the age of 3 to be able to "endure" 6 hours of therapy, he thrived. He became verbal very quickly which is when we realized how quick of a learner all around he was (is).
When he was a little over 3, a spot opened up in an autism school. Before that, he was in a special needs classroom which was a disaster. The autism school helped him grow by leaps and bounds. He then was ready to be mainstreamed and attended a regular preschool. (Looking back, we should have tried to get him into Kindergarten, but we didn't.) Once he was in public Kindergarten, he was re-evaluated and determined to be gifted. Then in 1st grade, he was tested again and we were told he was exceptionally gifted.
Since 2nd grade, he has attended a public school for the gifted with speech, OT, social skills provided through his IEP. It is not perfect, but ok for now. We do LOTS of enrichment at home on weekends and especially during the summer to make up for the lack of academic challenge.
Anyway, it sounds like your kid is similar, so I'd be happy to answer any questions here or privately.
Kate
