Background: I'm not trans, but have trans siblings, friends, and spouse.

You're off to a great start by using his correct pronouns. That validation probably means a lot to him. Beyond that, just keep treating him like your kid. Ultimately, he's the same person, he's just he now. It might be a little awkward while you get used to his new name and pronouns, but I'm sure he will understand that it's hard to break 15 years of habit. Just keep open communication with him and ask him how you can support him.

Transitioning sometimes gets treated by parents as "a phase" or something that kids are doing to be trendy. Being trans puts a huge target on a person. Being trans in 2026 means being part of a group that is actively and publicly being discriminated against by the ruling party of the US. Coming out as trans is a huge risk, and I don't know anyone who has taken it lightly.

Continue to ask yourself how you can support and advocate for your son. You're going to do just fine.