My son is 2.5. He says only same 7 wds. But has said many. Imitates me. Receptive language great. History speech delay w bro. No gdd. Autism r/o. Worry?

Speech delay. I would definitely check in with his doctor. Sounds like at a minimum he will need some speech therapy.
Evaluation needed. Speech delay can be caused by autism or another developmental disorder. In the us the early intervention program provides free comprehensive evaluation to children under the age of 3. Check with your local health department. No matter what the cause, it is best to address it early.