If you enable automatic updates, you still have to trust that the GrapheneOS devs won’t push a malicious update to your phone, or sell that ability to someone else.

Yes some trust of the project is required. Consider what would motivate them to do something malicious. They do not know who is using the OS since these phones are anonymous and the user base is relatively small. Neither targeted surveillance nor bulk collection is really possible because of this.

The code is completely open source. With the most paranoid of us using and reviewing the code, any malicious code inserted would immediately kill the entire project. We can install and switch to another OS anytime we need to.

Why do you think you can trust the hardware? What about E911, etc.?

Yes we are using the same closed source hardware as 99% of people. Open source HW is ideal, but the options are currently very limited. I use rotating burner SIMs on occasions when I need cellular and never make calls with the SIM. The OS provides other SW mitigations for the HW such as no SW access to the device ID's, fine grained app firewall, and ability to turn off all cellular but enable WIFI.