Hi, Macy! I'm with Kaiser NorCal. They use a modified informed consent model, often putting a patient on HRT after just a couple sessions with a gender therapist.
My experience was a little different, partly because of my own actions in delaying HRT.
I had an initial contact with a generalist therapist, for suicidal depression and anxiety. I came out in my first session, and he mentioned the gender specialists. We did a few more sessions to help me with coping with the depression and anxiety. In my particular case, I was not put on antidepressants or antianxiety drugs as he felt the cause was likely external (that is, my gender dysphoria and the stress from being in hiding, rather than organic and being amenible to medications).
I was referred to the gender therapist, and during my intake with her I mentioned that I would be interested in HRT eventually, but wanted to wait at least a few months and make sure that I was really being driven by gender dysphoria and not something else. At this point my wife had already put limits on me, including 'no HRT.' She dropped that constraint after my second run at suicide a few months later.
After that, I thought that perhaps I should try HRT, as I had understood that it often helped with the depression and anxiety. I went so far as to write my own 'referral letter' to try and demonstrate that I knew what was involved. I went into my next appointment with the gender specialist, and after the 'check in' ritual, said I wanted to ask about something. She immediately said:
"Oh, do you want to start HRT?"
"Yes, please!"
"Just a sec..." She turned to her computer and typed for a second. "Do you prefer morning or afternoon appointments?"
"Um... Morning?"
"How does tomorrow at 10 AM sound? Dr. Che is a good endocrinologist here."
"Um... Yes, please!"
That's about as close as I've gotten to formal letters.
The approval process for FFS and GCS was simlar. I met with a psychologist who went over my record, and was put on the queue to meet with the appropriate surgeons. I've already had the FFS meeting and am now in the queue to have FFS scheduled. I will be meeting with the GCS surgeon in a few months.
Everything is in the electronic records system. I'm sure they could produce a formal letter if needed, but in their system, I've never seen one.