Are the negotiated prices secret? I've never had a major hospital visit. But every time insurance has covered something for me, I could look on my account claim

Are the negotiated prices secret? I've never had a major hospital visit. But every time insurance has covered something for me, I could look on my account claims and see both the official price, and the negotiated price. I also had an "amusing" experience with my dental insurance, where my provider went out of network, and I didn't know until I was in the chair (at which point I was at least asked before they proceeded). When I went to pay, they gave me a bill that listed only something to the effect of "anticipated insurance payment", which is what I was charged. They also filed an insurance claim on my behalf, which was eventually reimbursed fully. However, when I got the reimbursement notice from my insurer, it list a cash price about 50% higher than what I paid, which my insurance company was able to negotiate down for me.