plwww, I sympathize with you on this. Firstly, AT&T techs doing a hard-sell on AT&T's own lines as a solution to all problems (even trying to sell me their 1 G fiber despite there being no fiber on the block). Secondly, having previously read through your
thread on AT&T woes with Legacy DSL, I can say that I now have a much greater hands-on experience with being strung along by the AT&T infrastructure "mystery box".
We are still desperately clinging to our own Legacy DSL (6 Mbps line, 5.1 Mbps max download, 0.7 Mbps max upload) with no upgrade options in sight. I am loathe to discontinue Sonic due to their customer service, accountability and ethics. Our line has been 99.99% rock-solid with Sonic since early 2012. In December 2020 things started going south with a number of outages. One was due to AT&T "closing" our port with no explanation. Then we had a complete AT&T service failure for roughly 5 months (July 21 - Dec 8, 2021) that required us to rent service from a neighbor. Within 2 blocks is 1 G fiber that was installed years ago. There has been no movement since that time.
(NOTE: During the long outage mentioned above, Sonic CS was responsive and did their best to help, but I did hear "Legacy DSL will end soon" a number of times. Sonic also suggested looking for alternate internet service to resolve our outage, even though that would be with a competitor.)
The areas around us that have 1 G fiber cannot initiate service with Sonic. We are one of the towns that has some kind of AT&T agreement with the county that excludes competitors using their lines. Only grandfathered accounts such as ours are allowed to continue ... for now. I believe Fremont and Pacifica are among the cities that cannot have new Sonic service at this time. When I talked with my city's IT manager, they did not have knowledge of why this was, just that it was handled by the county or higher up the chain.
AT&T Fiber is very random from my perspective (and that of various AT&T employees whom I have spoken to candidly and off-the-record over the years, including those who work with the high-end fiber lines, not just those you see draped across your street poles). AT&T will rush out fiber lines in some areas and streets, then suddenly stop with no explanation, often leaving one house with 1 G fiber, next to a house that can barely get 1.5 Mbps Legacy DSL.
I guess the bottom line is, you will know when AT&T starts marketing to you about upgrading. And even then, if Sonic does not already have the ability to offer service in that location, you will have to make a decision.
PS. A family member with U-Verse for phone, internet and TV had their phone go out and AT&T tried to convince them that upgrading to their new Fiber would "fix" the issue. The resolution required my intervention and insistence on toggling of various account settings on AT&T's side to get it working again (account re-initialization, then forwarding of the phone, then un-forwarding to restore dial-tone). No one can explain how/why it happened.