Fiber can certainly suffer from the exact same issues as copper - a neighborhood or group of homes or town or whatever connects to the Internet over a single piece of cable or logical connection, or a single piece of equipment, and those can become congested.

In theory, that could limit your maximum available bandwidth by limiting everyone’s bandwidth.

But with Fiber, the infrastructure is newer and generally installed with future capacity in mind. Also, fiber is cheap and labour is expensive, so the fiber from your home may continue for some distance before it reaches the first piece of powered equipment, which helps make a physical fiber network more economical, and more redundant.

When you were getting 800-980 speeds. How many devices was connected? How many now? Have you added any new plugins to your browser? Did you test on different browsers? Try different speed test sites? Try a live boot of a Linux flavor to weed out anything that might be Windows related?

You can live boot distros like Mint, and Ubuntu both very user friendly Linux. Test speed that way. If your internet speed is back up, your speed decrease is on Windows side.

I haven’t seen my connection be less than a gigabit in either direction for the last 10 years. Fibre is non-negotiable when I’m moving into a new place now.

It may be purely coincidental but once I upgraded to fiber I was behind a cgnat. I wasn’t able to share self hosted services. I was consistently getting only 500-600 Mbps. I had to purchase a static IP from my ISP and from there I was able to achieve 800-900 consistently. Might be an option.

When I upgraded to fiber gigabit my, not very old, router was the bottleneck. I am have consistent 900s speed with good gear.

Many people seem to get consistent “full” gigabit speeds around the clock with FiOS, but I do see slowdowns, regularly. Definitely slower during evenings and weekends vs during weekdays here in the south end of Richmond, VA.

I have never seen download speeds over 850 (direct from the ONT, local Ookla speed test server, using various computers) and my service more commonly tests in the 650 to 750 Mbps range, I do see dips in peak periods down to the upper 400’s. These speeds have gradually trended lower in recent years. Verizon has come out a couple of times to check stuff and each time they say everything is working fine.

This week one of their bucket trucks snagged a low-hanging line in my alley, pulling down a span of overhead fiber and old copper lines, which in the process tore their box off the side of my house, pulled off some siding, and yanked a knotted bundle of excess fiber patch cable out of my router though a small hole in my exterior wall and out into my yard. They just finished replacing three spans of aerial fiber (“squirrel damage” lol) and replaced everything from my ONT to the pole. No notable difference in performance since the rebuild. Whatever is constraining my network speed is at least something at the neighborhood level, not my connection.

tl;dr: While it seems uncommon, yes, there can be some variability to FiOS speeds.

None of the major ISPs offer SLAs (service level agreements) with throughput guarantees for residential service. You’ll hear anecdotes from people here about their performance, but this is specific to their market and their specific network segment. You can’t make the leap from those anecdotes to “service type X is better” because it’s not the service type that’s delivering more throughput; it’s the ISP network design.

Here’s the thing. All residential internet works over shared medium networks. The wire or fiber that goes back to the distribution node is shared amongst your neighbors. For fiber, it’s called a PON (passive optical network). For cable it’s called DOCSIS (please don’t at me if you’re an engineer, I’m generalizing). These networks use a shared physical layer to supply data to the last mile.

So your actual throughput is usually limited by two factors:

1. Traffic on your local loop / PON.
2. Provisioning limitations at the distribution node.

ISPs routinely oversell the throughput available on these networks. It’s how they turn a profit. Getting good speeds is a matter of finding the provider with the least over-provisioned network in your area. That last part is important. An ISP can be good in one region and lackluster in another.

All that said, fiber networks tend to be newer, so it takes time for ISPs to sell them out. For example, if the cable provider in your area had a near monopoly, then the local phone provider rolled out fiber, it’s going to take time for people to switch. You can take advantage of that by adopting early. Just understand that your network performance will degrade as more people switch and you end up with more network contention.

Fiber can be oversold just like any other internet connection type.

There are different types of fiber out there in the wild. Yes the physical cable is the same but deployment is different. There is shared fiber that will say speeds are “up to” such as Google and municiple fiber and then there is dedicated which is guaranteed. Dedicated will come with service level agreements. That’s why you can see different pricing for different fiber services. Shared fiber might be amazing for a time but will eventually get oversubscribed and start to vary more usually because the provider is borrowing the network. They need to get a certain number of customers before they can borrow more bandwidth which usually doesn’t happen. These networks usually don’t get upgraded over time

I use wifiman.com, it’s a Ubiqity website. Fiber is still “up to” speeds. Like other people have stated there are a lot of variables in the signal. But still should be pretty consistent. But unless you have multiple people gaming at the same time you do not need Gigabit speeds. No media take that much speed. 4K movies only need on average 40Mgb.

It’s best effort. Not sla guaranteed service.