Do you know how this works contract wise? When you get network are you guaranteed that GPON will work or can they refuse service after a certain point in time and force you to upgrade to XGS-PON (or some other standard)?
The contract does not guarantee GPON or XGS-PON. They have a tool to help you figure out what you have, but they can legally change it when they're upgrading their network.
The only guarantee is that they'll give you a new provider owned ONT and router during the upgrade. But that's not very useful if you want to keep running your own equipment.
The provider can upgrade their network from GPON to XGS-PON; in fact KPN (a large Dutch provider) does this regularly, especially in areas with new housing developments.
> The provider can upgrade their network from GPON to XGS-PON
The provider can transparently run GPON and XGS-PON simultaniously because they run on different wavelengths. However unless the provider can tell all existing GPON customers to replace their infrastructure they cannot stop providing GPON. GPON -> XGS-PON is not an upgrade, it's double the infrastructure where the splitter is.
So my question is quite specifically if there is a contractual way for KPN to turn off GPON and force customers to migrate, or if they are required to service both until the last GPON customer goes away on a splitter.
This has been an issue with DOCSIS for in many places of the world where we are already running out of available frequency spectrum.
KPN and other Dutch ISPs don't really care about custom customer hardware, on a practical level and on a contractual level. The Dutch standard is that you use the rented hardware your ISP provides, unless you want something special, then you get specs and settings and you're on your own. Even if you use your own hardware, you often still get a modem delivered to your doorstep.
If anything breaks on the network side, the troubleshooting procedure is "connect the hardware we sent you and see if it works". If it does, it's up to you to fix your side. If that requires new hardware, you're kind of screwed. KPN has the obligation to permit you to run your own hardware and to provide you with the information necessary, but not to keep any kind of backwards compatibility.
(Euro)DOCSIS should be backwards compatible, but things like radio channels and unencrypted video signals have already been replaced by their digital equivalents to add more upstream capacity by Ziggo (the last remaining large Dutch cable company). This broke functionality for a whole bunch of devices, but these changes were announced months in advance so customers had to choose between ending their contract and taking it.
The trouble with dealing with KPN is that KPN is also the company operating the POPs in most places, with many other ISPs leasing their lines. So even if you switch to a different ISP in protest of the XGS-PON switch, you're very likely to still end up with a XGS-PON signal from KPN.
You're almost certain to end up with the exact same line just a different provider on it. Very few areas have multiple fiber networks, although it's getting more common.
I still believe that the original move, forcing KPN and other network owners to allow competitors on their network, was a better option than digging up the streets twice to get two fiber networks in place.
Consumer contracts don't guarantee GPON support in any way. So if KPN wants to upgrade they can just send the customer a letter telling them to get an XGS-PON compatible ONT by some date.
They'll probably take a bit more customer friendly approach and at least send you a free provider owned XGS-PON compatible one and a new modem. But for your own equipment you have to manage everything and make sure it complies with their published specifications.
That sounds like a somewhat pragmatic approach. Curious to see how that plays out in practice. I presume the total number of consumers that are interested in running their own ONT is limited. In Germany the situation seems a bit different. There customer owned Fritzbox devices with integrated ONTs are very widespread making the situation for an ISP quite different when it comes to upgrades.
Sure, but even with the fritzbox situation all ISPs also offer dedicated ONTs as free rental or for 40€ as purchase. Some, e.g. Telekom, also offer SFP ONTs (Digitalisierungsbox Glasfasermodem)