Does KPN support connecting fiber directly to the SFP+ port of a Flint 4?

Hi ​@MatijaD, I'm personally not familiar with a Flint router. But you can use your own modem and/or NT/ONT with our connection. As KPN our options to help are limited, but other users might be able to help you.

On our website we have a special page for this aswel, it is in Dutch. At the 'Eigen apparaat instellen’ sub title there is an explenation how to register you own NT/ONT: Eigen apparaat instellen.

We also have 2 articles in our Knowlegde Base that can help you:

Hello ​@Jasper van KPN 
The router in question: https://www.gl-inet.com/en-de/products/gl-be14000
the 1x SFP+ and 1x 10Ge port. 
There is some solutions and so on for sure. Before i try that i was wonder to go official way to try replace CAT.
Will for sure read what you provide. 
Even as much have 10Ge ISP speed, there is still limitation as in hardware support. 

That one looks very nice! I hope the links help with setting it up.