From: https://docs.turris.cz/#updates

We are committed to providing long-term support for our devices for as long as the Linux kernel continues to support them. For instance, our initial router, Turris 1.X, which was a part of the Turris security research program launched in 2013, is still supported after a decade.

I guess it's something along "we will try to support your device for as long as humanly possible" ? My ~three years old omnia is still getting updates (just like a regular linux box would), actually seems I have one pending right now:)

I’ve had mine since 2018 and it’s still going strong! I’ve recently upgraded it to WiFi6 but otherwise it’s the same device.