For most of the cheap routers the manufacturers offer updates just for about two years. They want you to buy a new one every two years. AVM (Fritzbox) provides updates for up to 10 years. If you go for a more professional model, like LANCOM, you'll get also about 10 years. Telco branded routers are usually supported for a few years. One of the worst manufacturers is DLink. Many security issues (often fixed only after media coverage), poor WiFi performance, hardware-wise at the low end (often half the flash and memory compared to other manufacturers' models in the same price class) and don't expect to get updates for more than two years, even for expensive models.