Will I have to pay a yearly fee to keep a Sunseeker X5 running?

With the X5 Gen 2, yes, after two years. The Gen 2 Sunseeker X5 gets its positioning corrections as network RTK over a built-in 4G connection, and Sunseeker bundles 24 months of that service. After that, Sunseeker's product page states that an active subscription is needed for continued use, so the fee isn't optional if you want it to keep mowing.

Sunseeker quotes the renewal price in euros on its product pages and publishes no sterling figure, so ask your dealer what it will cost in pounds. The subscription covers both the RTK corrections and the 4G link, which also runs the GPS tracking and geofence alerts.

The first-generation X5 works differently. It uses its own RTK antenna in the garden, 4G is an optional add-on, and Sunseeker doesn't require a subscription for it to mow. If a dealer still has Gen 1 stock, that's the way to avoid the fee, at the cost of a more involved installation. Gen 2 does gain day-and-night obstacle sensing, though.

Sunseeker also sells an antenna kit as an accessory, but doesn't say whether fitting one lets a Gen 2 mower keep working without paying. Until Sunseeker clarifies, assume it doesn't. When you're comparing costs over five years or so, add the subscription to blades and electricity; our running-costs calculator can help with the rest.