Garmin Descent Mk3/Mk3i Update 25.21 Adds Dive Setup Sharing and Sidemount Support

Garmin has rolled out System Software 25.21 for its Descent Mk3 and Descent Mk3i dive computers, marking the second stable update of 2026. Following the bug-fixing System Software 25.14 release, this latest update introduces several new features and improvements designed to enhance the diving experience for both models, with some exclusive additions for the Mk3i.

One of the headline features in this update is Dive Setup Sharing, which allows users to copy critical dive information between Garmin devices. This includes gas lists and conservatism settings, making it easier for dive buddies to sync their equipment configurations before heading underwater. The feature is particularly useful for group dives where consistency in settings can improve safety and coordination.

Both the Mk3 and Mk3i models receive improvements to the Gradient Factor 99% (GF99) data displayed at the surface. This enhancement provides divers with more accurate decompression information during their surface intervals, helping them make better-informed decisions about their next dive.

For Mk3i owners, the update brings support for Sidemount diving configurations. This specialized diving technique, popular among technical divers, involves carrying tanks on the sides of the body rather than on the back. The Sidemount feature includes pressure differential notifications between two linked tanks, alerting divers when there's an imbalance that could affect their dive profile or safety.

The Mk3i also gains a new Redundant Time Remaining (RTR) data field, providing divers with an additional safety metric that shows backup time calculations. This feature is particularly valuable for technical diving scenarios where precise time management is crucial. Additionally, the Mk3i sees enhanced connection stability with linked Descent S1 buoy accessories, improving the reliability of surface marker buoy operations.

Garmin has also addressed a specific bug in the Mk3i model where dive logs could display incorrect final tank pressure values. This fix ensures that post-dive analysis and record-keeping remain accurate, which is essential for divers tracking their gas consumption over time.

System Software 25.21 is available now for all Descent Mk3 and Mk3i users. The update can be installed through multiple channels: the Garmin Dive app, the Garmin Connect app, or the Garmin Express desktop software. This multi-platform approach ensures that users can update their devices regardless of their preferred management method.

The Descent Mk3 and Mk3i represent Garmin's premium offerings in the dive computer market, with the Mk3i currently priced at $1,399.99 on Amazon. These updates reinforce Garmin's commitment to maintaining and improving its high-end diving equipment through regular software enhancements.

For divers who rely on these sophisticated tools for both recreational and technical diving, the new features and improvements in System Software 25.21 offer tangible benefits in terms of safety, convenience, and dive planning capabilities. The addition of Sidemount support and Dive Setup Sharing, in particular, demonstrates Garmin's responsiveness to the evolving needs of the diving community.