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| Garmin’s Descent Mk3 dive computers are receiving the v25.21 update |
If you’re a serious scuba diver who also happens to wear your tech on your wrist, you’ll want to pay attention. Garmin has just rolled out System Software 25.21 for its popular Descent Mk3 and Descent Mk3i watch-style dive computers, and this update is packed with genuinely useful features. It’s the second stable release of 2026 for these wearables, following hot on the heels of version 25.14 (which mostly focused on squashing bugs). Now, Garmin is shifting gears and adding functionality that actually changes how you dive.
What’s New in System Software 25.21?
Let’s cut straight to the chase. The headline feature for both the Descent Mk3 and the Mk3i is something called Dive Setup Sharing. This is one of those “why didn’t anyone think of this sooner” ideas. Essentially, you can now copy your entire dive setup—gas list, conservatism settings, and other critical parameters—to another Garmin device. If you’re diving with a buddy who has the same computer, or if you’re an instructor setting up multiple units, this saves minutes of fiddling through menus. Just beam your profile over and go.
Beyond sharing, Garmin has also refined how the Gradient Factor 99% (GF99) data is displayed when you’re back at the surface. For the uninitiated, GF99 tells you how close your tissue compartments are to the deco limit. The update ensures that this data remains accurate and readable even after you’ve surfaced, which is a subtle but welcome tweak for safety-minded divers.
Exclusive Upgrades for the Descent Mk3i (The Dive Computer That Does It All)
Now, if you own the higher-end Descent Mk3i, you’re getting an extra helping of features. First up is Sidemount support. This isn’t just a marketing label—the Mk3i will now actively notify you when there’s a pressure difference between two linked tanks. Sidemount divers know that managing tank imbalances is critical, and having your wrist computer alert you before you run into trouble is a game-changer.
On top of that, Garmin added a new data field called Redundant Time Remaining (RTR). RTR is a more conservative, safety-oriented calculation of how much dive time you have left, factoring in gas supply and decompression obligations. It’s perfect for tech divers planning multi-level dives or deco stops.
There’s also a much-needed stability improvement for the Descent S1 buoy accessory. If you use the S1 as a surface marker buoy that communicates with your watch, the connection is now rock-solid. No more dropped signals when you need them most. And finally, Garmin fixed an annoying bug on the Mk3i where the dive log could show incorrect final tank pressure values. Your logs will now accurately reflect what your gauges say.
How to Get the Update
Ready to install? System Software 25.21 is available right now for all users of the Descent Mk3 and Mk3i. You can grab it through any of the usual channels: the Garmin Dive app, the Garmin Connect app (on your phone), or Garmin Express on your computer. The update is free, as always.
If you’ve been on the fence about picking one of these dive computers up, now might be the time. You can find the Garmin Descent Mk3i (currently priced at $1,399.99) over on Amazon. Check the latest price and availability here – it’s the same model that just got all these new features.
Final Thoughts: A Human-Friendly Update
What I appreciate about version 25.21 is that it doesn’t feel like a “tick-the-box” firmware release. The Dive Setup Sharing feature alone will save dive crews hours over a season. Sidemount support on the Mk3i shows Garmin is listening to technical divers, not just recreational ones. And fixing that tank pressure bug? That’s just good housekeeping.
As always, Garmin has published the full release notes on their community forums. You can dive into the nitty-gritty details right here.
So whether you’re planning a wreck penetration next weekend or just logging shallow reef dives, fire up Garmin Connect and get that update installed. Your dive computer just got smarter.
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| The release notes for Garmin Descent Mk3/Mk3i System Software 25.21 |