Brooks Glycerin StealthFit GTS 21 Review: Soft, Supportive, and Shockingly Responsive
GEAR & SHOE REVIEWS
When Brooks describes the Glycerin StealthFit GTS 21 as “super soft, supportive, and sleek,” I’ll admit I wasn’t sure what to expect. I received the shoe months ago for review, and although it wasn’t paid content, I pushed it to the back of my closet—mostly because the plain white color didn’t inspire a lot of excitement. But once I finally started running in it, I was surprised by how quickly it became a regular part of my rotation.
This model sits within Brooks’ long-standing Glycerin line, a family known for cushioned daily trainers. The GTS designation (“Go-To Support”) adds stability through Brooks’ well-known GuideRails system—a feature intended to gently align runners who need a bit more structure. Even though I have a neutral gait, this shoe ended up highlighting how much that extra support can matter on early-morning runs when form hasn’t quite woken up yet.
Model & Purpose
The Glycerin StealthFit GTS 21 is built as a versatile daily trainer: long runs, short runs, easy mileage, and everything in between. Its mission is simple—deliver plush cushioning, a smooth ride, and quiet stability without forcing the runner into a rigid motion-control setup.
The StealthFit variation offers a sock-like upper rather than a traditional tongue, giving the shoe a completely different feel compared to the standard Glycerin 21. If you’re a runner who loves a compressive knit that molds around the foot, this might be the more appealing version.
Specs at a Glance
Weight: ~8.9 oz
Drop: 10 mm
Support: GTS (GuideRails) stability
Foam: DNA Loft v3, nitrogen infused
Upper: StealthFit knit, compressive and sock-like
Price: $160
Colors: Limited — primarily white/gray/black
The 10 mm drop is higher than many modern trainers, but it pairs naturally with the rocker, especially for heel strikers. Despite offering both cushion and support, the shoe remains lighter than you’d expect.
Upper & Fit
The StealthFit upper is immediately noticeable. It’s stretchy, sock-like, and molds to the foot in a way that makes lacing almost secondary. As someone who often runs barefoot in my trainers, I appreciated how smooth and seamless the interior felt. No hotspots, no rubbing, and no need to stop mid-run to readjust the laces.
Once on, the shoe fits like a glove—secure without squeezing, flexible without feeling sloppy.
Midsole & GuideRails Support
Brooks’ nitrogen-infused DNA Loft v3 foam sits at the heart of the ride. It’s soft but more responsive than traditional marshmallow-style cushioning. The GuideRails system adds support without pushing the foot in any unnatural direction. Instead, the shoe simply keeps you aligned—especially helpful on days where form is a little sleepy.
Even though I considered myself solidly neutral, I found the support surprisingly welcome. On early morning runs, I felt stable and “ready” much sooner than usual.
Ride & Performance
My first run in the GTS 21 immediately revealed a subtle rocker that I didn’t expect. That gentle forward roll kept me moving effortlessly—almost like a toned-down version of what super shoes offer. Paired with the foam, the ride felt cushioned yet lively, soft without feeling sluggish.
Over roughly 300 miles, I came to trust the shoe as a reliable daily trainer. There’s a bit of flexibility in the forefoot that gives good ground feel, the cushioning doesn’t bottom out, and the outsole durability has been excellent. I avoided running in the rain simply to keep the white upper clean, but performance-wise, the shoe held up better than I anticipated.
One thing I didn’t expect: my husband tried the shoe as well, and he noticed the same rocker and responsiveness immediately. It’s subtle, but once you feel it, you can’t un-feel it.
Comparison to Other Shoes
Brooks Glycerin 21
Compared to the standard Glycerin 21, the StealthFit GTS version feels:
More compressive due to the knit upper
More stable thanks to GuideRails
Lighter and slightly more responsive
A bit firmer than the standard version, which leans softer
Hoka Bondi
Both shoes aim for max cushion—but deliver it differently:
The Bondi is softer, cloudlike, heavier, and more of a dedicated recovery or slow-run shoe.
The Glycerin GTS 21 is more responsive, lighter, and better suited for a wider range of daily mileage.
Hoka’s traditional upper is more structured; Brooks’ StealthFit is more minimal and sock-like.
Bondi is neutral; GTS has noticeable support.
First Impressions
I originally dismissed the shoe because the GTS system made me think it wasn’t “for me.” But after a few runs, I realized the support didn’t interfere—it helped. The shoe also surprised me with its responsiveness, the gentle rocker, and the secure upper. What looked plain and boring in the box became one of those shoes I ended up reaching for far more often than expected.
Pros & Cons
Pros
Responsive yet cushioned ride
Rocker design helps maintain momentum
Excellent outsole durability
Comfortable StealthFit upper ideal for barefoot running
Supportive without being intrusive
Great for daily mileage and long, steady efforts
Cons
Limited color options
Not ideal for racing or speedwork
Heavier feel compared to performance trainers
White upper stains easily
Bottom Line
The Brooks Glycerin StealthFit GTS 21 is an excellent option for runners seeking a cushioned, supportive daily trainer that can handle high mileage without feeling bulky. With its nitrogen-infused foam, subtle rocker, and sock-like upper, the shoe strikes a balance between softness and responsiveness that makes daily runs feel smooth and efficient.
It isn’t a racing shoe and it isn’t trying to be—but as a workhorse trainer with durability, comfort, and quiet stability, it delivers exactly what most runners need for everyday training.