The EVO is the newest and smallest Litter-Robot, launched alongside the 5-series in late 2025 as Whisker’s entry point. It looks like a shrunken Litter-Robot 4, and in most respects it is — but the trims Whisker made are specific, and a couple of them matter more than the footprint does.

Quick Answer

Buy the Litter-Robot EVO if you have one cat under 19 lb and floor space is the constraint you’re actually solving for. Buy the Litter-Robot 4 if you have two or more cats, a cat over 19 lb, or you want litter-level sensing and the ability to add accessories later. The EVO is not a stripped-down machine — it cleans the same way and runs the same app — but its 2-cat ceiling and 19 lb weight limit are hard walls, not soft recommendations. If either one applies to your household, the decision is made for you before price enters the picture.

Litter-Robot EVO vs Litter-Robot 4: Spec Comparison

Spec	Litter-Robot EVO	Litter-Robot 4
Footprint	20.6 x 24.3 in	22 x 27 in
Height	27.6 in	29.5 in
Entryway	14.85 x 14.85 in	15.75 x 15.75 in
Interior globe height	14.5 in	16.5 in
Cats supported	Up to 2	Up to 4
Cat weight range	3–19 lb	3–25 lb
Waste drawer interval, one cat	Roughly every 7 days	Roughly every 8 days
Waste level sensing	Full-drawer notification only	Detailed waste-level monitoring
LitterLevel sensing	No	Yes
Automatic LED night light	No	Yes
Full-color LCD display	Yes	No
WasteID (urine vs. feces)	No	No
LitterHopper / Shield accessory support	No	Yes
Trial and warranty	90-day in-home trial, 1-year	90-day in-home trial, 1-year
Price Tier	Budget	Mid-range

Two rows in there surprise people. The EVO — the cheaper box — is the one with the full-color screen; the Litter-Robot 4 doesn’t have a display panel and leans entirely on the app. And the EVO’s waste drawer isn’t dramatically smaller in practice: one cat’s worth of waste, roughly a week versus roughly eight days.

Space and Fit: the EVO’s Real Argument

The EVO takes about 20.6 by 24.3 inches of floor and stands 27.6 inches tall. Against the Litter-Robot 4’s 22 by 27 inch footprint and 29.5 inch height, that’s not a trivial shave — it’s the difference between fitting in a half-bath alcove or under a low shelf and not fitting. If you’ve been putting off an automatic box because the ones you measured wouldn’t clear a vanity or a closet doorway, the EVO is the model to measure again for.

The catch is that the shrink is not only external. The entryway drops from 15.75 inches square to 14.85 inches, and interior globe height falls from 16.5 to 14.5 inches. Two inches of headroom is a lot to a cat that likes to stand up or turn a full circle before settling. For an average-sized adult cat that’s a non-issue. For a lanky, tall, or long-tailed cat it can be the thing that makes them refuse the box entirely, which is the most expensive failure mode in this category. Ohio State’s Indoor Pet Initiative sets the baseline bluntly: the box has to be big enough for the cat to stand on all fours and turn around, and cats generally prefer larger, more open boxes. Owners of genuinely big cats should skip both and look at our picks built for large cats.

Capacity: Where the 4 Pulls Ahead

The EVO supports up to two cats weighing 3 to 19 lb. The Litter-Robot 4 supports up to four cats weighing 3 to 25 lb. Whisker states both limits plainly on the Litter-Robot EVO and Litter-Robot 4 product pages, and they’re the cleanest decision line in this comparison.

The 19 lb ceiling deserves attention because plenty of ordinary house cats live near it. A chunky domestic shorthair, a Ragdoll, a British Shorthair, most Maine Coons — these are not exotic cases. If your cat is 17 or 18 lb and still filling out, buying to the edge of the EVO’s range is a bad bet.

The two-cat ceiling is more about throughput than physics. Two cats sharing an EVO will have you emptying the drawer noticeably more often than one cat will, and the EVO only tells you when the drawer is full rather than tracking how full it’s getting. With three or more cats you want the 4’s larger drawer and its more granular monitoring — or a box designed specifically for the load, which we cover in our multi-cat automatic litter box guide.

Sensors, Accessories, and What EVO Gives Up

This is the part of the spec sheet that separates “compact version” from “cheaper version.”

LitterLevel sensing. The Litter-Robot 4 tracks how much clean litter remains and tells you before you’re running low. The EVO doesn’t have it. In day-to-day life this means you go back to eyeballing the litter bed, which is fine — it’s what everyone did before the feature existed — but it’s a genuine convenience gap.

Waste-level detail. The 4 reports how full the drawer is getting. The EVO notifies you when it’s full. Same information, later.

Night light. The 4 has an automatic LED night light. The EVO doesn’t. Small thing, but if the box lives in a dark hallway it’s one more reason a nervous cat hesitates at the entry.

Accessories. The Litter-Robot 4 works with Whisker’s LitterHopper (automatic litter refill) and Shield (litter containment). The EVO supports neither — the LitterHopper’s own product FAQ states it fits the Litter-Robot 4 only, not the EVO, the 5-series, or the 3. That’s a closed door on future upgrades, and it’s worth weighing if you’re the kind of buyer who adds accessories over time.

WasteID. Neither box has it. Urine-versus-feces detection is exclusive to the 5-series, so if that’s what you’re shopping for, neither of these is the answer — see our Litter-Robot 5 vs 5 Pro comparison instead.

Which to Buy

One cat, tight space, under 19 lb. The EVO. This is precisely the household Whisker designed it for, and nothing you give up — litter-level sensing, night light, accessory support — changes how well the box cleans. You can check current listings for the Litter-Robot EVO alongside other compact self-cleaning litter boxes.

Two cats or a big cat. The Litter-Robot 4. The extra weight headroom, the larger entryway, and the deeper globe all matter more as the cat gets bigger, and the drawer keeps up better with two.

You want the cheapest way into automatic scooping. Neither, necessarily. The EVO is Whisker’s entry price, but it’s still a premium-tier box against the wider market. Our roundup of cheaper Litter-Robot alternatives and our budget-tier picks cover what you actually give up further down the ladder — and our Litter-Robot 4 vs PetKit PuraMax 2 comparison is the closest cross-brand matchup to this one.

FAQ

Is the Litter-Robot EVO worth it over the Litter-Robot 4? For a single cat under 19 lb in a small space, yes — you save money and floor area without losing cleaning performance. For two or more cats, no. The 4’s larger drawer, higher weight ceiling, and litter-level sensing earn the difference quickly.

How many cats can use a Litter-Robot EVO? Up to two, per Whisker’s stated capacity. The 4 goes to four. Both figures assume you’re emptying the drawer on schedule.

Does the Litter-Robot EVO have WasteID? No. WasteID, which distinguishes urine from feces, is only on the Litter-Robot 5 and 5 Pro. Neither the EVO nor the 4 has it.

Does the EVO have a screen? Yes, and this is the one place it out-specs the Litter-Robot 4. The EVO has a full-color LCD display for setup prompts and status; the 4 has no display and relies on the Whisker app.

Can my 20-pound cat use the Litter-Robot EVO? No. The EVO’s stated range tops out at 19 lb. Go to the Litter-Robot 4, which is rated to 25 lb and has a taller globe and wider entry.

Does the Litter-Robot EVO work with the LitterHopper? No. LitterHopper and Shield are compatible with the Litter-Robot 4 but not the EVO. If accessory expansion matters to you, that’s an argument for the 4 on its own.

Conclusion

The EVO isn’t a lesser Litter-Robot so much as a narrower one. It cleans the way the rest of the line cleans, runs the same app, and carries the same trial and warranty — but it’s built for one cat in a small room, and Whisker drew the boundaries around that use case tightly. Stay inside them and it’s the smartest entry into the lineup. Cross any one of them — a second cat, a heavy cat, a wish for litter-level alerts or a LitterHopper down the road — and the Litter-Robot 4 stops being an upsell and starts being the correct box. Measure your space, weigh your cat, count your cats, and the answer picks itself.