Model differences
Ninja DCT801BK vs DCT871: two zones, one probe difference
DCT801BK and DCT871 share a recognizable idea: two oven compartments can run separately at different temperatures and times, with Smart Finish coordinating when they end. The choice between them is more specific than “standard versus Pro.” The DCT871 page lists a Pro Cook Thermometer and describes Auto Temp Detect; the DCT801BK box list does not include a probe. The DCT871 page also lists a substantially larger body and weight. Compare the exact model code, the food routine you expect to use, and the counter before deciding.
What the models share
Both product pages describe separate top and lower cooking zones, QuartzHeat in the upper oven, and lower-zone 450°F surround-airflow Air Fry cooking. The manufacturer lists the same 12 programs across each appliance: Air Fry, Air Roast, Bagel, Broil, Bake, Toast, Whole Roast, Reheat, Max Crisp, Pizza, Convection Bake and Keep Warm. Both pages describe using one oven alone or cooking two foods at once with different time/temperature settings. That makes this family worth considering for households that often prepare a main and side, or a toast/snack job alongside a separate meal.
The mode count is not a per-chamber matrix. The official product summaries do not say that every function is available in both compartments, so look at the Quick Start Guide for the exact mode and oven you plan to use. Neither page's list includes Dehydrate. No app-connected cooking controls are documented on these exact US pages. Neither one publishes a cubic-foot capacity or pizza diameter. “XL” and an Air Fry label do not answer whether a particular casserole, pan or pizza fits.
DCT801BK: two zones without the listed probe
The Onyx DCT801BK page lists 18.7 in L x 17.2 in W x 13.98 in H and 25.35 lb. The exact in-box list names two sheet pans, two wire racks, one Air Fry Basket, one Crumb Tray, a Quick Start Guide and a 15-recipe guide. There is no Pro Cook thermometer in that list. If your usual cooking is two straightforward jobs at separate settings, and an internal probe is not essential, the DCT801BK preserves the central two-zone workflow without the DCT871 probe package. See the DCT801BK review for its precise tradeoffs.
DCT871: add a probe, then make room
The silver DCT871 is listed at 21.42 in L x 19.76 in W x 15.94 in H and 36.24 lb. Its in-box list adds the Pro Cook Thermometer. Ninja separately describes the system as monitoring food temperature toward a rare-to-well-done target. That is most compelling for the household that expects to use probe-guided cooking, not as a feature to pay for on the assumption it improves toast or every Air Fry load. Follow the included model guide for the foods and functions supported by the probe; the product summary is not the compatibility manual. The page gives separate examples of a 4.5-lb chicken or six toast slices, not a guarantee that any particular pan or food arrangement fits. See the DCT871 review.
DCT821: another exact model, not a DCT801 finish
The DCT821 Stainless product page describes two independently controlled ovens, Smart Finish, QuartzHeat in the top and Air Fry in the lower zone. It names Air Fry, Air Roast, Bagel, Broil, Bake, Toast, Whole Roast, Reheat, Max Crisp, Pizza, Convection Bake and Keep Warm across the appliance. Its public summary does not provide a mode-by-zone chart, so check the Quick Start Guide for the precise chamber/preset pairing you intend to use. The in-box list names two sheet pans, two wire racks, an Air Fry Basket, Crumb Tray and two guides, but no Pro Cook Thermometer.
DCT821 and DCT801BK have matching published body measurements and weight, but the exact DCT821 rendering shows a different numeric-display control face from the DCT801BK/BL/SD images. Ninja identifies DCT821 separately; do not select it as a finish variant just because the high-level cooking claims overlap. The product details do not explain whether the visible panel change alters its control sequence, and the DCT800-series operating guide remains a useful next check. Read the DCT821 review alongside the DCT801BK review when comparing the exact panel and package.
Compare the alternatives by layout, not family name
The Double Stack DCT601 and probe-equipped DCT651 are related two-zone Ninja ovens with a different layout and their own accessory set; the DCT601 versus DCT651 guide explains that distinction. The DCT651 is another probe-equipped two-zone choice, while DCT871 combines the probe with the Double Oven Pro configuration. The Prestige Pro XL DT551 is a probe-equipped alternative too, but its four rack positions share a single cavity rather than scheduling independent upper and lower ovens. Open the Prestige XL comparison if separate zones are not essential.
Every published dimension here is body-only. In the exact product-page axes, DCT801BK's W is 17.2 in and DCT871's W is 19.76 in; each listing also gives a longer L dimension. Verify the exact SKU and all three axes, then add model-specific operating clearance, door swing, outlet access and room to lift hot pans. Do not compare only front width or assume the related models share dimensions. Both are rated 1,800 W, 120 V and 15 A, with one-year limited warranties shown on the respective pages.
There is no performance ranking in this comparison. Actual cooking accuracy, timing, noise, toast shade and durability were not measured. The short choice is practical: DCT801BK if separate zones and Air Fry are the priority but the probe is not; DCT871 if probe-guided cooking is worth its larger listed body; DCT651 if a different two-zone layout and probe are attractive; DT551 if you want a single-cavity oven with a probe instead of two scheduled chambers.