Short answer: DOCSIS 4.0 mainly raises cable internet’s upload ceiling, from 1 Gbps to 6 Gbps according to CableLabs, which develops the standard. That makes symmetrical multi-gig plans possible over cable. It only matters if your provider offers DOCSIS 4.0 service where you live and you want such a plan. Otherwise a current DOCSIS 3.1 modem is still the right buy, and that’s what’s on retail shelves.

Side by side

DOCSIS 3.1 DOCSIS 4.0
Downstream capacity Up to 10 Gbps Up to 10 Gbps
Upstream capacity Up to 1 Gbps Up to 6 Gbps
What it enables Gigabit and multi-gig download plans Symmetrical multi-gig plans
Retail modems Widely available None in NETGEAR’s line as of 8 October 2026

Capacities are CableLabs’ specification figures; CableLabs notes that real networks vary.

What actually changes: upload

Both versions top out at about the same download capacity. The difference is the other direction: DOCSIS 4.0’s upload ceiling is six times DOCSIS 3.1’s. CableLabs describes how it gets there: full duplex operation (sending and receiving on the same part of the cable spectrum), and extended spectrum up to 1.8 GHz.

Can you buy a DOCSIS 4.0 modem?

Not easily, yet. As of 8 October 2026, NETGEAR’s retail cable modem line was DOCSIS 3.1 only, its top models being the CM3000 and CM2500. Cable providers decide which modems work on their networks: Xfinity, for example, requires an owned modem to work with Xfinity and support your plan’s speed. For a DOCSIS 4.0 plan, expect to use the equipment your provider specifies, at least until retail models reach its approved list.

Will my DOCSIS 3.1 modem stop working?

Not because DOCSIS 4.0 exists. But providers do retire older equipment over time; Xfinity, for instance, won’t install or activate devices it has declared end-of-life. A current DOCSIS 3.1 model, the newest generation in NETGEAR’s retail line, gives you the most time. Check your provider’s list before buying any modem.

Which DOCSIS version does your modem have?

Find the model number, then look the model up on the maker’s website. If you bought a NETGEAR modem and still have the box, NETGEAR says the model number is on the box’s side panel, in the Package Contents section, in parentheses after the product name. If your provider supplied the modem, check the provider’s equipment or support pages for the model instead. A maker’s product page for the model should state its DOCSIS version: NETGEAR’s page for the CM2500, for example, describes it as a DOCSIS 3.1 cable modem. If yours is DOCSIS 3.0, the next section is for you; if it’s 3.1, “Which should you choose?” below covers whether it suits your plan.

Still on a DOCSIS 3.0 modem?

DOCSIS 3.1 is the generation before 4.0 and the successor to 3.0. CableLabs released it in 2013 and says it reaches up to 10 Gbps down and 1 Gbps up (the standard’s maximums; your plan sets your actual speed), uses Active Queue Management to significantly reduce delays, and makes modems much more energy efficient than DOCSIS 3.0 models. NETGEAR says its DOCSIS 3.1 CM2500 will work only as a DOCSIS 3.0 modem if your provider doesn’t offer DOCSIS 3.1, so you’d get 3.0 service until it does. Providers also retire old equipment. Xfinity, for one, describes end-of-life devices as outdated and unable to keep up with today’s faster speeds, and won’t install or activate them; it lets you look up your modem’s make and model in its My Device Info tool to see whether it’s end of life. On another provider, check its support pages for a similar list.

Which should you choose?