DOCSIS 3.0 vs. 3.1 vs. 4.0: Which Cable Modem Do You Need?

If you have cable internet and are buying your own modem, a DOCSIS 3.1 model is the safe choice for most plans sold today. DOCSIS 3.0 tops out at 1 Gbps down, and DOCSIS 4.0 only matters where your provider has upgraded its network. Before you buy anything, check your provider’s approved device list for your speed tier.

This is a research-based buying guide built from CableLabs, Netgear and Comcast documentation. We have not tested cable modems, and we don’t quote prices.

What is DOCSIS?

DOCSIS (Data Over Cable Service Interface Specification) is the standard cable modems use to talk to a cable provider’s network. It’s developed by CableLabs, the cable industry’s research group. It applies only to cable internet; fiber and 5G home internet use different equipment.

The version number tells you the maximum speeds a modem can handle.

DOCSIS 3.0 vs. 3.1 vs. 4.0 at a glance

Netgear notes these are “maximum speeds and are not guaranteed.” Your plan, your provider’s network and your home wiring set the real limits. Netgear’s own DOCSIS 3.1 explainer gives the 3.1 upload maximum as 2 Gbps in one place and 1 Gbps in another; we use the 1 Gbps figure from its support article.

The big change in DOCSIS 4.0 is upload speed. Comcast says its DOCSIS 4.0 approach uses a technology called Full Duplex to raise upstream speeds without reducing downstream speeds.

Which one do you need?

Netgear says DOCSIS 3.1 is “backward compatible with DOCSIS 3.0,” works “just fine on lower-speed plans,” and that “in some cases your ISP may recommend or even require” a DOCSIS 3.1 modem. That makes 3.1 the safer buy unless your provider says otherwise.

Check your provider’s list first

A cable modem has to be approved by your provider and support your speed tier, or it may not work at all. Xfinity puts it this way: “Before you buy a device, make sure it works with Xfinity services and supports your internet speed.” It points customers to its My Device Info lookup, where you can sign in or enter your address to see compatible devices. For Gigabit plans, Xfinity says the device “must support Gigabit speeds.”

Other cable providers publish their own lists. Search your provider’s support site for “approved modems” or “compatible devices.”

Owning your modem also makes you responsible for it. Xfinity lists keeping the device updated and secure, using equipment that supports your speed, and troubleshooting as the owner’s job. Our guide to buying your own router vs. using your provider’s covers equipment fees and the trade-offs.

Is DOCSIS 4.0 available yet?

In some places. Comcast announced its first DOCSIS 4.0 deployment on October 12, 2023, starting in select neighborhoods of Colorado Springs, with parts of Atlanta and Philadelphia to follow. In March 2026, Light Reading reported Comcast saying the service reaches “millions” of homes, out of a network that passes about 65 million homes and businesses.

So most cable customers can’t use DOCSIS 4.0 yet. Buy a 4.0 modem only if your provider offers 4.0 service at your address and lists the modem as supported.

Modem, router or gateway?

A modem connects to the provider’s line. A router creates your home network and Wi-Fi. A gateway combines both. If you buy a standalone modem, you’ll also need a router or mesh system. If your plan is faster than 1 Gbps, check that both have multi-gig ports; see do you need a multi-gig router. If you keep the provider’s gateway and add your own router, our bridge mode and double NAT guide explains the setup.

Not sure you need a faster plan at all? See how much internet speed you need and fiber vs. cable vs. 5G home internet.

Fact-check notes

Bottom line

Buy a DOCSIS 3.1 modem that your provider approves for your speed tier. Skip DOCSIS 3.0 unless your plan is slow and your provider still supports it, and wait on DOCSIS 4.0 until your provider offers it at your address.