CompareInternet is independent and reader-supported. When you buy through links on this page we may earn a commission from Amazon or eBay at no extra cost to you. We don't accept payment for placement, and we don't publish made-up speeds, test scores or prices — tiers ($ to $$$) show relative cost only. Provider plans and pricing change often; always confirm on the provider's site.
DOCSIS (Data Over Cable Service Interface Specification) is the standard that lets cable internet run over coax. DOCSIS 3.1 powers most cable internet today, including gigabit plans. DOCSIS 4.0 is the next generation, designed above all to close the gap with fiber on upload speeds and multi-gig service.
Cable ISPs such as Comcast (Xfinity) and Charter (Spectrum) have been upgrading their networks for DOCSIS 4.0 in stages, market by market. Here's what changes, and what it means for your modem and your plan.
Head-to-head
| DOCSIS 3.1 | DOCSIS 4.0 | |
|---|---|---|
| Status | Mainstream; used by most cable plans | Rolling out in select markets |
| Download | Gigabit and multi-gig tiers on upgraded networks | Designed for substantially faster multi-gig downloads |
| Upload | Typically a small fraction of download | Designed for much faster, closer-to-symmetrical uploads |
| Latency | Good; supports low-latency features on some networks | Designed with further latency improvements |
| Modems | Widely available at retail | Mostly ISP-provided gateways so far; retail options emerging |
The big change: upload
For most households, download speeds on DOCSIS 3.1 are already plenty. The weak spot has been upload, which matters for video calls, cloud backup, content creation and cameras. DOCSIS 4.0 dedicates far more of the cable spectrum to upstream traffic, so ISPs can offer much faster uploads, and in some tiers speeds that approach fiber's symmetry. See why upload speed matters.
Do you need a new modem?
Not unless you're moving to a DOCSIS 4.0 plan. A DOCSIS 3.1 modem works on 3.1 plans, including on upgraded networks. To get DOCSIS 4.0 speeds, you'll need a 4.0-capable modem, and for now that's usually the ISP's own gateway. When retail DOCSIS 4.0 modems appear on your ISP's approved list, they'll become an option for people who want to stop renting.
If you're buying a modem today for a current plan, get a DOCSIS 3.1 model with a 2.5GbE port. See best cable modems.
DOCSIS 4.0 vs fiber
DOCSIS 4.0 narrows the gap, but fiber still has structural advantages: symmetrical speeds are standard on most fiber plans, latency is typically very low and consistent, and the technology has enormous headroom for future upgrades. Where both are available, fiber is usually the better long-term choice. Where fiber isn't available, DOCSIS 4.0 is a big step up for cable customers. Compare in fiber vs cable.
How to know if DOCSIS 4.0 is in your area
Check your cable provider's site with your exact address. Providers often market DOCSIS 4.0 plans under new names emphasizing multi-gig or symmetrical-style speeds. You can also ask support directly, or watch local news for network upgrade announcements. Our address availability guide helps you see every option at your address.
What about latency?
Cable networks have also been adding low-latency features, such as Low Latency DOCSIS (LLD), which can reduce delay for latency-sensitive traffic like gaming and video calls when your ISP, modem and applications support it. These features aren't exclusive to DOCSIS 4.0, and availability varies by provider. For latency problems at home, bufferbloat is still the most common culprit, and a router with SQM is the fix. See bufferbloat explained.
Should you wait for DOCSIS 4.0?
If your current plan works, there's no reason to wait or switch. If you're shopping for service now and fiber isn't available, choose the best DOCSIS 3.1 plan for your needs today, and avoid long contracts so you can move to a 4.0 plan when it arrives. If upload is your pain point and a fiber provider is coming soon, it may be worth staying flexible for that instead.
The verdict
If you're happy with your current cable plan, you don't need to do anything. DOCSIS 3.1 remains excellent. If upload speed limits you and fiber isn't available, watch for DOCSIS 4.0 plans in your area. When they arrive, they're one of the biggest cable upgrades in years.
The best DOCSIS 3.1 modems to buy today
1. ARRIS SURFboard S33
$$Best for: Multi-gig DOCSIS 3.1 plans
DOCSIS 3.1 with a 2.5GbE port and broad ISP approval, which makes it a future-friendly choice until DOCSIS 4.0 retail options mature.
What we like
- 2.5GbE port
- Widely approved
Watch out for
- Not DOCSIS 4.0
2. Motorola MB8611
$$Best for: Gigabit-plus plans
A comparable DOCSIS 3.1 modem with 2.5GbE. Buy whichever your ISP approves and costs less.
What we like
- 2.5GbE port
- Good track record
Watch out for
- Single Ethernet port
3. ARRIS SURFboard SB8200
$Best for: Gigabit-and-under plans
A proven, affordable DOCSIS 3.1 modem for plans up to about a gigabit.
What we like
- Affordable 3.1 modem
- Two 1GbE ports
Watch out for
- Link aggregation needed beyond 1Gbps
Frequently asked questions
What's the main difference between DOCSIS 3.1 and 4.0?
DOCSIS 4.0 enables much faster uploads and faster multi-gig downloads. Upload is the biggest change for most users.
Should I buy a DOCSIS 4.0 modem now?
Only if your ISP offers a 4.0 plan in your area and approves a retail 4.0 modem. Otherwise buy DOCSIS 3.1.
Will my DOCSIS 3.1 modem stop working?
No. DOCSIS 3.1 modems continue to work on 3.1 plans, including on upgraded networks.
Is DOCSIS 4.0 as good as fiber?
It narrows the gap, especially on upload. Fiber still typically offers symmetrical speeds, very low latency and more headroom.
Which ISPs offer DOCSIS 4.0?
Major cable providers, including Comcast and Charter, have been rolling out DOCSIS 4.0 in stages. Check your address for availability.