Updated: July 2026 | Read time: 8 min
Key Takeaways
- Every current Xfinity tier runs best on a DOCSIS 3.1 modem from Xfinity's approved device list. DOCSIS 3.0 units still activate on entry plans, but Xfinity has been steadily retiring them.
- Mid-split is the upstream expansion behind Xfinity's Next Gen plans, and Xfinity publishes a separate, much shorter list of devices rated for it. Models on that list are rated for roughly 419 to 486 Mbps upstream, not the 10 to 35 Mbps typical of older cable plans.
- The Arris S33 is marked Recommended by Xfinity and handles up to 2.33 Gbps down, but it is not on the Next Gen list. For enhanced uploads, look at the Arris S34, Netgear CM3000 or CM2500, Hitron CODA56, Ubiquiti UCI, or an Arris G-series gateway.
- Choose a 2.5 GbE modem for any plan at or above 1 Gbps, and an eMTA (voice) model only if you keep Xfinity Voice.
- Refurbished and new modems activate identically. Xfinity checks the model against its list and the MAC address against its records, so the model, a clean registration history, and a warranty are what decide the outcome.
If you are on Xfinity and want faster uploads for video calls, gaming, and backups without paying a rental fee every month, the move is a DOCSIS 3.1 modem that lines up with Xfinity's mid-split upgrades. Below we translate Xfinity's current compatibility documents into picks by plan, explain the one list most buyers miss, and give you a provisioning checklist.
Mid-split in plain English
Cable networks split their spectrum between download and upload traffic, and historically the upstream slice was tiny: about 5 to 42 MHz, which is why cable uploads sat around 10 to 35 Mbps for years. Mid-split widens that upstream slice to roughly 85 MHz, and the difference shows up immediately in anything that pushes data out of your house: cloud backups, live streams, large file transfers, and the outbound side of a video call.
Xfinity markets the plans running on upgraded nodes as Next Gen tiers. It is also deploying DOCSIS 4.0 for symmetrical multi-gig service in select markets, but that footprint is still growing. For most households, DOCSIS 3.1 plus mid-split is where the value sits today.
The Next Gen list is not the same as the compatible list
This is the part that costs people upload speed. Xfinity's compatible devices document contains three separate tables: a general Recommended list, a full compatibility list, and a short Next Gen Speed Tier list. A modem can sit on the first two and still be absent from the third, which means it activates fine, delivers its rated download speed, and never gives you the enhanced uploads you are paying for.
These are the devices Xfinity rates for Next Gen upstream, with the wired speeds it publishes for each:
| Model | Built-in Wi-Fi | Max wired download | Max wired upload |
|---|---|---|---|
| Arris S34 | No | Up to 2.32 Gbps | Up to 444 Mbps |
| Arris G20 | Yes | Up to 934 Mbps | Up to 447 Mbps |
| Arris G34 | Yes | Up to 934 Mbps | Up to 472 Mbps |
| Arris G36 | Yes | Up to 2.32 Gbps | Up to 419 Mbps |
| Arris G54 | Yes | Up to 2.34 Gbps | Up to 474 Mbps |
| Netgear CM2500 | No | Up to 936 Mbps | Up to 456 Mbps |
| Netgear CM3000 | No | Up to 2.33 Gbps | Up to 486 Mbps |
| Netgear CBR750 | Yes | Up to 924 Mbps | Up to 471 Mbps |
| Hitron CODA | No | Up to 934 Mbps | Up to 456 Mbps |
| Hitron CODA56 | No | Up to 2.33 Gbps | Up to 455 Mbps |
| Ubiquiti UCI | No | Up to 2.33 Gbps | Up to 474 Mbps |
If enhanced uploads are not offered at your address yet, this list does not constrain you. Any DOCSIS 3.1 modem on the compatible list will serve your plan, and a Next Gen model simply means you are ready when the upgrade reaches your node.
Best Xfinity modems by plan
Entry and mid tiers (roughly 400 to 600 Mbps)
- Arris SBG8300 (DOCSIS 3.1 gateway with Wi-Fi): marked Recommended by Xfinity and the simplest one-box option for a smaller home.
- Motorola MB7621 (DOCSIS 3.0): still compatible and inexpensive for sub-gigabit plans. Worth knowing that Xfinity has been removing DOCSIS 3.0 models from its list over time, so 3.1 is the safer spend if you plan to keep the unit for years.
Gigabit plans (800 Mbps to 1.2 Gbps)
- Arris S33 (DOCSIS 3.1, 2.5 GbE): compact, quiet, Recommended on Xfinity's general list, and rated up to 2.33 Gbps down. Excellent on standard gigabit plans.
- Motorola MB8611 (DOCSIS 3.1, 2.5 GbE): a popular gigabit workhorse with the same 2.33 Gbps ceiling.
- Netgear CM1100 (DOCSIS 3.1): Recommended in Xfinity's document, with link aggregation on its two gigabit ports.
If your plan includes enhanced uploads
Here the popular pick and the correct pick separate. The S33 is a strong modem, but it does not appear on the Next Gen table, so it is not rated for the wider upstream. If you are paying for the faster uploads, choose from the Next Gen list instead. The Arris S34 is the closest equivalent to the S33 in size and price, and the Netgear CM3000 currently carries the highest published upstream figure at 486 Mbps. The Hitron CODA56 is the value option in the group and appears on both the Recommended and Next Gen tables. All three are standalone modems, so pair them with your own router.
Multi-gig downloads (1.2 Gbps and up)
- Netgear CM2000 or CM3000 (DOCSIS 3.1, 2.5 GbE): both rated to 2.33 Gbps, with the CM3000 also on the Next Gen list.
- Hitron CODA56 (DOCSIS 3.1, 2.5 GbE): Recommended, multi-gig capable, and usually the cheaper way to get there.
Above 1 Gbps, the 2.5 GbE port stops being a nice extra. A single gigabit port caps you below your plan no matter how capable the modem is.
If you keep Xfinity Voice
- Netgear CM2050V (DOCSIS 3.1, 2.5 GbE, telephony): Recommended, and the fastest voice-capable option on the list.
- Arris T25 (DOCSIS 3.1, telephony): the proven eMTA pick for a voice bundle on a gigabit plan.
Standard modems will not carry Xfinity Voice, so this is the one situation where the model choice is made for you. If you do not have home phone service, skip telephony models and save the money.
Modem or gateway? Xfinity's list includes combo gateways such as the Netgear CAX80 and CBR750 alongside standalone modems, and both provision the same way. A separate modem and router costs a little more up front but lets you replace the Wi-Fi side on its own schedule, which is where most upgrades actually happen. Browse Xfinity compatible modems or the full DOCSIS 3.1 collection.
Refurbished or new: what actually decides whether a modem works
Xfinity provisions a modem on two facts: the model, which has to appear on the compatible device list, and the MAC address, which cannot still be registered to another account. Nothing in that process looks at the box, the purchase date, or whether the unit had a previous owner. A tested refurbished modem on the list activates exactly the way a sealed one does.
Xfinity's device document does encourage buying new, and the reason it gives is manufacturer support for performance and security updates. That reasoning applies far more to routers than to cable modems. On a DOCSIS network, modem firmware is pushed by the operator rather than installed by the owner, so your modem loads the same image Comcast serves to every other unit of that model on the network. Where the hardware came from does not change which firmware it runs.
What does matter when you buy used or refurbished comes down to three things:
- The model. It needs to be on the current compatible list, and on the Next Gen list if enhanced uploads are the point.
- A clean registration history. The MAC should not still be tied to a previous subscriber. Sellers who process returns properly clear this before a unit ships, which is the practical difference between a dealer and a random marketplace listing.
- Coverage after the sale. A warranty, a real return window, and someone to talk to if activation stalls on the first try.
Buying refurbished also changes the math on the whole exercise. Owning your equipment is about escaping the rental line on your bill, and a refurbished DOCSIS 3.1 modem reaches that break-even point in a fraction of the time a new one does. Retired networking gear that still has years of service in it is also the least wasteful option available, which is the reason this store exists.
How we handle it: every modem and router we sell is Grade A refurbished and hand tested in the United States, backed by a 90-day full-coverage warranty, free returns within 30 days, and US-based support Monday through Friday. Compatible modems are covered by our activation guarantee. We have been rehoming networking equipment since 2015 and shipped more than 10,000 devices last year. See our Xfinity compatible modems or read more about us.
DOCSIS 4.0 vs DOCSIS 3.1: should you wait?
If symmetrical multi-gig service is already live at your address, that is the endgame and worth buying into. Everywhere else, waiting costs you real upload speed today in exchange for a plan you cannot order yet. Retail DOCSIS 4.0 hardware is still thin, priced at a premium, and pointless on a node that has not been upgraded. A DOCSIS 3.1 modem on the Next Gen list captures the upload gains that are actually available now, and modems are cheap enough that replacing one in a few years is not a painful decision.
Activation checklist
- Check compatibility for your address first. Xfinity's My Device Info tool confirms what your specific line supports, and the lists change.
- Record the HFC MAC and serial number from the label before the modem goes behind furniture.
- Connect coax and power, then run an Ethernet cable from the modem to your router's WAN port. Give it two to five minutes for the lights to settle.
- Activate through the Xfinity app or at xfinity.com/activate. Chat and phone support can do it as well if the automated path stalls.
- Reboot the router once you are online, then run an upload and download test plus a quick latency check.
- If speeds look capped, ask support to refresh the modem and confirm your provisioned tier, then check that OFDM and OFDMA channels show as locked on the modem's status page. Those are the DOCSIS 3.1 profiles that carry mid-split upstream.
FAQs
Will a refurbished modem activate on Xfinity?
Yes. Activation depends on the model appearing on Xfinity's approved list and the MAC address not being registered to another account. Condition and purchase history are not part of the check, which is why a properly cleared and tested unit provisions like any other.
Is the Arris S33 a good choice for Xfinity?
For standard plans, yes, and Xfinity marks it Recommended. For Next Gen plans with enhanced uploads, no, because it is not on that separate list. The S34 is the direct alternative that is.
Do I need a telephony modem if I do not use Xfinity Voice?
No. A data-only DOCSIS 3.1 model is cheaper and simpler, and voice hardware brings nothing to a data-only plan.
Does every modem include Wi-Fi?
No. A modem is the bridge to the cable network. Gateways combine a modem and a router in one housing. Xfinity supports both, so if you buy a standalone modem, plan on a router to handle wireless.
Will my own modem be slower than the rented gateway?
No. Your speed tier is provisioned to your account, not to the hardware. A current DOCSIS 3.1 modem on the correct list delivers the plan you pay for, and standalone modems often run cooler than combo units under sustained load.
What about the old Intel Puma 6 latency problem?
It affected a specific generation of DOCSIS 3.0 chipsets and produced spiky latency under load. Any of the DOCSIS 3.1 models above avoids it.
Related reading
- Xfinity approved modem list
- Best DOCSIS 3.1 modems
- Arris S33 vs Motorola MB8611 vs Hitron CODA56
- How long do modems last?
Device specifications and list placements above are drawn from Xfinity's published compatible devices document, last updated March 26, 2025. Xfinity refreshes its recommendations quarterly, so confirm your model against My Device Info before buying.
