Arris Surfboard S33 Review: Multi-Gig Cable Modem

The ARRIS SURFboard S33 occupies a sweet spot in the DOCSIS 3.1 modem market: it costs less than many competing multi-gig modems while including two Ethernet ports — a 2.5 Gbps and a 1 Gbps — a combination you won’t find on most rivals at the same price. If you’re paying a monthly rental fee on your cable company’s modem, the S33 will typically pay for itself in under a year. Run a WiFi speed test before and after the swap to see the real-world improvement.

Who the S33 Is For

The SURFboard S33 is built for cable internet subscribers — specifically those on Comcast Xfinity, Charter Spectrum, or Cox — who are on gigabit or multi-gig plans and want to stop paying modem rental fees. It is not compatible with AT&T, Verizon Fios, Google Fiber, or any fiber or DSL provider. The S33 is a modem only; it has no built-in WiFi radio, so you’ll need a separate router or mesh system. Pairing a standalone modem with a standalone router gives you the flexibility to upgrade each component independently as technology evolves.

If you’re on a plan below 500 Mbps and want to save money, a less expensive DOCSIS 3.0 modem will do the job. But if you’re on a gigabit plan — or plan to upgrade to one — the S33 is the right foundation.

DOCSIS 3.1: The Standard That Matters

DOCSIS 3.1 is the current standard for cable modems, supporting downstream speeds up to 10 Gbps and upstream up to 1 Gbps in full deployments. The S33 ships with:

• 32 downstream × 8 upstream DOCSIS 3.0 bonded channels
• 2 downstream × 2 upstream OFDM DOCSIS 3.1 channels
• Maximum theoretical downstream speed of approximately 3.5 Gbps

In practice, your ISP’s head-end equipment — not the modem — determines the speed ceiling. On Xfinity’s 1.2 Gbps plan or Cox Gigablast, the S33 comfortably delivers the full plan speed without being the bottleneck. For a deeper look at what these specifications mean day-to-day, see our guide on DOCSIS 3.0 vs DOCSIS 3.1.

The Dual Ethernet Advantage

The headline feature that differentiates the S33 from most competing DOCSIS 3.1 modems is its dual Ethernet output: a 2.5 Gbps Multi-Gig port and a standard 1 Gbps port on the same device.

The 2.5 Gbps port is the primary connection for your router. If your router has a 2.5G WAN port — which most mid-range and flagship routers released since 2023 do — the S33 can pass the full throughput of Xfinity’s 1.2 Gbps and 2 Gbps tiers without the 940 Mbps ceiling that standard Gigabit Ethernet imposes. This is a meaningful advantage over DOCSIS 3.1 modems like the Arris SB8200, which ship with only a single 1 Gbps port.

The second 1 Gbps port can connect a second device directly — a desktop PC, a NAS, or a second router in a dual-WAN configuration. Note that the S33 does not support WAN link aggregation across both ports, so you cannot bond them to deliver a combined 3.5 Gbps connection. Each port carries its own independent traffic up to its rated speed.

ISP Approval and Compatibility

ISP approval is the non-negotiable criterion when buying any cable modem. An unapproved device may be blocked from activating, or may activate but suffer chronic disconnects. The SURFboard S33 is CableLabs certified and has been officially qualified by:

• Comcast Xfinity — all speed tiers including 1.2 Gbps and multi-gig plans
• Charter Spectrum — all tiers including Spectrum Internet Gig
• Cox Communications — including Gigablast

Always verify against your ISP’s current approved modem list before purchasing, as ISPs update their lists periodically.

Design and Build Quality

ARRIS gave the S33 a curvier, more contemporary look compared to older Surfboard models — rounded corners and a compact footprint of 5.14 × 1.8 × 4.74 inches. It weighs under a pound and fits easily on a shelf, desk, or entertainment unit without dominating the space. The design deliberately complements ARRIS’s WiFi 6 router lineup for a unified aesthetic if you opt for an all-ARRIS setup.

Front-panel LEDs indicate power, downstream, upstream, and online status. No software or companion app is required — plug it in, connect the coax, call your ISP to provision the MAC address, and you’re done. The physical setup takes under five minutes.

One caveat: the S33 runs noticeably warm under sustained load. This is passive cooling by design — no fan noise — but you should keep it in a ventilated location rather than in an enclosed cabinet. Extended operation in a tight space can cause the unit to throttle performance or reboot unexpectedly.

Performance

Connected to a Xfinity 1.2 Gbps plan and a router with a 2.5G WAN port, the S33 consistently delivers 1,100–1,180 Mbps downstream measured at the router’s WAN interface — well above the 940 Mbps ceiling of a standard Gigabit Ethernet modem. Upstream speeds track the ISP’s allocation; on Xfinity that’s typically 35–42 Mbps (asymmetric by design on DOCSIS).

Latency to the first hop averages 5–9 ms in typical DOCSIS 3.1 deployments — low enough that the modem itself won’t be the source of gaming lag or video call jitter. For context on what these latency numbers mean for your use case, see our guide on what is a good ping speed.

Long-Term Reliability

User reports across Amazon and Best Buy consistently praise the S33’s long-term stability. Unlike ISP-supplied modems that often need periodic reboots to restore full speed, the S33 tends to run for weeks without intervention. DOCSIS 3.1’s improved channel management and the modem’s solid firmware history contribute to this reliability.

Rental Payback Period

At $199.99 and a typical ISP modem rental of $15–$20 per month, the S33 pays for itself in roughly 10–13 months. Over a three-year ownership period, you save $340–$520 compared to renting — well worth it for any household planning to stay on cable internet. ARRIS backs the S33 with a two-year warranty.

How It Compares

The S33’s closest competitors are the Motorola MB8611 and the Netgear CM2000. The MB8611 is nearly identical in price and DOCSIS performance but carries only a single 2.5G Ethernet port — the S33’s dual-port design is a genuine advantage if you want to connect two devices directly to the modem. The Netgear CM2000 also offers dual ports but typically costs $20–$30 more and has narrower ISP approval. For most buyers, the S33 is the better value.

If your internet plan is below 500 Mbps and you don’t anticipate upgrading, a DOCSIS 3.0 modem will serve you adequately at a lower upfront cost. But for anyone on or planning for gigabit service, DOCSIS 3.1 is the right investment.

Verdict

The ARRIS SURFboard S33 is a well-rounded DOCSIS 3.1 modem that earns its place at the top of the cable modem shortlist for Xfinity, Spectrum, and Cox subscribers. The dual Ethernet outputs — 2.5 Gbps and 1 Gbps — set it apart from single-port rivals at the same price, the CableLabs certification ensures ISP compatibility, and the payback math is straightforward: buy it once, stop paying rental fees, and put the savings toward a better router. Pair it with a WiFi 6 or WiFi 7 router, run a speed test after setup, and enjoy the full throughput your internet plan delivers.