DOCSIS 3.1 vs 3.0

DOCSIS is the standard your cable modem speaks. 3.1 is the current mainstream version and what most gigabit-and-up tiers require; 3.0 is the older one that many ISPs still accept on lower tiers. If your ISP publishes a minimum version, that line decides — it's quoted verbatim on your ISP's page here.

The practical rule

Buying today for anything but the cheapest tiers, 3.1 is the safe default: it's backward-compatible, ISPs are steadily retiring 3.0 devices from their lists, and the price gap has narrowed. Where an ISP's own list still includes 3.0 devices, they're typically capped to lower speed tiers — the per-device speed caps some ISPs publish are quoted on their pages.

What DOCSIS does not fix

Wi-Fi. A modem's DOCSIS version sets the wired ceiling from the wall; slow Wi-Fi in a far bedroom is a router problem. If your speeds are fine next to the modem and poor elsewhere, see modem vs gateway — the fix is on the router side.