For those who came in late L4S is a standard which ensures data packets spend as little time needlessly waiting in line as possible by reducing the need for queuing. To do this, it makes the latency feedback loop shorter; when congestion starts happening, L4S means your devices find out about it almost immediately and can start doing something to fix the problem. Usually, that means backing off slightly on how much data they're sending.

Big companies like Apple, Google, Comcast, Charter, Nvidia, Valve, Nokia, Ericsson, T-Mobile parent company Deutsche Telekom, and more have shown an in the new standard since it was finalised and it could be used in anger soon."

The specification paper on the Internet Engineering Task Force's website said the L4S standard adds an indicator to packets, which says whether they experienced congestion on their journey from one device to another. If they sail right on through, there's no problem, and nothing happens. But if they must wait in a queue for more than a specified amount of time, they get marked as having experienced congestion. That way, the devices can adjust immediately to keep the congestion from worsening and potentially eliminate it.

CableLabs technologist Greg White helped work on the standard. "This buffering delay typically has been hundreds of milliseconds to even thousands of milliseconds in some cases. Some of the earlier fixes to buffer bloat brought that down into the tens of milliseconds, but L4S brings that down to single-digit milliseconds."

White from CableLabs said there were 20 cable modems that support it today and that several ISPs like Comcast, Charter, and Virgin Media have participated in events meant to test how prerelease hardware and software work with L4S. Companies like Nokia, Vodafone, and Google have also attended, so there seems to be some interest. Apple put an even bigger spotlight on L4S at WWDC 2023 after including its beta support in iOS 16 and macOS Ventura.

Comcast has announced the industry's first L4S field trials in collaboration with Apple, Nvidia, and Valve. That way, content providers can mark their traffic (like Nvidia's GeForce Now game streaming), and customers in the trial markets with compatible hardware like the Xfinity 10G Gateway XB7 / XB8, Arris S33, or Netgear CM1000v2 gateway can experience it now.

A factor helping L4S is that it's broadly compatible with the current congestion control systems.