I just learned about the L4S protocols (Low Latency, Low Loss, Scalable Throughput).
Here are some articles on it.
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TLDR;
Where classic TCP relies on packet losses to detect congestion, L4S Prague uses a bit in the IP header as an explicit congestion signal. That bit is called Explicit Congestion Notification (ECN). Using ECN makes it possible to signal congestion early and often. A congestion signal can be sent before the queue begins to fill and without paying the costs of dropping packets. This is one of the major strengths of L4S. Early and frequent signals allow the sender to react less dramatically to congestion signals, so the transmission rate can be fine-tuned quicker and more accurately. This, in theory (and in testbeds), allows for both high throughput and low latency.
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