Load-tests SSE endpoints at scale with k6 - measures concurrent-stream capacity, connection churn, and server memory pressure. Covers the HTTP/1.1 6-connection-per-origin browser ceiling vs HTTP/2 multiplexing, a custom k6 SSE client built on ReadableStream, and threshold gates for TTFB and data throughput. Use when validating whether a server can sustain N concurrent EventSource connections without connection starvation or memory growth.