When I started building MCP-powered agents and Claude Skills at Harness, I kept running into weird transport issues, connections dropping behind load balancers, SSE endpoints behaving differently across clients, tutorials that contradicted the actual spec. Turns out, MCP's transport layer had quietly gone through a major overhaul and most of the content out there hadn't caught up.

In this talk, I'll walk through MCP's transport journey, stdio for local tooling, the dual-endpoint SSE model that powered early remote servers, and the Streamable HTTP design that replaced it in the March 2025 spec update. More importantly, I'll explain why each shift happened: the scaling headaches SSE caused, the connection recovery gap, and the auth/CORS simplifications that Streamable HTTP unlocked.

I'll share code from actual migrations I've worked through, what breaks when you switch, what gets simpler, and the backward-compatibility gotchas that the docs don't warn you about. If you're building or maintaining MCP servers today, this should save you a few weekends of debugging.