The agent runtime is the new browser layer, and your website is going to be evaluated against the runtime, not against any individual model. That’s a shift web professionals have not yet made. The conversation is still framed around models. Which model writes better? Which one cites more accurately? Which one’s API is cheaper this month? The model conversation is loud because new models ship every few weeks, and every release is theatrical. The interesting story is the one underneath it. The foundation is being rebuilt. This week made it impossible to ignore. The Runtime Stack Shipped In April On April 15, Cloudflare shipped Project Think , a new Agents SDK built around durable execution with crash recovery and checkpointing, sub-agents that run as isolated children, persistent sessions with tree-structured messages, and sandboxed code execution running on Dynamic Workers.…