How fast do you want it?

In March I wrote about JSSE, a JavaScript engine an agent built from scratch in Rust. It passed 100% of test262 non-staging tests. It was also slow. Intentionally so. The "What's Next" section of that post named bytecode compilation as the obvious next step, with 10x to 100x to be gained. This post is not about bytecode. Seven weeks later, the same test262 suite runs 4.73x faster on the same machine, against the same source checkout, with the same toolchain. JetStream geometric mean speedup is 1.92x across 19 comparable workloads. Seven JetStream workloads that previously timed out or errored now run clean. The full numbers and the methodology are in docs/perf/2026-05-07/benchmark-report.md. What changed is not the architecture. JSSE is still a tree-walking interpreter. No bytecode VM, no inline caches, no hidden classes. The agent and I attacked the constant factors of the existing engine, one issue at a time. The Dial The previous post promised bytecode. I didn't do bytecode this…