Javascript has two differences that contribute here: * First, it runs the callee synchronously until the first await, which can fire off network requests, etc.

Javascript has two differences that contribute here: * First, it runs the callee synchronously until the first await, which can fire off network requests, etc. * Second, continuations are pushed onto queues immediately- the microtask queue that runs when the current event handler returns, for example. Rust does neither of these things: * Calling an async function constructs its stack frame without running any of its body. * Continuations are not managed individually; instead an entire stack of async function frames (aka Futures) is scheduled as a unit (aka a "task"). So if you just write async functions and await them, things behave much more like thread APIs- futures start running when you pass a top-level future to a "spawn" API, and futures run concurrently when you combine them with "join"/"select"/etc APIs.