[neonsunset]

IL is always different since it's a high-level bytecode. The machine code output is different too. Now, with guarded devirtualization of lambdas, in many instances LINQ gets close to open-coded loops in performance, and it is very clever in selecting optimal internal iterator implementations, bypassing deep iterator nesting, having fast-paths for popular scenarios, etc. to achieve very good performance that can even outperform loops that are more naive, but unfortunately we're not there yet in terms of not having a baseline overhead like iterators in Rust. There is a selection of community libraries that achieve something close to this, however. I would say, LINQ performance today gets as close as it can to "it's no longer something to be worried about" for the vast majority of codebases.