I almost want to liken this attitude to Lua's approach to stability: The general look of the language will remain the same, but some base-line things may change between releases. That's the impression I got from the OP. (Granted, Lua gets used in a far different environment than Rust, so people holding onto an older version for their own projects is not a big deal in Lua. I don't think Rust wants to engender that attitude for its use. I'm not sure, though; I haven't really used Rust nor spent any time in the community.)