Defining a function that takes a C-style variable argument list — the `printf` shape — has been a stable-Rust gap for years. 1.99 closes it: the `"C"` and `"C-unwind"` ABIs now let you write variadic functions directly, which matters most if you're writing a library that has to hand C code a callback it can call with a `va_list`. Alongside it, the raw-pointer layout question finally gets settled — `Layout::for_value_raw`, `mem::size_of_val_raw`, and `mem::align_of_val_raw` are stable, so you can ask a raw pointer for its size and alignment even when it points at an unsized type. The rest is the usual six-week batch, but a couple of pieces stand out. There's a new dedicated Cargo debug profile, a refreshed `Box::leak` doc that now steers you away from leaking-then-reclaiming (it interacts badly with current and future optimizations), and RISC-V moves up to Tier 2 on the back of LLVM 23. If you maintain FFI-heavy crates, the variadic stabilization is the one to read first; everything else can wait for the point releases.