Why is Cairo being evaluated as Kaspa's first smart-contract VM?

Cairo, developed by StarkWare, is being evaluated as the likely first VM to run Kaspa's vProgs because its Sierra bytecode format uniquely provides provable metering and safety. In a zero-knowledge execution environment, provable metering means the network can mathematically verify how much work a program performed — a critical safety property that prevents programs from consuming unbounded resources. The source notes that competing zkVMs like SP1 currently lack these properties, making Cairo the leading candidate under evaluation. For beginners, this matters because the choice of VM directly shapes what correctness and safety guarantees Kaspa's future smart-contract layer can provide.