The article evaluates thirteen modern languages that claim to be successors to C, the foundational substrate of operating systems, runtimes, and libraries. By applying five stringent filters—freestanding compilation, deterministic layout, stable C interoperability, absence of a mandatory runtime, and toolchain visibility—the analysis isolates the languages that can truly occupy C’s position in the software stack. Only five languages—Rust, Zig, Odin, Hare, and C3—pass all filters in their default or primary modes, demonstrating that they can be used for kernel, firmware, and low‑level system development without relying on a garbage collector or runtime.

The remaining languages either fail the filters outright or require restrictive modes that strip away their distinguishing features. This distinction is critical for developers and organizations deciding which language to adopt for future systems infrastructure, as it directly impacts safety guarantees, performance, and ecosystem maturity. The findings highlight a shift toward safer, more explicit memory models while preserving the familiar C syntax, signaling a gradual diversification of the substrate layer in modern computing.