WebAssembly (Wasm) has emerged as a portable compilation target enabling near-native performance in web browsers and server environments. This paper benchmarks WebAssembly runtime performance focusing on WASI (WebAssembly System Interface), the Component Model, and cross-language interface types for serverless computing. We evaluate leading Wasm runtimes including Wasmtime, WasmEdge, and WAMR across startup latency, execution throughput, and memory consumption metrics. Cold start latency measurements reveal that Wasm runtimes achieve 1-10ms initialization compared to 100-1000ms for traditional containers, making Wasm ideal for serverless functions. The Component Model enables composable Wasm modules with type-safe interfaces, reducing inter-module call overhead by 10×. WASI provides standardized system APIs achieving 80-95% of native Linux performance for I/O operations. Benchmarks across CPU-intensive, memory-bound, and I/O-heavy workloads demonstrate that optimized Wasm code reaches 70-95% of native C/C++ performance. We analyze trade-offs between security isolation, performance overhead, and portability. Implementation strategies for serverless platforms including function composition, resource limits, and polyglot execution are discussed. Our findings indicate WebAssembly offers a compelling foundation for next-generation serverless computing with superior cold start performance and cross-platform portability.