application/wasm

The type WebAssembly binaries must be served with — not a suggestion but an enforcement point, because WebAssembly.instantiateStreaming rejects any response that isn't exactly application/wasm. A misconfigured server is therefore the most common reason streaming compilation fails and code falls back to the slower ArrayBuffer path. The binary is unmistakable regardless, opening with a null byte and the letters asm.

Defined by WebAssembly Core Specification 2.0 · IANA registration. Registry facts from the IANA media-types registry via mime-db.