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Yeah, they contain binaries for Swift itself (the driver interface, the compiler, the repl, the package manager, swift-format, etc.), as well as the toolchain's dependencies (llvm, lldb, clang, the sanitizer runtimes, etc.).

There are other (also large) downloads to enable producing static binaries on Linux, and those contain the required system libraries (musl libc, libicu, libcrypto, libpthread, etc.). Those are about twice as big as they need to be, because they bundle x86 and aarch64 together.