diff --git a/mcpp.toml b/mcpp.toml
index 8cc3558..7ca1959 100644
--- a/mcpp.toml
+++ b/mcpp.toml
@@ -10,6 +10,7 @@
 members = [
     "tests/examples/archive",
     "tests/examples/asio",
+    "tests/examples/asm-macos-spike",
     "tests/examples/asio-module",
     "tests/examples/build-mcpp",
     "tests/examples/cjson",
diff --git a/tests/examples/asm-macos-spike/asm/add_arm64.S b/tests/examples/asm-macos-spike/asm/add_arm64.S
new file mode 100644
index 0000000..301784c
--- /dev/null
+++ b/tests/examples/asm-macos-spike/asm/add_arm64.S
@@ -0,0 +1,9 @@
+// R2 spike: minimal aarch64 GAS .S — proves mcpp assembles + links a GAS .S TU
+// on macos-15 (the #1 macOS unknown; FFmpeg/OpenCV SIMD on arm64 is GAS .S).
+// macOS arm64 ABI: w0=arg0, w1=arg1, result in w0; C symbol `asm_add` -> `_asm_add`.
+.text
+.p2align 2
+.globl _asm_add
+_asm_add:
+    add w0, w0, w1
+    ret
diff --git a/tests/examples/asm-macos-spike/mcpp.toml b/tests/examples/asm-macos-spike/mcpp.toml
new file mode 100644
index 0000000..4724bb8
--- /dev/null
+++ b/tests/examples/asm-macos-spike/mcpp.toml
@@ -0,0 +1,9 @@
+# R2 spike (TEMP — remove after the macOS .S path is proven): compile one
+# aarch64 GAS .S unit on macos-15 and link it into a test. cfg(macos)-gated so
+# the aarch64 asm is only assembled on macOS; a no-op main elsewhere.
+[package]
+name    = "asm-macos-spike-tests"
+version = "0.1.0"
+
+[target.'cfg(macos)'.build]
+sources = ["asm/add_arm64.S"]
diff --git a/tests/examples/asm-macos-spike/tests/spike.cpp b/tests/examples/asm-macos-spike/tests/spike.cpp
new file mode 100644
index 0000000..27bc58f
--- /dev/null
+++ b/tests/examples/asm-macos-spike/tests/spike.cpp
@@ -0,0 +1,11 @@
+#ifdef __APPLE__
+import std;
+extern "C" int asm_add(int, int);   // defined in asm/add_arm64.S
+int main() {
+    int r = asm_add(2, 3);
+    std::println("asm-macos-spike: aarch64 .S linked OK, asm_add(2,3)={}", r);
+    return r == 5 ? 0 : 1;
+}
+#else
+int main() { return 0; }
+#endif