diff --git a/experiments/wp24b-gc/README.md b/experiments/wp24b-gc/README.md
index 7d02867..61c03a8 100644
--- a/experiments/wp24b-gc/README.md
+++ b/experiments/wp24b-gc/README.md
@@ -1,4 +1,4 @@
-# WeirdPerformance 2.4-B — GC Safe Sweep test
+# WeirdPerformance 2.4-B1 — GC Safe Sweep ABI-fixed test
 
 Strict A/B experiment for WoW 1.12.1 build 5875.
 
@@ -9,17 +9,19 @@ Keep the validated 2.4-A binary **unchanged**:
 - `weirdperformance.dll`
 - SHA-256: `d35168ae06c19087ef9b7c68918a054640396dfbfcef0664e18e9372284b5eef`
 
-## B variant
+## B1 variant
 
 Add:
 
-- `weirdperformance_gc24b.dll`
+- `weirdperformance_gc24b1.dll`
 
 The companion changes **only Lua GC behavior**. It does not replace or rebuild the validated 2.4-A DLL.
 
+The first 2.4-B build is invalid and must not be used. It was built with an i386 Windows fastcall ABI mismatch and crashed at startup in WoW's native `lua_gc_remove_objects`. B1 is built with a pinned Zig 0.17 development toolchain and is binary-disassembly checked for the expected register ABI before distribution.
+
 The implementation is based on the historical pre-generational incremental sweep: WoW keeps its native mark, userdata/string sweep, memory shrink and finalizers. Only the main `rootgc` sweep is split into 50,000-object chunks.
 
-## Safety changes versus the old experiment
+## Safety scope
 
 - hooks only `luaC_collectgarbage` and `lua_close`;
 - no overlap with the lifecycle hooks referenced by the validated 2.4-A binary;
@@ -36,7 +38,9 @@ Keep both DLLs next to WoW and list both in `dlls.txt`:
 
 ```text
 weirdperformance.dll
-weirdperformance_gc24b.dll
+weirdperformance_gc24b1.dll
 ```
 
-Removing `weirdperformance_gc24b.dll` returns you exactly to the validated 2.4-A baseline.
+Delete the old `weirdperformance_gc24b.dll` if it is still present.
+
+Removing `weirdperformance_gc24b1.dll` returns you exactly to the validated 2.4-A baseline.