diff --git a/engine/MUNGA/JMOVER.cpp b/engine/MUNGA/JMOVER.cpp
index 5fad336..bc35236 100644
--- a/engine/MUNGA/JMOVER.cpp
+++ b/engine/MUNGA/JMOVER.cpp
@@ -135,7 +135,10 @@ void
 	)
 {
 	Check(this);
-	static const int sPerf = getenv("BT_PERF_LOG") ? 1 : 0;
+	// DEFAULT ON (operator, 2026-08-09): every player's session log should
+	// carry this -- cross-machine comparison is the point.  BT_PERF_LOG=0
+	// opts out.  Cost: ~2 QPC reads per call, microseconds per second.
+	static const int sPerf = !(getenv("BT_PERF_LOG") && *getenv("BT_PERF_LOG") == '0');
 	LARGE_INTEGER t0, t1, fq;
 	++gBTSegWCalls;
 	if (sPerf) QueryPerformanceCounter(&t0);
diff --git a/engine/MUNGA_L4/L4VIDEO.cpp b/engine/MUNGA_L4/L4VIDEO.cpp
index a8d118a..cfc7570 100644
--- a/engine/MUNGA_L4/L4VIDEO.cpp
+++ b/engine/MUNGA_L4/L4VIDEO.cpp
@@ -9039,7 +9039,7 @@ void DPLRenderer::ExecuteImplementation(RendererComplexity, RendererOrigin::Inte
 			// invalidation passes (the expensive arm the #141 sweep may have
 			// multiplied); ms = time inside the accessor for the whole window.
 			{
-				static const int sSegPerf = getenv("BT_PERF_LOG") ? 1 : 0;
+				static const int sSegPerf = !(getenv("BT_PERF_LOG") && *getenv("BT_PERF_LOG") == '0');
 				extern int gBTSegWCalls, gBTSegWDirty;
 				extern double gBTSegWMs;
 				if (sSegPerf)