diff --git a/core/front/tiny_front_c23.h b/core/front/tiny_front_c23.h
index 30599b61..dd390b33 100644
--- a/core/front/tiny_front_c23.h
+++ b/core/front/tiny_front_c23.h
@@ -46,17 +46,19 @@ static inline int tiny_front_c23_enabled(void) {
     return cached;
 }
 
-// Refill target (conservative start: 16 blocks)
-// Tunable via A/B testing: 16/32/64
-// Smaller = lower latency, higher refill frequency
-// Larger = higher latency, lower refill frequency
+// Refill target: 64 blocks (optimized via A/B testing)
+// A/B Results (100K iterations):
+//   128B: refill=64 → 9.55M ops/s (+15.5% vs baseline 8.27M)
+//   256B: refill=64 → 8.47M ops/s (+7.2% vs baseline 7.90M)
+//   256B: refill=32 → 8.61M ops/s (+9.0%, slightly better for 256B)
+// Decision: refill=64 for balanced performance across C2/C3
 static inline int tiny_front_c23_refill_target(int class_idx) {
     (void)class_idx;
     static __thread int target = -1;
     if (__builtin_expect(target == -1, 0)) {
         const char* env = getenv("HAKMEM_TINY_FRONT_C23_REFILL");
-        target = (env && *env) ? atoi(env) : 16;
-        if (target <= 0) target = 16;
+        target = (env && *env) ? atoi(env) : 64;  // Default: 64 (A/B optimized)
+        if (target <= 0) target = 64;
         if (target > 128) target = 128;  // Cap at 128 to avoid excessive latency
     }
     return target;