diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index c592e81c..9c3d2c35 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -163,8 +163,9 @@ keep the score matrix in registers/L1.
 A `geist_model` is immutable, shared, read-only weights. A `geist_session` owns
 the mutable per-conversation state: KV cache, pending logits, sampler config,
 stats. Multiple sessions can share one model. The KV cache supports quantized
-modes (`INT8`, packed `INT4` — half the INT8 footprint, near-lossless with the
-optional Hadamard rotation `GEIST_KV_ROT`; and `KIVI` 2-bit) and prefix pinning
+modes (`INT8`, packed `INT4` — half the INT8 footprint, near-lossless via a
+default-on Hadamard rotation, `GEIST_KV_ROT=0` to opt out; and `KIVI` 2-bit)
+and prefix pinning
 (`geist_session_pin_prefix`) to
 amortize a constant system prompt across chat turns. Speculative decode drafts
 via an n-gram lookup over history and verifies in one batched forward.
diff --git a/include/geist.h b/include/geist.h
index b4cc16bb..89e53206 100644
--- a/include/geist.h
+++ b/include/geist.h
@@ -197,9 +197,9 @@ enum geist_kv_mode {
     GEIST_KV_KIVI = 3,
     GEIST_KV_F16  = 4,
     /* Packed symmetric 4-bit KV cache (2 values/byte, per-token per-head
-     * scale). Half the INT8 footprint, near-lossless — especially with the
-     * Hadamard rotation (GEIST_KV_ROT=1, issue #61). No per-channel/group
-     * bookkeeping (unlike KIVI). Env: GEIST_KV_INT4=1. */
+     * scale). Half the INT8 footprint, near-lossless. Enables the Hadamard
+     * rotation by default (issue #61) — GEIST_KV_ROT=0 opts out. No
+     * per-channel/group bookkeeping (unlike KIVI). Env: GEIST_KV_INT4=1. */
     GEIST_KV_INT4 = 5,
 };
 
diff --git a/src/archs/transformer/arch_state.c b/src/archs/transformer/arch_state.c
index 6629ecd0..dbfa858e 100644
--- a/src/archs/transformer/arch_state.c
+++ b/src/archs/transformer/arch_state.c
@@ -1031,10 +1031,15 @@ struct transformer_arch_session *transformer_session_alloc(struct transformer_ar
             sess->kv_kivi_enabled = false;
         }
     }
-    /* Issue #61: opt-in Hadamard rotation, only meaningful on the INT8 path. */
+    /* Issue #61: Hadamard rotation, only meaningful on the INT8 storage path.
+     * Packed INT4 rotates by DEFAULT (INT4-without-rotation is a real quality
+     * cliff and the rotation is ~free / a net win at long context); plain
+     * INT8 stays opt-in. GEIST_KV_ROT=0 opts out, =1 forces on. */
     {
-        const char *env_rot  = getenv("GEIST_KV_ROT");
-        sess->kv_rot_enabled = sess->kv_int8_enabled && env_rot != nullptr && env_rot[0] == '1';
+        const char *env_rot     = getenv("GEIST_KV_ROT");
+        const bool  rot_default = sess->kv_int4_packed_enabled;
+        const bool  rot_on      = (env_rot != nullptr) ? (env_rot[0] == '1') : rot_default;
+        sess->kv_rot_enabled    = sess->kv_int8_enabled && rot_on;
     }
     /* F16 cache: explicit request, or AUTO-resolved FP32 upgraded when the
      * backend has the fused converting append (env GEIST_KV_F16=0 forces