diff --git a/vizier/_src/algorithms/designers/gp/acquisitions.py b/vizier/_src/algorithms/designers/gp/acquisitions.py
index 96fab621d..f184c0a98 100644
--- a/vizier/_src/algorithms/designers/gp/acquisitions.py
+++ b/vizier/_src/algorithms/designers/gp/acquisitions.py
@@ -170,6 +170,50 @@ def score_with_aux(
 # Vizier library acquisition functions use `flax.struct`, instead of `attrs` and
 # a hash function, so that acquisition functions can be passed as args to JIT-ed
 # functions without triggering retracing when attribute values change.
+@struct.dataclass
+class MEANPENALIZED(AcquisitionFunction):
+  """Mean with relative region AcquisitionFunction."""
+
+  coefficient: float = 1.8
+  max_lcb_thresh: float = -jnp.inf
+
+  def __call__(
+      self,
+      dist: tfd.Distribution,
+      seed: Optional[jax.random.KeyArray] = None,
+  ) -> jax.Array:
+    del seed
+    ucb = dist.mean() + self.coefficient * dist.stddev()
+    acquisition = jnp.where(
+        (ucb >= self.max_lcb_thresh),
+        dist.mean(),
+        -1e12 - ucb,
+    )
+    return acquisition
+
+
+@struct.dataclass
+class STDPENALIZED(AcquisitionFunction):
+  """Standard Deviation with relative region AcquisitionFunction."""
+
+  coefficient: float = 1.8
+  max_lcb_thresh: float = -jnp.inf
+
+  def __call__(
+      self,
+      dist: tfd.Distribution,
+      seed: Optional[jax.random.KeyArray] = None,
+  ) -> jax.Array:
+    del seed
+    ucb = dist.mean() + self.coefficient * dist.stddev()
+    acquisition = jnp.where(
+        (ucb >= self.max_lcb_thresh),
+        dist.stddev(),
+        -1e12 - ucb,
+    )
+    return acquisition
+
+
 @struct.dataclass
 class UCB(AcquisitionFunction):
   """UCB AcquisitionFunction."""