diff --git a/tests/rl/common_test.py b/tests/rl/common_test.py
index 77e637b9d..448405c7d 100644
--- a/tests/rl/common_test.py
+++ b/tests/rl/common_test.py
@@ -453,6 +453,30 @@ def test_pad_to_length(self):
           kwargs={},
           expected_loss=(0.1 + 0.2) / 1.0,
       ),
+      dict(
+          testcase_name="seq_mean_token_sum",
+          loss_agg_mode="seq-mean-token-sum",
+          per_token_loss_list=[[0.1, 0.2, 0.3], [0.4, 0.5, 0.6]],
+          completion_mask_list=[[1, 1, 0], [1, 1, 1]],
+          kwargs={},
+          expected_loss=0.9,
+      ),
+      dict(
+          testcase_name="seq_mean_token_sum_zero_mask",
+          loss_agg_mode="seq-mean-token-sum",
+          per_token_loss_list=[[0.1, 0.2], [0.3, 0.4]],
+          completion_mask_list=[[0, 0], [0, 0]],
+          kwargs={},
+          expected_loss=0.0,
+      ),
+      dict(
+          testcase_name="seq_mean_token_sum_partial_zero_mask",
+          loss_agg_mode="seq-mean-token-sum",
+          per_token_loss_list=[[0.1, 0.2], [0.3, 0.4]],
+          completion_mask_list=[[1, 1], [0, 0]],
+          kwargs={},
+          expected_loss=0.3,
+      ),
       dict(
           testcase_name="sequence_mean_token_sum_norm_partial_zero_mask",
           loss_agg_mode="sequence-mean-token-sum-norm",
diff --git a/tunix/rl/agentic/agentic_grpo_learner.py b/tunix/rl/agentic/agentic_grpo_learner.py
index 1e635d9b9..654f6b4b3 100644
--- a/tunix/rl/agentic/agentic_grpo_learner.py
+++ b/tunix/rl/agentic/agentic_grpo_learner.py
@@ -69,7 +69,7 @@ class GRPOConfig(agentic_rl_learner.AgenticRLConfig):
     policy_loss_fn: Name of the policy loss function.
     loss_agg_mode: Method for aggregating the loss. Supported values:
       "token-mean", "sequence-mean-token-mean", "sequence-mean-token-scale",
-      "sequence-mean-token-sum-norm".
+      "seq-mean-token-sum", "sequence-mean-token-sum-norm".
     num_generations: Number of samples per prompt (G in the paper). Must be > 1.
     num_iterations: Number of GRPO iterations per batch (μ in the paper).
     beta: KL penalty coefficient.
@@ -624,7 +624,6 @@ def grpo_loss_fn(
   per_token_logps = jnp.astype(per_token_logps, jnp.float32)
   # TODO(tsbao): We should handle token level advantages.
   advantages = jnp.astype(train_example.advantages, jnp.float32)
-
   if train_example.old_per_token_logps is None:
     old_per_token_logps = jax.lax.stop_gradient(per_token_logps)
   else:
diff --git a/tunix/rl/common.py b/tunix/rl/common.py
index 09d24650d..a8d507848 100644
--- a/tunix/rl/common.py
+++ b/tunix/rl/common.py
@@ -526,6 +526,12 @@ def aggregate_loss(
         norm, min=1e-6
     )
     loss = seq_loss.sum() / non_zero_rows
+  elif loss_agg_mode == "seq-mean-token-sum":
+    # 1) sum token losses within each sequence
+    # 2) average only across sequences that have at least one valid token
+    seq_loss = (per_token_loss * completion_mask).sum(axis=-1)
+    seq_mask = (completion_mask.sum(axis=-1) > 0).astype(jnp.float32)
+    loss = (seq_loss * seq_mask).sum() / jnp.clip(seq_mask.sum(), min=1e-6)
   elif loss_agg_mode == "sequence-mean-token-sum-norm":
     # Get custom normalization factor from kwargs, default to number of
     # non-empty rows.
@@ -538,7 +544,8 @@ def aggregate_loss(
     raise ValueError(
         f"Unsupported loss aggregation mode: {loss_agg_mode}. Supported modes:"
         " 'token-mean', 'sequence-mean-token-mean',"
-        " 'sequence-mean-token-scale', 'sequence-mean-token-sum-norm'."
+        " 'sequence-mean-token-scale', 'seq-mean-token-sum',"
+        " 'sequence-mean-token-sum-norm'."
     )
   return loss
 
diff --git a/tunix/rl/grpo/grpo_learner.py b/tunix/rl/grpo/grpo_learner.py
index 5d6b64d0a..fd30a5660 100644
--- a/tunix/rl/grpo/grpo_learner.py
+++ b/tunix/rl/grpo/grpo_learner.py
@@ -50,8 +50,10 @@ class GRPOConfig(algo_config_lib.AlgorithmConfig):
     algo_variant: The algorithm variant to use. Default: `grpo`.
     advantage_estimator: The advantage estimator to use. Default: `grpo`.
     policy_loss_fn: The policy loss function to use. Default: `grpo`.
-    loss_agg_mode: The aggregation mode for the loss function. Default:
-      `sequence-mean-token-mean`.
+    loss_agg_mode: The aggregation mode for the loss function. Supported values
+      include `token-mean`, `sequence-mean-token-mean`,
+      `sequence-mean-token-scale`, `seq-mean-token-sum`, and
+      `sequence-mean-token-sum-norm`. Default: `sequence-mean-token-mean`.
     reward_manager: The reward manager to use. Default: `sequence-level`.
     loss_algo: The loss algorithm to use. To be deprecated.
     num_generations: The number of times the policy generates multiple responses