diff --git a/atroposlib/envs/base.py b/atroposlib/envs/base.py
index 6180af09..278a5a05 100644
--- a/atroposlib/envs/base.py
+++ b/atroposlib/envs/base.py
@@ -178,7 +178,6 @@ class BaseEnvConfig(BaseModel):
 
 
 class BaseEnv(ABC):
-
     name: Optional[str] = None
     env_config_cls: BaseEnvConfig = BaseEnvConfig
     server_cls: APIServer = APIServer
@@ -224,7 +223,6 @@ class BaseEnv(ABC):
         self.checkpoint_dir = ""
         self.checkpoint_interval = -1
         if self.config.data_path_to_save_groups is not None:
-
             Path(self.config.data_path_to_save_groups).parent.mkdir(
                 parents=True, exist_ok=True
             )
@@ -286,7 +284,9 @@ class BaseEnv(ABC):
             "Handle env single method must be implemented in subclass "
         )
 
-    async def collect_trajectories(self, item: Item) -> Tuple[
+    async def collect_trajectories(
+        self, item: Item
+    ) -> Tuple[
         Union[
             Optional[ScoredDataGroup], List[Optional[ScoredDataGroup]], List[Any | None]
         ],
@@ -830,7 +830,7 @@ class BaseEnv(ABC):
             group.setdefault("group_overrides", None)
 
             for mask in group["masks"]:
-                self.completion_lengths.append(len(mask))
+                self.completion_lengths.append(sum(m != -100 for m in mask))
 
             if self.max_token_len <= 0:
                 warnings.warn(
@@ -1461,9 +1461,10 @@ class BaseEnv(ABC):
         """
 
         # Get the default configurations from the specific environment class via config_init
-        default_env_config_from_init, default_server_configs_from_init = (
-            cls.config_init()
-        )
+        (
+            default_env_config_from_init,
+            default_server_configs_from_init,
+        ) = cls.config_init()
 
         # Define namespace prefixes
         env_full_prefix = f"{ENV_NAMESPACE}{NAMESPACE_SEP}"
@@ -1549,9 +1550,9 @@ class BaseEnv(ABC):
                 env_config_dict_base["ensure_scores_are_not_same"] = False
                 env_config_dict_base["include_messages"] = True
                 if env_config_dict_base.get("data_path_to_save_groups") is None:
-                    env_config_dict_base["data_path_to_save_groups"] = (
-                        f"data/{cls.name or 'groups'}.jsonl"
-                    )
+                    env_config_dict_base[
+                        "data_path_to_save_groups"
+                    ] = f"data/{cls.name or 'groups'}.jsonl"
                 env_config_dict_base["use_wandb"] = True
 
                 env_config_dict = merge_dicts(
@@ -1729,9 +1730,10 @@ class BaseEnv(ABC):
             type: The CliEvaluateConfig class for evaluate commands.
         """
         # Get the default configurations from the specific environment class via config_init
-        default_env_config_from_init, default_server_configs_from_init = (
-            cls.config_init()
-        )
+        (
+            default_env_config_from_init,
+            default_server_configs_from_init,
+        ) = cls.config_init()
 
         # Define namespace prefixes
         env_full_prefix = f"{ENV_NAMESPACE}{NAMESPACE_SEP}"