diff --git a/e2e/browser-v3/arena/bu_real.py b/e2e/browser-v3/arena/bu_real.py
index 1673f487..62579828 100644
--- a/e2e/browser-v3/arena/bu_real.py
+++ b/e2e/browser-v3/arena/bu_real.py
@@ -20,7 +20,6 @@ from pathlib import Path
 
 sys.path.insert(0, str(Path(__file__).resolve().parent))
 
-import browsergym.assistantbench  # noqa: F401  registers the live-web research envs
 import browsergym.miniwob  # noqa: F401  registers the 125 envs
 import gymnasium as gym
 
@@ -96,6 +95,8 @@ def reap_leftover_browsers() -> None:
 
 def make_env(task: str, seed: int, max_steps: int):
     patch_launch_with_cdp_port()
+    if "." in task:
+        import browsergym.assistantbench  # noqa: F401  lazy: HF datasets machinery breaks playwright
     env_id = f"browsergym/{task}" if "." in task else f"browsergym/miniwob.{task}"
     env = gym.make(env_id, headless=True, max_episode_steps=max_steps)
     obs, _ = env.reset(seed=seed)
diff --git a/e2e/browser-v3/arena/run.py b/e2e/browser-v3/arena/run.py
index 3acef197..df113efa 100644
--- a/e2e/browser-v3/arena/run.py
+++ b/e2e/browser-v3/arena/run.py
@@ -19,7 +19,6 @@ from typing import Any
 
 sys.path.insert(0, str(Path(__file__).resolve().parent))
 
-import browsergym.assistantbench  # noqa: F401  registers the 215 live-web research envs
 import browsergym.miniwob  # noqa: F401  importing is what registers the 125 envs
 import gymnasium as gym
 
@@ -93,6 +92,11 @@ def run_episode(arm: str, task: str, seed: int, rec: Recorder, args: argparse.Na
                                       strict=False, multiaction=True)
             # A task name containing '.' is a full BrowserGym suffix (assistantbench.validation.3);
             # bare names stay MiniWoB. One grader per suite, none of them ours.
+            if "." in task:
+                # Lazy: importing assistantbench pulls HF datasets' multiprocessing machinery in,
+                # which corrupts sync-playwright's event loop for the WHOLE process -- 248 of 252
+                # v16 MiniWoB episodes died to it before this moved out of module scope.
+                import browsergym.assistantbench  # noqa: F401
             env_id = f"browsergym/{task}" if "." in task else f"browsergym/miniwob.{task}"
             holder.append(gym.make(env_id, headless=not args.headed,
                                    max_episode_steps=args.max_steps, wait_for_user_message=False,