diff --git a/verifiers/envs/environment.py b/verifiers/envs/environment.py
index 3959759d5..355305c81 100644
--- a/verifiers/envs/environment.py
+++ b/verifiers/envs/environment.py
@@ -36,6 +36,7 @@
     Messages,
     MessageType,
     ModelResponse,
+    OnGroupComplete,
     RolloutInput,
     RolloutTiming,
     SamplingArgs,
@@ -663,6 +664,7 @@ async def generate(
         save_results: bool = False,
         save_every: int = -1,
         use_tqdm: bool = True,
+        on_group_complete: OnGroupComplete | None = None,
     ) -> GenerateOutputs:
         """
         Generate rollouts for a set of inputs by group.
@@ -725,6 +727,7 @@ async def generate(
             )
 
         groups_completed = 0
+        total_groups = len(group_list)
         all_states: list[State] = []
         try:
             for coro in asyncio.as_completed(group_tasks.keys()):
@@ -735,7 +738,11 @@ async def generate(
                 if pbar is not None:
                     pbar.update(1)
 
-                # save intermediate results
+                if on_group_complete is not None:
+                    await on_group_complete(
+                        group_states, groups_completed, total_groups
+                    )
+
                 if (
                     save_results
                     and save_every > 0
@@ -842,6 +849,7 @@ async def evaluate(
         state_columns: list[str] | None = None,
         save_results: bool = False,
         save_every: int = -1,
+        on_group_complete: OnGroupComplete | None = None,
         **kwargs,
     ) -> GenerateOutputs:
         """
@@ -860,6 +868,7 @@ async def evaluate(
             state_columns=state_columns,
             save_results=save_results,
             save_every=save_every,
+            on_group_complete=on_group_complete,
             **kwargs,
         )
 
diff --git a/verifiers/types.py b/verifiers/types.py
index ab75bb91e..deac2c67d 100644
--- a/verifiers/types.py
+++ b/verifiers/types.py
@@ -49,6 +49,8 @@
 GroupRewardFunc = Callable[..., list[float] | Awaitable[list[float]]]
 RewardFunc = IndividualRewardFunc | GroupRewardFunc
 
+OnGroupComplete = Callable[["list[State]", int, int], Awaitable[None]]
+
 
 class TrajectoryStepTokens(TypedDict):
     prompt_ids: list[int]
diff --git a/verifiers/utils/eval_utils.py b/verifiers/utils/eval_utils.py
index d8e1a9dc3..9dc100a4d 100644
--- a/verifiers/utils/eval_utils.py
+++ b/verifiers/utils/eval_utils.py
@@ -11,7 +11,13 @@
 from datasets.utils import logging as ds_logging
 
 import verifiers as vf
-from verifiers.types import Endpoints, EvalConfig, GenerateMetadata, GenerateOutputs
+from verifiers.types import (
+    Endpoints,
+    EvalConfig,
+    GenerateMetadata,
+    GenerateOutputs,
+    OnGroupComplete,
+)
 from verifiers.utils.client_utils import setup_client
 from verifiers.utils.logging_utils import print_prompt_completions_sample
 from verifiers.utils.message_utils import messages_to_printable, sanitize_tool_calls
@@ -98,8 +104,10 @@ def print_results(results: GenerateOutputs, num_samples: int = 1):
             print(out)
 
 
-async def run_evaluation(config: EvalConfig) -> GenerateOutputs:
-    # set up AsyncOpenAI client with high limits to prevent timeouts
+async def run_evaluation(
+    config: EvalConfig,
+    on_group_complete: OnGroupComplete | None = None,
+) -> GenerateOutputs:
     client = setup_client(
         config.client_config,
     )
@@ -107,10 +115,8 @@ async def run_evaluation(config: EvalConfig) -> GenerateOutputs:
         f"Initialized AsyncOpenAI client with base_url: {config.client_config.api_base_url}"
     )
 
-    # load environment
     vf_env = vf.load_environment(env_id=config.env_id, **config.env_args)
 
-    # run evaluation
     results_path = get_eval_results_path(config)
     logger.info(f"Starting evaluation with model: {config.model}")
     logger.info(
@@ -130,6 +136,7 @@ async def run_evaluation(config: EvalConfig) -> GenerateOutputs:
         state_columns=config.state_columns,
         save_results=config.save_results,
         save_every=config.save_every,
+        on_group_complete=on_group_complete,
     )
     end_time = time.time()
     logger.info(f"Evaluation completed in {end_time - start_time:.2f} seconds")