diff --git a/config/backpack.yaml b/config/backpack.yaml
index 735d40c01..0fe93b539 100644
--- a/config/backpack.yaml
+++ b/config/backpack.yaml
@@ -12,7 +12,7 @@ model:
 trainer:
   tracker:
     project: "levanter"
-    tags: [ "openwebtext", "backpack" ]
+    tags: ["openwebtext", "backpack"]
 
   mp: p=f32,c=bfloat16
 
@@ -21,5 +21,5 @@ trainer:
   model_axis_size: 1
 
 optimizer:
-  learning_rate: 6E-4
+  learning_rate: 6e-4
   weight_decay: 0.1
diff --git a/src/levanter/callbacks.py b/src/levanter/callbacks.py
index 135d10dd5..9ff544bd8 100644
--- a/src/levanter/callbacks.py
+++ b/src/levanter/callbacks.py
@@ -17,6 +17,7 @@
 from tqdm_loggable import tqdm_logging
 from tqdm_loggable.auto import tqdm
 
+import haliax as hax
 import haliax.nn
 from haliax import NamedArray, is_named_array
 from haliax.jax_utils import is_jax_array_like
@@ -30,6 +31,8 @@
 from levanter.utils import flop_utils, jax_utils
 from levanter.utils.jax_utils import barrier_sync, jnp_to_python
 from levanter.utils.logging import save_xla_dumps_to_wandb
+from levanter.utils.stat_utils import RunningMean
+from levanter.utils.types import Extras
 from levanter.visualization import compute_and_visualize_log_probs as viz_probs
 
 
@@ -145,10 +148,8 @@ async def compute_length():
 
 
 def eval_loss_loop(loss_fn, model, dataset, max_batches: Optional[int] = None, name: Optional[str] = None):
-    total_loss = 0.0
-    total_load_time = 0.0
-    total_loss_time = 0.0
-    n = 0
+    loss = RunningMean(jnp.zeros(()), jnp.zeros(()))
+    extras: Extras = {}
 
     if name is not None:
         desc = f"eval {name}"
@@ -159,28 +160,27 @@ def eval_loss_loop(loss_fn, model, dataset, max_batches: Optional[int] = None, n
     pbar = tqdm(dataset, desc=desc, position=1, leave=False, total=max_batches)
 
     iter_ = iter(pbar)
+    n = 0
     while True:
-        time_in = time.time()
+        n += 1
         batch = next(iter_, None)
         if batch is None:
             break
-        load_time = time.time() - time_in
-        total_load_time += load_time
-        loss = loss_fn(model, batch)
-        total_loss += loss.item()
-        n += 1
-        loss_time = time.time() - time_in - load_time
-        total_loss_time += loss_time
+        losses, where, extras = loss_fn(model, batch)
+        mean_loss = hax.mean(losses, where=where)
+        loss += RunningMean(mean_loss, where.sum())
+        for k, v in extras.items():
+            if k not in extras:
+                extras[k] = v
+            else:
+                extras[k] += v
 
-        pbar.set_postfix(loss=total_loss / n)
+        pbar.set_postfix(loss=loss.mean.item())
 
         if max_batches is not None and n >= max_batches:
             break
 
-    if n > 0:
-        total_loss /= n
-
-    return total_loss
+    return loss.item(), {k: v.item() for k, v in extras.items()}
 
 
 def compute_validation_loss(
@@ -190,12 +190,14 @@ def compute_validation_loss(
     name: Optional[str] = None,
 ):
     def compute_loss(info: StepInfo):
-        loss = eval_loss_loop(loss_fn, info.model, dataset, max_batches=max_batches, name=name)
+        loss, extras = eval_loss_loop(loss_fn, info.model, dataset, max_batches=max_batches, name=name)
 
         prefix = "eval"
         if name:
             prefix += "/" + name
-        levanter.tracker.log({f"{prefix}/loss": loss}, step=info.step)
+        levanter.tracker.log(
+            {f"{prefix}/loss": loss} | {f"{prefix}/{k}": v for k, v in extras.items()}, step=info.step
+        )
 
         if name:
             logger.info(f"{name} validation loss: {loss:.3f}")
diff --git a/src/levanter/doremi.py b/src/levanter/doremi.py
index cdcfe68cd..6cd14d496 100644
--- a/src/levanter/doremi.py
+++ b/src/levanter/doremi.py
@@ -134,12 +134,17 @@ def doremi_step(state: DoremiState, ref, batch, domains):
         proxy = inference_mode(state.model, False)
         with hax.axis_mapping(trainer.compute_axis_mapping):
             # calculate per-token losses for proxy and ref
-            proxy_losses, proxy_loss_bwd = eqx.filter_vjp(lambda p: loss_fn(p, batch, reduction_axis=()), proxy)
-            ref_losses = loss_fn(ref, batch, reduction_axis=())
+            def scalar_loss_fn(p, batch):
+                ret, _, _ = loss_fn(p, batch)
+                return ret
+
+            proxy_losses, proxy_loss_bwd = eqx.filter_vjp(lambda p: scalar_loss_fn(p, batch), proxy)
+            ref_losses = scalar_loss_fn(ref, batch)
 
             # calculate excess losses, aggregate per-domain losses
             excess_losses = proxy_losses - ref_losses
             clipped_losses = hax.maximum(excess_losses, 0)
+            print(clipped_losses.shape)
             per_domain_losses = _compute_per_domain_losses(clipped_losses, Domain, domains)
 
             # Update domain weights
diff --git a/src/levanter/grad_accum.py b/src/levanter/grad_accum.py
index 8dbdc2c30..3b77a75bd 100644
--- a/src/levanter/grad_accum.py
+++ b/src/levanter/grad_accum.py
@@ -1,11 +1,9 @@
-import enum
 import functools
 from typing import Callable, Optional, ParamSpec, TypeVar
 
 import equinox as eqx
 import jax
 import jax.numpy as jnp
-import jax.tree as jtu
 from jax.lax import with_sharding_constraint
 from jax.sharding import PartitionSpec
 
@@ -25,34 +23,6 @@
 X = TypeVar("X", contravariant=True)  # Input
 
 
-class ReductionType(enum.Enum):
-    SUM = enum.auto()
-    MEAN = enum.auto()
-    # TODO: add MAX?
-
-
-def apply_updates_running(acc, r, updates, overwrites):
-    def _running_sum_updates(u, p):
-        if u is None:
-            return p
-        else:
-            return p * (1 - r) + u * r
-
-    def _is_none(x):
-        return x is None
-
-    def _apply_update(tree, update, overwrite):
-        if overwrite is not None:
-            return overwrite
-
-        return jtu.map(_running_sum_updates, update, tree, is_leaf=_is_none)
-
-    def is_leaf(x):
-        return x is None or isinstance(x, hq.OverwriteWithGradient)
-
-    return jtu.map(_apply_update, acc, updates, overwrites, is_leaf=is_leaf)
-
-
 # TODO: should we use a custom_jvp on microbatched?
 
 # cf https://github.com/google-research/t5x/blob/main/t5x/trainer.py#L617
@@ -108,6 +78,8 @@ def microbatched(
         @functools.wraps(loss_fn)
         def no_accum_loss_fn(*args, **kwargs):
             losses, where, extras = loss_fn(*args, **kwargs)
+            seen_tokens = where.sum().scalar()
+            extras["seen_tokens"] = seen_tokens
             return hax.mean(losses, where=where).scalar(), extras
 
         return eqx.filter_value_and_grad(no_accum_loss_fn, has_aux=True)
@@ -119,7 +91,7 @@ def no_accum_loss_fn(*args, **kwargs):
     @functools.wraps(loss_fn)
     def accum_loss_fn(*args, **kwargs):
         losses, where, extras = loss_fn(*args, **kwargs)
-        return hax.mean(losses, where=where).scalar(), (where.sum(), extras)
+        return hax.sum(losses, where=where).scalar(), (where.sum(), extras)
 
     grad_fn = eqx.filter_value_and_grad(accum_loss_fn, has_aux=True)
 
@@ -154,17 +126,20 @@ def loop(acc, microbatch_and_key):
 
                 # TODO: this uses the latest value for the scale for fp8, which seems not ideal but probably ok?
                 overwrites, updates = hq.partition_for_grad_overwrite(grads_mb)
-                r = n_mb / (total + n_mb)
-                loss = loss + (loss_mb - loss) * r
-                grads = apply_updates_running(grads, r, updates, overwrites)
+                grads = hq.apply_updates(grads, updates, overwrites)
                 grads = hax.shard_with_axis_mapping(grads, accum_axis_mapping)
-            print(loss, loss_mb, r)
+                loss += loss_mb
+                total += n_mb
+
             return (loss, (total, {k: v + extras_mb[k] for k, v in extras.items()})), grads
 
         with jax.named_scope("microbatched"):
-            (loss, (_, extras)), grads, = hax.fold(
+            (loss, (total, extras)), grads, = hax.fold(
                 loop, AccumStep
             )(acc, (args, kwargs, key))
+            grads = jax.tree_util.tree_map(lambda x: x / total, grads)
+            loss /= total
+            extras["seen_tokens"] = total
 
         return (loss, extras), grads
 
diff --git a/src/levanter/trainer.py b/src/levanter/trainer.py
index 2a454362c..cbb272dcd 100644
--- a/src/levanter/trainer.py
+++ b/src/levanter/trainer.py
@@ -43,7 +43,7 @@
 from levanter.utils import cloud_utils, fsspec_utils
 from levanter.utils.jax_utils import create_fsdp_mesh, zeros_like_tree
 from levanter.utils.tree_utils import inference_mode
-from levanter.utils.types import ComputeLossFunction, FilterSpec
+from levanter.utils.types import ComputeLossFunction, Extras, FilterSpec
 
 
 logger = pylogging.getLogger(__name__)
@@ -391,10 +391,10 @@ def train_step(self, state: S, batch: X, **batch_kwargs) -> StepInfo[S]:
 
         with capture_time() as step_time:
             if hooks_this_time:
-                loss, new_state, cb_states = self._jit_train_step_fn(state, batch, batch_kwargs)
+                loss, new_state, extras, cb_states = self._jit_train_step_fn(state, batch, batch_kwargs)
                 # force the loss so timing numbers are accurate. laziness isn't going to help here (i think?)
             else:
-                loss, new_state = self._jit_train_step_fn_no_hook(state, batch, batch_kwargs)
+                loss, new_state, extras = self._jit_train_step_fn_no_hook(state, batch, batch_kwargs)
             loss = loss.item()  # type: ignore
 
             info = StepInfo(new_state, loss, step_time())
@@ -404,7 +404,8 @@ def train_step(self, state: S, batch: X, **batch_kwargs) -> StepInfo[S]:
                 if hooks_this_time:
                     self.hooks.run_jit_hooks_outside_step(info, cb_states)
 
-            levanter.tracker.log({"throughput/hook_time": hook_time()}, step=info.step)
+            log_items = {k: v.item() for k, v in extras.items()} | {"throughput/hook_time": hook_time()}
+            levanter.tracker.log(log_items, step=info.step)
 
         return info
 
@@ -525,11 +526,13 @@ def _jit_train_step_fn_no_hook(self):
 
     def _train_step(
         self, state: S, batch, batch_kwargs, _no_hooks=False
-    ) -> tuple[Scalar, S, Sequence[CBInfo]] | tuple[Scalar, S]:
+    ) -> tuple[Scalar, S, Extras, Sequence[CBInfo]] | tuple[Scalar, S, Extras]:
         key, new_key = jax.random.split(state.training_key)
         model = inference_mode(state.model, False)
 
-        loss, grads = self._compute_gradients_microbatched(self.loss_fn, model, batch, **batch_kwargs, key=key)
+        (loss, extras), grads = self._compute_gradients_microbatched(
+            self.loss_fn, model, batch, **batch_kwargs, key=key
+        )
 
         with hax.axis_mapping(self.parameter_axis_mapping):
             if not _no_hooks:
@@ -545,11 +548,13 @@ def obj_fun(trainable_model):
         new_state = state.take_step(grads, obj_fun=obj_fun)
         new_state = hax.shard(new_state, self.parameter_axis_mapping)
         if _no_hooks:
-            return loss, new_state
+            return loss, new_state, extras
         else:
-            return loss, new_state, hook_infos
+            return loss, new_state, extras, hook_infos
 
-    def _compute_gradients_microbatched(self, loss_fn, model: M, batch: X, **batch_kwargs) -> tuple[Scalar, M]:
+    def _compute_gradients_microbatched(
+        self, loss_fn, model: M, batch: X, **batch_kwargs
+    ) -> tuple[tuple[Scalar, Extras], M]:
         mbs = self.config.microbatch_size
         grad_fn = microbatched(
             loss_fn,
diff --git a/src/levanter/utils/stat_utils.py b/src/levanter/utils/stat_utils.py
index 6111be42e..895003cf4 100644
--- a/src/levanter/utils/stat_utils.py
+++ b/src/levanter/utils/stat_utils.py
@@ -1,13 +1,26 @@
-import typing
+from typing import TypeAlias
 
 import equinox as eqx
 import jax.numpy as jnp
 import numpy as np
+from typing_extensions import Self
 
 import haliax as hax
 
+from levanter.utils.types import Accumulatable
 
-Arrayish: typing.TypeAlias = hax.NamedArray | np.ndarray | jnp.ndarray
+
+Arrayish: TypeAlias = hax.NamedArray | np.ndarray | jnp.ndarray
+
+
+class SumScalar(Accumulatable):
+    value: jnp.ndarray
+
+    def item(self) -> float:
+        return self.value.item()
+
+    def __add__(self, other: Self) -> Self:
+        return SumScalar(self.value + other.value)
 
 
 class RunningMean(eqx.Module):
@@ -27,6 +40,9 @@ def add(self, x: Arrayish, total: Arrayish) -> "RunningMean":
         new_total = self.total + total
         return RunningMean(new_mean, new_total)
 
+    def item(self) -> float:
+        return self.mean.item()
+
     def __add__(self, other: "RunningMean"):
         return self.add(other.mean, other.total)
 
diff --git a/src/levanter/utils/types.py b/src/levanter/utils/types.py
index 900b23985..dafc0791d 100644
--- a/src/levanter/utils/types.py
+++ b/src/levanter/utils/types.py
@@ -1,6 +1,10 @@
-from typing import Any, Callable, Protocol, Tuple, TypeVar, Union
+import abc
+from typing import Any, Callable, Dict, Protocol, Tuple, TypeAlias, TypeVar, Union
 
+import equinox as eqx
+import jax
 from jaxtyping import PyTree
+from typing_extensions import Self
 
 import haliax as hax
 from haliax.types import Scalar
@@ -10,6 +14,19 @@
 M_con = TypeVar("M_con", contravariant=True)  # Model
 X = TypeVar("X", contravariant=True)  # Input
 
+
+class Accumulatable(abc.ABC, eqx.Module):
+    @abc.abstractmethod
+    def item(self) -> float:
+        pass
+
+    @abc.abstractmethod
+    def __add__(self, other: Self) -> Self:
+        pass
+
+
+Extras: TypeAlias = Dict[str, jax.Array | Accumulatable]
+
 try:
     from haliax.nn.scan import BlockFoldable
 except ImportError:
@@ -53,5 +70,5 @@ def __call__(
         model: M_con,
         input: X,
         **kwargs,
-    ) -> tuple[hax.NamedArray, hax.NamedArray, dict]:
+    ) -> tuple[hax.NamedArray, hax.NamedArray, Extras]:
         ...
diff --git a/tests/test_doremi.py b/tests/test_doremi.py
index 3ad4aa9ab..e60554480 100644
--- a/tests/test_doremi.py
+++ b/tests/test_doremi.py
@@ -128,10 +128,11 @@ def test_estimate_mixture_weights():
         ds3 = LogitDataset(W3, 0.05, x3_mask, x3_bias, key=next(keys))
 
     # TODO: remove key as a requirement for models
-    def compute_loss_fn(model, example, reduction=hax.mean, reduction_axis=None, key=None):
+    def compute_loss_fn(model, example, key=None):
         del key
         y_pred = model(example.x)
-        return hax.nn.binary_cross_entropy_loss(y_pred, example.y, reduction=reduction, reduction_axis=reduction_axis)
+        losses = hax.nn.binary_cross_entropy_loss(y_pred, example.y, reduction=None)
+        return losses, hax.ones_like(losses), {}
 
     tiny_trainer_config = TrainerConfig(
         num_train_steps=300,
diff --git a/tests/test_grad_accum.py b/tests/test_grad_accum.py
index aab55c2c2..77ef4df7e 100644
--- a/tests/test_grad_accum.py
+++ b/tests/test_grad_accum.py
@@ -61,7 +61,7 @@ def scalar_loss_fn(mlp, x):
 
     mesh = Mesh(jax.devices(), ("data",))
 
-    # @hax.partitioning.named_jit(axis_resources=axis_mapping)
+    @hax.partitioning.named_jit(axis_resources=axis_mapping)
     def jit_grad_accum(mlp, x):
         grad_fn = microbatched(loss_fn, Batch, parallelism, axis_mapping, axis_mapping)
         return grad_fn(mlp, x)
diff --git a/tests/test_hf_gpt2_serialize.py b/tests/test_hf_gpt2_serialize.py
index 9cc46ca0d..29074504c 100644
--- a/tests/test_hf_gpt2_serialize.py
+++ b/tests/test_hf_gpt2_serialize.py
@@ -135,7 +135,8 @@ def torch_loss(model, input_ids) -> torch.Tensor:
 
     def compute_loss(model: LmHeadModel, input_ids):
         example = LmExample.causal(input_ids, eos_id=converter.tokenizer.eos_token_id)
-        return compute_next_token_loss(model, example, key=None).scalar()
+        loss, where, _ = compute_next_token_loss(model, example, key=None)
+        return hax.mean(loss, where=where).scalar()
 
     jax_compute_grad = equinox.filter_value_and_grad(compute_loss, has_aux=False)
     jax_grad: Gpt2LMHeadModel