diff --git a/src/levanter/checkpoint.py b/src/levanter/checkpoint.py
index ba684b8e5..1b8b7a632 100644
--- a/src/levanter/checkpoint.py
+++ b/src/levanter/checkpoint.py
@@ -157,7 +157,7 @@ def on_step(self, info, force: bool = False):
             if not force:
                 return  # don't save checkpoint at step 0 unless forced
 
-        if step == self._last_save_step:
+        if step == self._last_save_step and not force:
             # we've already saved a checkpoint at this step
             return
 
diff --git a/src/levanter/tensorstore_serialization.py b/src/levanter/tensorstore_serialization.py
index 462c1cf2c..82471e5df 100644
--- a/src/levanter/tensorstore_serialization.py
+++ b/src/levanter/tensorstore_serialization.py
@@ -1,11 +1,10 @@
 # References:
 # * Orbax: https://github.com/google/orbax/blob/11d2934ecfff77e86b5e07d0fef02b67eff4511b/orbax/checkpoint/pytree_checkpoint_handler.py#L312
-import asyncio
-import functools
 import logging
 import os
+from dataclasses import dataclass
 from functools import partial
-from typing import Callable, Optional
+from typing import Any, Callable, Optional
 
 import equinox
 import jax
@@ -13,12 +12,11 @@
 import jax.numpy as jnp
 import jax.tree_util as jtu
 import numpy as np
-import tensorstore
-from jax.sharding import Mesh
-from tensorstore import TensorStore
+from jax.sharding import Mesh, Sharding
+from jaxtyping import PyTree
 
 import haliax as hax
-import haliax.tree_util as htu
+from haliax.jax_utils import is_jax_array_like
 from haliax.partitioning import ResourceMapping
 from haliax.util import is_named_array
 
@@ -45,15 +43,23 @@ def tree_serialize_leaves_tensorstore(
     else:
         manager_was_none = False
 
-    leaf_key_paths = jax_utils.leaf_key_paths(pytree, is_leaf=_is_named_or_none)
+    leaf_key_paths = jax_utils.leaf_key_paths(pytree, is_leaf=is_named_array)
+    assert len(jax.tree.leaves(leaf_key_paths, is_leaf=is_named_array)) == len(
+        jax.tree.leaves(pytree, is_leaf=is_named_array)
+    )
 
-    def path_from_key_path(key_path):
-        return os.path.join(checkpoint_dir, *key_path.split("."))
+    paths = _fs_paths_from_key_paths(checkpoint_dir, leaf_key_paths)
 
-    paths = jtu.tree_map(path_from_key_path, leaf_key_paths, is_leaf=lambda x: x is None)
-    paths = jtu.tree_leaves(paths, is_leaf=lambda x: x is None)
-    leaves = jtu.tree_leaves(pytree, is_leaf=lambda x: x is None)
-    assert len(leaves) == len(paths)
+    # make a dataclass since tuples are pytrees
+    @dataclass
+    class Pair:
+        path: str
+        leaf: Any
+
+    zipped = jax.tree.map(lambda x, y: Pair(x, y), paths, pytree, is_leaf=lambda x: x is None)
+    paired_leaves = jax.tree.leaves(zipped)
+    paths = [p.path for p in paired_leaves]
+    leaves = [p.leaf.array if is_named_array(p.leaf) else p.leaf for p in paired_leaves]
 
     # ok, not all of these are arrays, but we'll deal with that in the async function
     def _ensure_is_array(x):
@@ -79,88 +85,40 @@ def _ensure_is_array(x):
         manager.wait_until_finished()
 
 
-def _tensorstore_spec_for(checkpoint_dir, key_path: str):
-    checkpoint_path = os.path.join(checkpoint_dir, *key_path.split("."))
-    ts_spec = array_ser.get_tensorstore_spec(checkpoint_path)
-    return ts_spec
-
+def _fs_paths_from_key_paths(checkpoint_dir, leaf_key_paths):
+    def path_from_key_path(key_path):
+        return os.path.join(checkpoint_dir, *key_path.split("."))
 
-async def _serialize_one_leaf(x, spec):
-    if isinstance(x, hax.NamedArray):
-        # we don't need to do anything special for named arrays to serialize, though we will for deserialization.
-        return await _serialize_one_leaf(x.array, spec)
-    elif isinstance(x, jax.Array):
-        if not x.is_fully_addressable:
-            return await array_ser.async_serialize(x, spec)
-        else:
-            return await save_array_to_tensorstore(x, spec)
-    elif isinstance(x, (bool, float, complex, int)):
-        return await save_array_to_tensorstore(np.array(x), spec)
-    elif x is None:
-        return
-    elif isinstance(x, jnp.ndarray):
-        return await save_array_to_tensorstore(x, spec)
-    elif isinstance(x, np.ndarray):
-        return await save_array_to_tensorstore(x, spec)
+    paths = jtu.tree_map(path_from_key_path, leaf_key_paths)
+    return paths
+
+
+def _sharding_from_leaf(leaf, axis_mapping, mesh) -> Optional[jax.sharding.Sharding]:
+    if is_named_array(leaf):
+        if leaf.array is None:
+            return None
+        return hax.partitioning.sharding_for_axis(leaf.axes, axis_mapping, mesh)
+    elif hasattr(leaf, "sharding") and getattr(leaf, "sharding") is not None:
+        return leaf.sharding
+    elif is_jax_array_like(leaf):
+        return _fully_replicated_sharding(mesh)
+    elif isinstance(leaf, (bool, float, complex, int, np.ndarray)):
+        return _fully_replicated_sharding(mesh)
     else:
-        raise TypeError(f"Can't serialize {type(x)}")
-
-
-async def save_array_to_tensorstore(x, spec):
-    if jax.process_index() == 0:
-        if x.dtype == jnp.bfloat16:
-            # Tensorstore uses 'bfloat16', not '<V2'.
-            dtype = "bfloat16"
-        else:
-            dtype = np.dtype(x.dtype).str
-        t = await tensorstore.open(
-            tensorstore.Spec(spec), create=True, shape=x.shape, dtype=dtype, context=array_ser.TS_CONTEXT
-        )
-
-        await t.write(x)
-
-
-async def load_array_from_tensorstore(spec):
-    t: TensorStore = await tensorstore.open(tensorstore.Spec(spec), context=array_ser.TS_CONTEXT)
-    return await t.read()
-
-
-async def _deserialize_one_leaf(like, spec, axis_mapping, mesh):
-    if is_named_array(like):
-        return await _deserialize_named_array(like, spec, axis_mapping, mesh)
-    elif isinstance(like, jax.Array):
-        if not like.is_fully_addressable:
-            return await array_ser.async_deserialize(like.sharding, spec, global_shape=like.shape, dtype=like.dtype)
-        else:
-            return await load_array_from_tensorstore(spec)
-    elif isinstance(like, (bool, float, complex, int)):
-        arr = await load_array_from_tensorstore(spec)
-        return arr.item()
-    elif like is None:
+        logger.warning(f"Unknown leaf type {type(leaf)}")
         return None
-    elif isinstance(like, jnp.ndarray) or isinstance(like, np.ndarray) or isinstance(like, jax.ShapeDtypeStruct):
-        return await load_array_from_tensorstore(spec)
-    elif callable(like):
-        return like
-    else:
-        raise TypeError(f"Can't deserialize {type(like)}")
 
 
-async def _deserialize_named_array(like, spec, axis_mapping, mesh):
-    # the main thing we're worried about is deserialized NamedArrays that are not yet arrays but are ShapedDtypeStructs.
-    # These don't (currently) have sharding info, but we can infer it from the axes
-    if isinstance(like.array, jax.ShapeDtypeStruct):
-        sharding = hax.partitioning.sharding_for_axis(like.axes, axis_mapping, mesh)
-        array = await array_ser.async_deserialize(sharding, spec, global_shape=like.array.shape, dtype=like.dtype)
-        assert sharding.is_equivalent_to(array.sharding, len(like.array.shape))
-        return hax.NamedArray(array, like.axes)
-    else:
-        array = await _deserialize_one_leaf(like.array, spec, axis_mapping, mesh)
-        return hax.NamedArray(array, like.axes)
+def _fully_replicated_sharding(mesh):
+    return hax.partitioning.sharding_for_axis((), {}, mesh)
 
 
 def tree_deserialize_leaves_tensorstore(
-    checkpoint_dir, pytree, axis_mapping: Optional[ResourceMapping] = None, mesh: Optional[Mesh] = None
+    checkpoint_dir,
+    pytree,
+    axis_mapping: Optional[ResourceMapping] = None,
+    mesh: Optional[Mesh] = None,
+    manager: Optional[array_ser.GlobalAsyncCheckpointManager] = None,
 ):
     """
     Deserializes a PyTree of Arrays and NamedArrays from a Tensorstore checkpoint, returning a pytree with the same shape
@@ -168,24 +126,52 @@ def tree_deserialize_leaves_tensorstore(
     (i.e. they are not yet arrays but are ShapedDtypeStructs), provided you pass in the axis_mapping and mesh (or
     they are available by context)
 
-    :param checkpoint_dir: the directory containing the tensorstore checkpoint, can be a local path or a GCS path
-    :param pytree: the exemplar pytree
-    :param axis_mapping: optional, the axis mapping for the NamedArrays (if they are not yet arrays)
-    :param mesh: optional, the mesh for the NamedArrays (if they are not yet arrays)
+    Args:
+        checkpoint_dir: the directory containing the tensorstore checkpoint, can be a local path or a GCS path
+        pytree: the exemplar pytree
+        axis_mapping: optional, the axis mapping for the NamedArrays (if they are not yet arrays)
+        mesh: optional, the mesh for the NamedArrays (if they are not yet arrays)
+        manager: optional, the checkpoint manager to use. If not provided, a new one will be created
 
-    :return: a pytree with the same shape as the exemplar pytree, but with the arrays deserialized from the checkpoint
+    Returns:
+        A pytree with the same shape as the exemplar pytree, but with the arrays deserialized from the checkpoint
     """
+    if manager is None:
+        manager = array_ser.GlobalAsyncCheckpointManager()
+
+    shardings: PyTree[Optional[Sharding]] = jtu.tree_map(
+        partial(_sharding_from_leaf, axis_mapping=axis_mapping, mesh=mesh), pytree, is_leaf=is_named_array
+    )
+
     # TODO: support ShapeDtypeStructs that are not NamedArrays
-    leaf_key_paths = jax_utils.leaf_key_paths(pytree, is_leaf=is_named_array)
-    specs = htu.tree_map(partial(_tensorstore_spec_for, checkpoint_dir), leaf_key_paths)
+    leaf_key_paths = jax_utils.leaf_key_paths(shardings, is_leaf=is_named_array)
+    paths = _fs_paths_from_key_paths(checkpoint_dir, leaf_key_paths)
+    paths = jtu.tree_leaves(paths, is_leaf=lambda x: x is None)
+
+    shardings_leaves, shardings_structure = jtu.tree_flatten(shardings, is_leaf=_is_named_or_none)
 
-    deser_partial = functools.partial(_deserialize_one_leaf, axis_mapping=axis_mapping, mesh=mesh)
+    assert len(shardings_leaves) == len(paths)
 
-    futures = jtu.tree_map(deser_partial, pytree, specs, is_leaf=is_named_array)
-    leaves, structure = jtu.tree_flatten(futures, is_leaf=is_named_array)
+    # ok, so, jax really doesn't want any Nones in the leaves here, so we need to temporarily partition the pytree
+    real_indices = [i for i, x in enumerate(shardings_leaves) if x is not None]
+    real_leaves = [x for x in shardings_leaves if x is not None]
+    real_paths = [paths[i] for i in real_indices]
 
-    async def _do_deserialize():
-        values = await asyncio.gather(*leaves)
-        return jtu.tree_unflatten(structure, values)
+    deser_leaves = manager.deserialize_with_paths(shardings=real_leaves, paths=real_paths)
+    # now we need to recreate the original structure
+
+    out_leaves = [None] * len(shardings_leaves)
+    for i, x in zip(real_indices, deser_leaves):
+        out_leaves[i] = x
+
+    deser_arrays = jtu.tree_unflatten(shardings_structure, out_leaves)
+
+    # deser_arrays only has arrays, but we need named arrays for at least some.
+    # The original pytree has the structure we want, so we'll use that to rebuild the named arrays
+    def _rebuild_named_array(like, array):
+        if is_named_array(like):
+            return hax.NamedArray(array, like.axes)
+        else:
+            return array
 
-    return asyncio.run(_do_deserialize())
+    return jtu.tree_map(_rebuild_named_array, pytree, deser_arrays, is_leaf=_is_named_or_none)
diff --git a/src/levanter/utils/jax_utils.py b/src/levanter/utils/jax_utils.py
index 1d7205365..734ec930c 100644
--- a/src/levanter/utils/jax_utils.py
+++ b/src/levanter/utils/jax_utils.py
@@ -152,17 +152,21 @@ def leaf_key_paths(
         x, prefix=join_key(prefix, p), is_leaf=is_leaf, use_state_dict_keys=use_state_dict_keys
     )
 
+    out: PyTree[str]
+
     if is_leaf is not None and is_leaf(pytree):
-        return prefix
+        out = prefix
+    elif pytree is None:
+        out = None
     elif isinstance(pytree, dict):
-        return {k: rec(v, k) for k, v in pytree.items()}
+        out = {k: rec(v, k) for k, v in pytree.items()}
     elif _isnamedtupleinstance(pytree):
         d = {k: rec(v, k) for k, v in pytree._asdict().items()}
-        return pytree.__class__(**d)
+        out = pytree.__class__(**d)
     elif isinstance(pytree, list):
-        return [rec(v, str(i)) for i, v in enumerate(pytree)]
+        out = [rec(v, str(i)) for i, v in enumerate(pytree)]
     elif isinstance(pytree, tuple):
-        return tuple(rec(v, str(i)) for i, v in enumerate(pytree))
+        out = tuple(rec(v, str(i)) for i, v in enumerate(pytree))
     elif isinstance(pytree, eqx.Module):
         names = []
         rec_values = []
@@ -170,26 +174,28 @@ def leaf_key_paths(
             if field.metadata.get("static", False):
                 continue
             field_name = field.name
-            field = getattr(pytree, field_name)
+            field_value = getattr(pytree, field_name)
             names.append(field_name)
 
             if use_state_dict_keys and hasattr(pytree, "_state_dict_key_map"):
                 field_name = pytree._state_dict_key_map().get(field_name, field_name)
 
-            rec_value = rec(field, field_name)
+            rec_value = rec(field_value, field_name)
             rec_values.append(rec_value)
 
         _, tree_def = eqx.tree_flatten_one_level(pytree)
         out = jax.tree_util.tree_unflatten(tree_def, rec_values)
-        return out
-        # this doesn't work reliably because tree_at doesn't like none values
-        # return eqx.tree_at(lambda m: [getattr(m, name) for name in names], pytree, rec_values, is_leaf=lambda x: x is None)
     else:
         leaves, treedef = jax.tree_util.tree_flatten(pytree, is_leaf=is_leaf)
-        if len(leaves) == 1:
-            return jax.tree_util.tree_unflatten(treedef, [f"{prefix}"])
+        if len(leaves) == 0:
+            out = None
+        elif len(leaves) == 1:
+            out = jax.tree_util.tree_unflatten(treedef, [f"{prefix}"])
         else:
-            return jax.tree_util.tree_unflatten(treedef, [join_key(prefix, str(i)) for i in range(len(leaves))])
+            out = jax.tree_util.tree_unflatten(treedef, [join_key(prefix, str(i)) for i in range(len(leaves))])
+
+    # assert len(jax.tree.leaves(out, is_leaf=is_leaf)) == len(jax.tree.leaves(pytree, is_leaf=is_leaf)), (out, pytree)
+    return out
 
 
 def join_key(prefix, k):
diff --git a/tests/test_checkpoint.py b/tests/test_checkpoint.py
index f5ce0f774..98e8e1d58 100644
--- a/tests/test_checkpoint.py
+++ b/tests/test_checkpoint.py
@@ -13,7 +13,7 @@
 from jax import ShapeDtypeStruct
 from jax import numpy as jnp
 
-import haliax
+import haliax as hax
 from haliax import Axis
 
 from levanter.checkpoint import (
@@ -252,7 +252,7 @@ def test_load_from_checkpoint_or_initialize():
     Out = Axis("out", 1)
 
     def init_fn(key):
-        return haliax.nn.MLP.init(In, Out, 2, 1, key=key, use_bias=False, use_final_bias=False)
+        return hax.nn.MLP.init(In, Out, 2, 1, key=key, use_bias=False, use_final_bias=False)
 
     k0 = jax.random.PRNGKey(0)
     k1 = jax.random.PRNGKey(1)
@@ -260,9 +260,9 @@ def init_fn(key):
     model0 = eqx.filter_jit(init_fn)(k0)
     model1 = eqx.filter_jit(init_fn)(k1)
 
-    is_checkpointed = jtu.tree_map(lambda _: False, model0)
+    is_checkpointed = hax.tree_util.tree_map(lambda _: False, model0)
     is_checkpointed = eqx.tree_at(lambda t: t.layers[-1], is_checkpointed, replace=True)
-    is_checkpointed1 = jtu.tree_map(lambda _: False, model1)
+    is_checkpointed1 = hax.tree_util.tree_map(lambda _: False, model1)
     is_checkpointed1 = eqx.tree_at(lambda t: t.layers[-1], is_checkpointed1, replace=True)
 
     with jax.sharding.Mesh(jax.devices(), ("devices",)), tempfile.TemporaryDirectory() as tmpdir:
@@ -306,7 +306,7 @@ def test_load_from_checkpoint_or_initialize_works_if_file_not_found():
     Out = Axis("out", 1)
 
     def init_fn(key):
-        return haliax.nn.MLP.init(In, Out, 2, 3, key=key)
+        return hax.nn.MLP.init(In, Out, 2, 3, key=key)
 
     k0 = jax.random.PRNGKey(0)
     k1 = jax.random.PRNGKey(1)
diff --git a/tests/test_export_to_hf.py b/tests/test_export_to_hf.py
index 31d44d34f..2e86900c6 100644
--- a/tests/test_export_to_hf.py
+++ b/tests/test_export_to_hf.py
@@ -41,13 +41,7 @@ def test_export_lm_to_hf():
             config = export_lm_to_hf.ConvertLmConfig(
                 checkpoint_path=f"{tmpdir}/ckpt",
                 output_dir=f"{tmpdir}/output",
-                model=export_lm_to_hf.Gpt2Config(
-                    num_layers=2,
-                    num_heads=2,
-                    seq_len=64,
-                    use_flash_attention=True,
-                    hidden_dim=32,
-                ),
+                model=model_config,
             )
             export_lm_to_hf.main(config)
 
diff --git a/tests/test_tensorstore_serialization.py b/tests/test_tensorstore_serialization.py
index 4c1854df0..77d63d656 100644
--- a/tests/test_tensorstore_serialization.py
+++ b/tests/test_tensorstore_serialization.py
@@ -46,109 +46,115 @@ def make_state(key):
 
 
 def test_checkpoint_steps():
-    key0 = jax.random.PRNGKey(0)
-    key1 = jax.random.PRNGKey(1)
+    mesh = jax.sharding.Mesh(jax.devices(), ("device",))
+    with mesh:
+        key0 = jax.random.PRNGKey(0)
+        key1 = jax.random.PRNGKey(1)
 
-    optim = optax.adam(1e-4)
+        optim = optax.adam(1e-4)
 
-    def make_state(key):
-        model = MLP(in_size=2, out_size=1, width_size=2, depth=3, key=key)
-        opt_state = optim.init(arrays_only(model))
+        def make_state(key):
+            model = MLP(in_size=2, out_size=1, width_size=2, depth=3, key=key)
+            opt_state = optim.init(arrays_only(model))
 
-        return model, opt_state, key
+            return model, opt_state, key
 
-    initial_model, initial_opt_state, initial_key = make_state(key0)
-    data = jax.random.uniform(key0, (2, 2))
+        initial_model, initial_opt_state, initial_key = make_state(key0)
+        data = jax.random.uniform(key0, (2, 2))
 
-    @eqx.filter_grad
-    def loss_fn(model, data):
-        m = jax.vmap(model)
-        return jnp.mean(jnp.square(m(data)))
+        @eqx.filter_grad
+        def loss_fn(model, data):
+            m = jax.vmap(model)
+            return jnp.mean(jnp.square(m(data)))
 
-    model, state = initial_model, initial_opt_state
-    for i in range(3):
-        grad = loss_fn(model, data)
-        updates, state = optim.update(grad, state)
-        model = eqx.apply_updates(model, updates)
+        model, state = initial_model, initial_opt_state
+        for i in range(3):
+            grad = loss_fn(model, data)
+            updates, state = optim.update(grad, state)
+            model = eqx.apply_updates(model, updates)
 
-    assert_trees_not_close(model, initial_model)
-    assert_trees_not_close(state, initial_opt_state)
+        assert_trees_not_close(model, initial_model)
+        assert_trees_not_close(state, initial_opt_state)
 
-    rep_model, rep_state, rep_key = make_state(key1)
-    assert_trees_not_close(model, rep_model)
-    assert_trees_not_close(state, rep_state)
+        rep_model, rep_state, rep_key = make_state(key1)
+        assert_trees_not_close(model, rep_model)
+        assert_trees_not_close(state, rep_state)
 
-    with TemporaryDirectory() as tmpdir:
-        tree_serialize_leaves_tensorstore(tmpdir, (model, state, initial_key, 3))
-        restored_model, restored_state, rkey, step = tree_deserialize_leaves_tensorstore(
-            tmpdir,
-            (rep_model, rep_state, rep_key, 0),
-        )
-        assert step == 3
+        with TemporaryDirectory() as tmpdir:
+            tree_serialize_leaves_tensorstore(tmpdir, (model, state, initial_key, 3))
+            restored_model, restored_state, rkey, step = tree_deserialize_leaves_tensorstore(
+                tmpdir,
+                (rep_model, rep_state, rep_key, 0),
+            )
+            assert step == 3
 
-        assert_trees_all_close(
-            jax.tree_util.tree_leaves(arrays_only(restored_model)),
-            jax.tree_util.tree_leaves(arrays_only(model)),
-        )
-        assert_trees_all_close(
-            jax.tree_util.tree_leaves(arrays_only(restored_state)),
-            jax.tree_util.tree_leaves(arrays_only(state)),
-        )
-        assert step == 3
+            assert_trees_all_close(
+                jax.tree_util.tree_leaves(arrays_only(restored_model)),
+                jax.tree_util.tree_leaves(arrays_only(model)),
+            )
+            assert_trees_all_close(
+                jax.tree_util.tree_leaves(arrays_only(restored_state)),
+                jax.tree_util.tree_leaves(arrays_only(state)),
+            )
+            assert step == 3
 
 
 def test_tensorstore_gpt2_mlp():
-    from levanter.models.gpt2 import Gpt2Mlp
+    mesh = jax.sharding.Mesh(jax.devices(), ("device",))
+    with mesh:
+        from levanter.models.gpt2 import Gpt2Mlp
 
-    key0 = jax.random.PRNGKey(0)
-    key1 = jax.random.PRNGKey(1)
+        key0 = jax.random.PRNGKey(0)
+        key1 = jax.random.PRNGKey(1)
 
-    Embed = hax.Axis("embed", 64)
-    Intermediate = hax.Axis("intermediate", 128)
+        Embed = hax.Axis("embed", 64)
+        Intermediate = hax.Axis("intermediate", 128)
 
-    def make_state(key):
-        model = Gpt2Mlp.init(Embed, Intermediate, jax.nn.relu, key=key)
-        optim = optax.adam(1e-4)
-        opt_state = optim.init(arrays_only(model))
+        def make_state(key):
+            model = Gpt2Mlp.init(Embed, Intermediate, jax.nn.relu, key=key)
+            optim = optax.adam(1e-4)
+            opt_state = optim.init(arrays_only(model))
 
-        return arrays_only(model), arrays_only(opt_state), key
+            return arrays_only(model), arrays_only(opt_state), key
 
-    initial_model, initial_opt_state, initial_key = make_state(key0)
-    rep_model, rep_state, rep_key = make_state(key1)
+        initial_model, initial_opt_state, initial_key = make_state(key0)
+        rep_model, rep_state, rep_key = make_state(key1)
 
-    assert_trees_not_close(initial_model, rep_model)
+        assert_trees_not_close(initial_model, rep_model)
 
-    with TemporaryDirectory() as tmpdir:
-        tree_serialize_leaves_tensorstore(tmpdir, (initial_model, initial_opt_state, initial_key))
-        restored_model, restored_optstate, rkey = tree_deserialize_leaves_tensorstore(
-            tmpdir,
-            (rep_model, rep_state, rep_key),
-        )
+        with TemporaryDirectory() as tmpdir:
+            tree_serialize_leaves_tensorstore(tmpdir, (initial_model, initial_opt_state, initial_key))
+            restored_model, restored_optstate, rkey = tree_deserialize_leaves_tensorstore(
+                tmpdir,
+                (rep_model, rep_state, rep_key),
+            )
 
-        assert_trees_all_close(
-            jax.tree_util.tree_leaves(arrays_only(restored_model)),
-            jax.tree_util.tree_leaves(arrays_only(initial_model)),
-        )
+            assert_trees_all_close(
+                jax.tree_util.tree_leaves(arrays_only(restored_model)),
+                jax.tree_util.tree_leaves(arrays_only(initial_model)),
+            )
 
 
 def test_tensorstore_ok_with_nones():
-    A = hax.Axis("A", 10)
-
-    class MyModule(eqx.Module):
-        a: Any
-        b: Any
-
-    m = MyModule(a=None, b=hax.zeros(A))
-    m2 = MyModule(a=None, b=hax.ones(A))
-
-    with TemporaryDirectory() as tmpdir:
-        tree_serialize_leaves_tensorstore(tmpdir, m)
-        m3 = tree_deserialize_leaves_tensorstore(tmpdir, m2)
-        assert m3.a is None
-        assert hax.all(m3.b == hax.zeros(A))
-
-    m3 = MyModule(a=hax.zeros(A), b=hax.ones(A))
-    with TemporaryDirectory() as tmpdir:
-        tree_serialize_leaves_tensorstore(tmpdir, m2)
-        with pytest.raises(ValueError):
-            tree_deserialize_leaves_tensorstore(tmpdir, m3)
+    mesh = jax.sharding.Mesh(jax.devices(), ("device",))
+    with mesh:
+        A = hax.Axis("A", 10)
+
+        class MyModule(eqx.Module):
+            a: Any
+            b: Any
+
+        m = MyModule(a=None, b=hax.zeros(A))
+        m2 = MyModule(a=None, b=hax.ones(A))
+
+        with TemporaryDirectory() as tmpdir:
+            tree_serialize_leaves_tensorstore(tmpdir, m)
+            m3 = tree_deserialize_leaves_tensorstore(tmpdir, m2)
+            assert m3.a is None
+            assert hax.all(m3.b == hax.zeros(A))
+
+        m3 = MyModule(a=hax.zeros(A), b=hax.ones(A))
+        with TemporaryDirectory() as tmpdir:
+            tree_serialize_leaves_tensorstore(tmpdir, m2)
+            with pytest.raises(ValueError):
+                tree_deserialize_leaves_tensorstore(tmpdir, m3)