diff --git a/pathwaysutils/__init__.py b/pathwaysutils/__init__.py
index 81d0427..62506f6 100644
--- a/pathwaysutils/__init__.py
+++ b/pathwaysutils/__init__.py
@@ -12,12 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 """Package of Pathways-on-Cloud utilities."""
+from collections.abc import Callable
 from pathwaysutils import _initialize
 
-initialize = _initialize.initialize
-is_pathways_backend_used = _initialize.is_pathways_backend_used
+initialize: Callable[[], None] = _initialize.initialize
+is_pathways_backend_used: Callable[[], bool] = _initialize.is_pathways_backend_used
 
 del _initialize
 
 # When changing this, also update the CHANGELOG.md.
-__version__ = "v0.1.5"
+__version__: str = "v0.1.5"
diff --git a/pathwaysutils/collect_profile.py b/pathwaysutils/collect_profile.py
index 26a01e6..57c971e 100644
--- a/pathwaysutils/collect_profile.py
+++ b/pathwaysutils/collect_profile.py
@@ -26,7 +26,7 @@
 _logger.setLevel(logging.INFO)
 
 
-_DESCRIPTION = """
+_DESCRIPTION: str = """
 To profile running JAX programs, you first need to start the profiler server
 in the program of interest. You can do this via
 `jax.profiler.start_server(<port>)`. Once the program is running and the
@@ -36,7 +36,7 @@
 """
 
 
-def _get_parser():
+def _get_parser() -> argparse.ArgumentParser:
   """Returns an argument parser for the collect_profile script."""
   parser = argparse.ArgumentParser(description=_DESCRIPTION)
   parser.add_argument(
@@ -62,7 +62,7 @@ def _get_parser():
   return parser
 
 
-def main():
+def main() -> None:
   parser = _get_parser()
   args = parser.parse_args()
 
diff --git a/pathwaysutils/experimental/reshard.py b/pathwaysutils/experimental/reshard.py
index c2cb906..9ba4f0b 100644
--- a/pathwaysutils/experimental/reshard.py
+++ b/pathwaysutils/experimental/reshard.py
@@ -14,13 +14,12 @@
 """Experimental resharding API for elastic device sets."""
 
 import base64
-import collections
-from collections.abc import Mapping
+from collections.abc import Callable, Mapping, Sequence
 import json
 import logging
 import math
 import operator
-from typing import Any, Callable, Dict, Mapping, Sequence
+from typing import Any
 
 import jax
 from pathwaysutils import jax as pw_jax
@@ -57,7 +56,7 @@ def __init__(
   ):
     def ifrt_hlo_sharding(
         aval: jax.core.ShapedArray, sharding: jax.sharding.Sharding
-    ) -> Dict[str, Any]:
+    ) -> dict[str, Any]:
       result = {
           "devices": {
               "device_ids": [
diff --git a/pathwaysutils/experimental/split_by_mesh_axis.py b/pathwaysutils/experimental/split_by_mesh_axis.py
index 06fa833..88e0e97 100644
--- a/pathwaysutils/experimental/split_by_mesh_axis.py
+++ b/pathwaysutils/experimental/split_by_mesh_axis.py
@@ -13,7 +13,8 @@
 # limitations under the License.
 """Experimental split by mesh axis API."""
 
-from typing import Any, Sequence
+from collections.abc import Sequence
+from typing import Any, cast
 
 import jax
 from pathwaysutils import jax as pw_jax
@@ -167,7 +168,8 @@ def split_by_mesh_axis(
       mesh_axis_sizes=mesh.axis_sizes,
       mesh_axis_idx=mesh_axis_idx,
       mesh_axis_sections=mesh_axis_sections,
-      submesh_shardings=submesh_shardings,
+      # TODO: b/491156211 - Remove cast once type mismatch is fixed.
+      submesh_shardings=cast(Any, submesh_shardings),
       donate=donate,
   )
 
diff --git a/pathwaysutils/lru_cache.py b/pathwaysutils/lru_cache.py
index 6608704..13cfb8a 100644
--- a/pathwaysutils/lru_cache.py
+++ b/pathwaysutils/lru_cache.py
@@ -13,15 +13,19 @@
 # limitations under the License.
 """An LRU cache that will be cleared when JAX clears its internal cache."""
 
+from collections.abc import Callable
 import functools
-from typing import Any, Callable
+from typing import Any, TypeVar
 
 from jax.extend import backend
 
 
+_F = TypeVar("_F", bound=Callable[..., Any])
+
+
 def lru_cache(
     maxsize: int = 4096,
-) -> Callable[[Callable[..., Any]], Callable[..., Any]]:
+) -> Callable[[_F], _F]:
   """An LRU cache that will be cleared when JAX clears its internal cache.
 
   Args:
@@ -32,7 +36,7 @@ def lru_cache(
     A function that can be used to decorate a function to cache its results.
   """
 
-  def wrap(f):
+  def wrap(f: _F) -> _F:
     cached = functools.lru_cache(maxsize=maxsize)(f)
     wrapper = functools.wraps(f)(cached)
 
diff --git a/pathwaysutils/persistence/helper.py b/pathwaysutils/persistence/helper.py
index 48d3021..5d8b535 100644
--- a/pathwaysutils/persistence/helper.py
+++ b/pathwaysutils/persistence/helper.py
@@ -14,10 +14,11 @@
 """Helper functions for persistence."""
 
 import base64
+from collections.abc import Sequence
 import concurrent.futures
 import datetime
 import json
-from typing import Any, Sequence, Tuple, Union
+from typing import Any
 
 import jax
 from jax import core
@@ -93,7 +94,7 @@ def get_hlo_sharding_string(
 def get_shape_info(
     dtype: np.dtype,
     dimensions: Sequence[int],
-) -> dict[str, Union[Sequence[int], str]]:
+) -> dict[str, Sequence[int] | str]:
   """Returns shape info in the format expected by read requests."""
   return {
       "xla_primitive_type_str": dtype_to_xla_primitive_type_str(dtype),
@@ -107,7 +108,7 @@ def get_write_request(
     jax_array: jax.Array,
     timeout: datetime.timedelta,
     return_dict: bool = False,
-) -> Union[str, dict[str, Any]]:
+) -> str | dict[str, Any]:
   """Returns a string representation of the plugin program which writes the given jax_array to the given location."""
   sharding = jax_array.sharding
   assert isinstance(sharding, jax.sharding.Sharding), sharding
@@ -171,7 +172,7 @@ def get_read_request(
     devices: Sequence[jax.Device],
     timeout: datetime.timedelta,
     return_dict: bool = False,
-) -> Union[str, dict[str, Any]]:
+) -> str | dict[str, Any]:
   """Returns a string representation of the plugin program which reads the given array from the given location into the provided sharding."""
   if not isinstance(devices, np.ndarray):
     devices = np.array(devices)
@@ -256,9 +257,9 @@ def read_one_array(
     dtype: np.dtype,
     shape: Sequence[int],
     shardings: jax.sharding.Sharding,
-    devices: Union[Sequence[jax.Device], np.ndarray],
+    devices: Sequence[jax.Device] | np.ndarray,
     timeout: datetime.timedelta,
-):
+) -> jax.Array:
   """Creates the read array plugin program string, compiles it to an executable, calls it and returns the result."""
   read_request = get_read_request(
       location,
@@ -284,9 +285,9 @@ def read_arrays(
     dtypes: Sequence[np.dtype],
     shapes: Sequence[Sequence[int]],
     shardings: Sequence[jax.sharding.Sharding],
-    devices: Union[Sequence[jax.Device], np.ndarray],
+    devices: Sequence[jax.Device] | np.ndarray,
     timeout: datetime.timedelta,
-) -> Tuple[Sequence[jax.Array], concurrent.futures.Future[None]]:
+) -> tuple[Sequence[jax.Array], concurrent.futures.Future[None]]:
   """Creates the read array plugin program string, compiles it to an executable, calls it and returns the result."""
 
   bulk_read_request = get_bulk_read_request(
diff --git a/pathwaysutils/plugin_executable.py b/pathwaysutils/plugin_executable.py
index 789d4b5..e1c8956 100644
--- a/pathwaysutils/plugin_executable.py
+++ b/pathwaysutils/plugin_executable.py
@@ -13,10 +13,9 @@
 # limitations under the License.
 """PluginExecutable is a class for executing plugin programs."""
 
+from collections.abc import Sequence
 import concurrent.futures
 import threading
-from typing import List, Sequence, Tuple, Union
-
 import jax
 from jax.extend import ifrt_programs
 from jax.interpreters import pxla
@@ -36,11 +35,11 @@ def __init__(self, prog_str: str):
 
   def call(
       self,
-      in_arr: Sequence[Union[jax.Array, List[jax.Array]]] = (),
+      in_arr: Sequence[jax.Array | Sequence[jax.Array]] = (),
       out_shardings: Sequence[jax.sharding.Sharding] = (),
       out_avals: Sequence[jax.core.ShapedArray] = (),
       out_committed: bool = True,
-  ) -> Tuple[Sequence[jax.Array], concurrent.futures.Future[None]]:
+  ) -> tuple[Sequence[jax.Array], concurrent.futures.Future[None]]:
     """Runs the compiled IFRT program and returns the result and a future."""
     results_with_token = self.compiled.execute_sharded(in_arr, with_tokens=True)
 
diff --git a/pathwaysutils/profiling.py b/pathwaysutils/profiling.py
index e6f2a4c..d0c5e10 100644
--- a/pathwaysutils/profiling.py
+++ b/pathwaysutils/profiling.py
@@ -19,7 +19,6 @@
 import logging
 import os
 import threading
-import time
 from typing import Any
 import urllib.parse
 
@@ -38,11 +37,11 @@ class _ProfileState:
   executable: plugin_executable.PluginExecutable | None = None
   lock: threading.Lock
 
-  def __init__(self):
+  def __init__(self) -> None:
     self.executable = None
     self.lock = threading.Lock()
 
-  def reset(self):
+  def reset(self) -> None:
     self.executable = None
 
 
@@ -52,7 +51,7 @@ def reset(self):
 _original_stop_trace = jax.profiler.stop_trace
 
 
-def toy_computation():
+def toy_computation() -> None:
   """A toy computation to run before the first profile."""
   x = jax.jit(lambda x: x + 1)(jnp.array(1))
   x.block_until_ready()
@@ -154,7 +153,7 @@ def start_trace(
   )
 
 
-def stop_trace():
+def stop_trace() -> None:
   """Stops the currently-running profiler trace."""
   try:
     with _profile_state.lock:
@@ -172,7 +171,7 @@ def stop_trace():
 _profiler_thread: threading.Thread | None = None
 
 
-def start_server(port: int):
+def start_server(port: int) -> None:
   """Starts the profiling server on port `port`.
 
   The signature is slightly different from `jax.profiler.start_server`
@@ -192,7 +191,7 @@ class ProfilingConfig:
       repository_path: str
 
     @app.post("/profiling")
-    async def profiling(pc: ProfilingConfig):  # pylint: disable=unused-variable
+    async def profiling(pc: ProfilingConfig) -> dict[str, str]:  # pylint: disable=unused-variable
       _logger.debug("Capturing profiling data for %s ms", pc.duration_ms)
       _logger.debug("Writing profiling data to %s", pc.repository_path)
       await asyncio.to_thread(jax.profiler.start_trace, pc.repository_path)
@@ -210,7 +209,7 @@ async def profiling(pc: ProfilingConfig):  # pylint: disable=unused-variable
   _profiler_thread.start()
 
 
-def stop_server():
+def stop_server() -> None:
   """Raises an error if there is no active profiler server.
 
   Pathways profiling servers are not stoppable at this time.
@@ -257,7 +256,7 @@ def collect_profile(
   return True
 
 
-def monkey_patch_jax():
+def monkey_patch_jax() -> None:
   """Monkey patches JAX with Pathways versions of functions.
 
   The signatures in patched functions should match the original.
@@ -279,7 +278,7 @@ def start_trace_patch(
       profiler_options: jax.profiler.ProfileOptions | None = None,  # pylint: disable=unused-argument
   ) -> None:
     _logger.debug("jax.profile.start_trace patched with pathways' start_trace")
-    return start_trace(
+    start_trace(
         log_dir,
         create_perfetto_link=create_perfetto_link,
         create_perfetto_trace=create_perfetto_trace,
@@ -291,21 +290,21 @@ def start_trace_patch(
 
   def stop_trace_patch() -> None:
     _logger.debug("jax.profile.stop_trace patched with pathways' stop_trace")
-    return stop_trace()
+    stop_trace()
 
   jax.profiler.stop_trace = stop_trace_patch
   jax._src.profiler.stop_trace = stop_trace_patch  # pylint: disable=protected-access
 
-  def start_server_patch(port: int):
+  def start_server_patch(port: int) -> None:
     _logger.debug(
         "jax.profile.start_server patched with pathways' start_server"
     )
-    return start_server(port)
+    start_server(port)
 
   jax.profiler.start_server = start_server_patch
 
-  def stop_server_patch():
+  def stop_server_patch() -> None:
     _logger.debug("jax.profile.stop_server patched with pathways' stop_server")
-    return stop_server()
+    stop_server()
 
   jax.profiler.stop_server = stop_server_patch
diff --git a/pathwaysutils/proxy_backend.py b/pathwaysutils/proxy_backend.py
index cc9ccce..d599f21 100644
--- a/pathwaysutils/proxy_backend.py
+++ b/pathwaysutils/proxy_backend.py
@@ -18,7 +18,7 @@
 from pathwaysutils import jax as pw_jax
 
 
-def register_backend_factory():
+def register_backend_factory() -> None:
   backend.register_backend_factory(
       "proxy",
       lambda: pw_jax.ifrt_proxy.get_client(
diff --git a/pathwaysutils/reshard.py b/pathwaysutils/reshard.py
index 496e6be..e112145 100644
--- a/pathwaysutils/reshard.py
+++ b/pathwaysutils/reshard.py
@@ -14,7 +14,8 @@
 """Resharding API using the IFRT RemapArray API."""
 
 import collections
-from typing import Any, Callable, Mapping, Sequence
+from collections.abc import Callable, Mapping, Sequence
+from typing import Any
 
 import jax
 import pathwaysutils.jax