diff --git a/openhtf/__init__.py b/openhtf/__init__.py
index d6b490462..84abf4536 100644
--- a/openhtf/__init__.py
+++ b/openhtf/__init__.py
@@ -15,7 +15,6 @@
 
 import importlib.metadata
 import signal
-import typing
 
 from openhtf.core import phase_executor
 from openhtf.core import test_record
diff --git a/openhtf/core/base_plugs.py b/openhtf/core/base_plugs.py
index dbfdd55a0..819a34672 100644
--- a/openhtf/core/base_plugs.py
+++ b/openhtf/core/base_plugs.py
@@ -94,7 +94,7 @@ def __init__(self, my_config_key)
 """
 
 import logging
-from typing import Any, Dict, Set, Text, Type, Union
+from typing import Any, Dict, Text, Type, Union
 
 import attr
 
@@ -128,17 +128,17 @@ def tearDown(self):
       via TestApi.
   """
   # Override this to True in subclasses to support remote Plug access.
-  enable_remote = False  # type: bool
+  enable_remote: bool = False
   # Allow explicitly disabling remote access to specific attributes.
-  disable_remote_attrs = set()  # type: Set[Text]
+  disable_remote_attrs = set()
   # Override this to True in subclasses to support using with_plugs with this
   # plug without needing to use placeholder.  This will only affect the classes
   # that explicitly define this; subclasses do not share the declaration.
-  auto_placeholder = False  # type: bool
+  auto_placeholder: bool = False
   # Default logger to be used only in __init__ of subclasses.
   # This is overwritten both on the class and the instance so don't store
   # a copy of it anywhere.
-  logger = _LOG  # type: logging.Logger
+  logger: logging.Logger = _LOG
 
   @util.classproperty
   def placeholder(cls) -> 'PlugPlaceholder':  # pylint: disable=no-self-argument
@@ -185,7 +185,7 @@ class FrontendAwareBasePlug(BasePlug, util.SubscribableStateMixin):
   Since the Station API runs in a separate thread, the _asdict() method of
   frontend-aware plugs should be written with thread safety in mind.
   """
-  enable_remote = True  # type: bool
+  enable_remote: bool = True
 
 
 @attr.s(slots=True, frozen=True)
diff --git a/openhtf/core/diagnoses_lib.py b/openhtf/core/diagnoses_lib.py
index ae1424006..f8adbf1ff 100644
--- a/openhtf/core/diagnoses_lib.py
+++ b/openhtf/core/diagnoses_lib.py
@@ -324,7 +324,6 @@ def possible_results(self) -> List[Text]:
 
   def _check_definition(self) -> None:
     """Internal function to verify that the diagnoser is completely defined."""
-    pass
 
 
 class BasePhaseDiagnoser(_BaseDiagnoser, abc.ABC):
diff --git a/openhtf/core/measurements.py b/openhtf/core/measurements.py
index 9dbbc5a6e..d7ac74c2a 100644
--- a/openhtf/core/measurements.py
+++ b/openhtf/core/measurements.py
@@ -63,7 +63,6 @@ def WidgetTestPhase(test):
 import enum
 import functools
 import logging
-import time
 import typing
 from typing import Any, Callable, Dict, Iterator, List, Optional, Text, Tuple, Union
 
diff --git a/openhtf/core/phase_collections.py b/openhtf/core/phase_collections.py
index 97a3ade36..0e0425a25 100644
--- a/openhtf/core/phase_collections.py
+++ b/openhtf/core/phase_collections.py
@@ -23,7 +23,7 @@
 import abc
 import collections
 from collections.abc import Iterable as CollectionsIterable
-from typing import Any, Callable, DefaultDict, Dict, Iterable, Iterator, List, Optional, Text, Tuple, Type, TypeVar, Union
+from typing import Any, Callable, Dict, Iterable, Iterator, List, Optional, Text, Tuple, Type, TypeVar, Union
 
 import attr
 from openhtf import util
@@ -221,16 +221,18 @@ def check_for_duplicate_subtest_names(sequence: PhaseSequence):
   Raises:
     DuplicateSubtestNamesError: when duplicate subtest names are found.
   """
-  names_to_subtests = collections.defaultdict(
-      list)  # type: DefaultDict[Text, List[Subtest]]
+  names_to_subtests: collections.defaultdict[str, list[Subtest]] = (
+      collections.defaultdict(list)
+  )
   for subtest in sequence.filter_by_type(Subtest):
     names_to_subtests[subtest.name].append(subtest)
 
-  duplicates = []  # type: List[Text]
+  duplicates: list[str] = []
   for name, subtests in names_to_subtests.items():
     if len(subtests) > 1:
-      duplicates.append('Name "{}" used by multiple subtests: {}'.format(
-          name, subtests))
+      duplicates.append(
+          'Name "{}" used by multiple subtests: {}'.format(name, subtests)
+      )
   if not duplicates:
     return
   duplicates.sort()
diff --git a/openhtf/output/callbacks/__init__.py b/openhtf/output/callbacks/__init__.py
index 467d42ebf..5463c13ce 100644
--- a/openhtf/output/callbacks/__init__.py
+++ b/openhtf/output/callbacks/__init__.py
@@ -80,8 +80,8 @@ class OutputToFile(object):
 
   def __init__(self, filename_pattern_or_file: Union[Text, Callable[..., Text],
                                                      BinaryIO]):
-    self.filename_pattern = None  # type: Optional[Union[Text, Callable[..., Text]]]
-    self.output_file = None  # type: Optional[BinaryIO]
+    self.filename_pattern: Optional[Union[Text, Callable[..., Text]]] = None
+    self.output_file: Optional[BinaryIO] = None
     if (isinstance(filename_pattern_or_file, str) or
         callable(filename_pattern_or_file)):
       self.filename_pattern = filename_pattern_or_file  # pytype: disable=annotation-type-mismatch
diff --git a/openhtf/output/servers/pub_sub.py b/openhtf/output/servers/pub_sub.py
index dc2acfdcd..b900f4b82 100644
--- a/openhtf/output/servers/pub_sub.py
+++ b/openhtf/output/servers/pub_sub.py
@@ -67,8 +67,6 @@ def on_close(self):
 
   def on_subscribe(self, info):
     """Called when new clients subscribe. Subclasses can override."""
-    pass
 
   def on_unsubscribe(self):
     """Called when clients unsubscribe. Subclasses can override."""
-    pass
diff --git a/openhtf/plugs/generic/serial_collection.py b/openhtf/plugs/generic/serial_collection.py
index 754709f2a..aa3b3a51a 100644
--- a/openhtf/plugs/generic/serial_collection.py
+++ b/openhtf/plugs/generic/serial_collection.py
@@ -58,10 +58,10 @@ class SerialCollectionPlug(base_plugs.BasePlug):
   # Serial library can raise these exceptions
   SERIAL_EXCEPTIONS = (serial.SerialException, ValueError)
 
-  _serial = None  # type: serial.Serial
-  _serial_port = None  # type: int
-  _collect = None  # type: bool
-  _collection_thread = None  # type: Optional[threading.Thread]
+  _serial: Optional[serial.Serial] = None
+  _serial_port: Optional[int] = None
+  _collect: Optional[bool] = None
+  _collection_thread: Optional[threading.Thread] = None
 
   @CONF.inject_positional_args
   def __init__(self, serial_collection_port, serial_collection_baud):
diff --git a/openhtf/plugs/user_input.py b/openhtf/plugs/user_input.py
index 0a323b9af..1d062b265 100644
--- a/openhtf/plugs/user_input.py
+++ b/openhtf/plugs/user_input.py
@@ -24,7 +24,7 @@
 import select
 import sys
 import threading
-from typing import Any, Callable, Dict, Optional, Text, Tuple, Union
+from typing import Any, Callable, Dict, Optional, Text, Union
 import uuid
 
 import attr
@@ -142,10 +142,10 @@ class UserInput(base_plugs.FrontendAwareBasePlug):
 
   def __init__(self):
     super(UserInput, self).__init__()
-    self.last_response = None  # type: Optional[Tuple[Text, Text]]
-    self._prompt = None  # type: Optional[Prompt]
-    self._console_prompt = None  # type: Optional[ConsolePrompt]
-    self._response = None  # type: Optional[Text]
+    self.last_response: Optional[tuple[str, str]] = None
+    self._prompt: Optional[Prompt] = None
+    self._console_prompt: Optional[ConsolePrompt] = None
+    self._response: Optional[Text] = None
     self._cond = threading.Condition(threading.RLock())
 
   def _asdict(self) -> Optional[Dict[Text, Any]]:
diff --git a/openhtf/util/__init__.py b/openhtf/util/__init__.py
index 4f735e33f..b21626cc7 100644
--- a/openhtf/util/__init__.py
+++ b/openhtf/util/__init__.py
@@ -18,7 +18,7 @@
 import threading
 import time
 import typing
-from typing import Any, Callable, Dict, Iterator, Optional, Text, Tuple, Type, TypeVar, Union
+from typing import Any, Callable, Dict, Iterator, Optional, Text, Tuple, TypeVar
 import weakref
 
 import attr
diff --git a/openhtf/util/logs.py b/openhtf/util/logs.py
index 6b8370258..02f9a0b6c 100644
--- a/openhtf/util/logs.py
+++ b/openhtf/util/logs.py
@@ -110,7 +110,6 @@ def MyPhase(test, helper):
 from openhtf.util import argv
 from openhtf.util import console_output
 from openhtf.util import functions
-from openhtf.util import threads
 
 # The number of v's provided as command line arguments to control verbosity.
 # Will be overridden if the ARG_PARSER below parses the -v argument.
diff --git a/openhtf/util/test.py b/openhtf/util/test.py
index 1d9d8835d..611e10cf2 100644
--- a/openhtf/util/test.py
+++ b/openhtf/util/test.py
@@ -126,7 +126,6 @@ def test_multiple(self, mock_my_plug):
   assertMeasurementFail(phase_or_test_rec, measurement)
 """
 
-import collections
 from collections.abc import Callable as CollectionsCallable, Iterator
 import functools
 import inspect
diff --git a/openhtf/util/threads.py b/openhtf/util/threads.py
index 092f5ea91..5e64cae95 100644
--- a/openhtf/util/threads.py
+++ b/openhtf/util/threads.py
@@ -13,8 +13,6 @@
 # limitations under the License.
 """Thread library defining a few helpers."""
 
-import _thread
-import contextlib
 import cProfile
 import ctypes
 import functools
diff --git a/openhtf/util/validators.py b/openhtf/util/validators.py
index 320180533..7c1d83648 100644
--- a/openhtf/util/validators.py
+++ b/openhtf/util/validators.py
@@ -71,7 +71,7 @@ def MyPhase(test: htf.TestApi) -> None:
 import math
 import numbers
 import re
-from typing import Callable, Dict, Optional, Type, TypeVar, Union
+from typing import Callable, Dict, Optional, Union
 
 from openhtf import util
 
diff --git a/openhtf/util/xmlrpcutil.py b/openhtf/util/xmlrpcutil.py
index 1f6b689c1..8e9751abb 100644
--- a/openhtf/util/xmlrpcutil.py
+++ b/openhtf/util/xmlrpcutil.py
@@ -16,7 +16,6 @@
 from collections.abc import Callable
 import http.client
 import socketserver
-import sys
 import threading
 import xmlrpc.client
 import xmlrpc.server
diff --git a/test/core/measurements_test.py b/test/core/measurements_test.py
index 17aa533cb..d1d53a4d0 100644
--- a/test/core/measurements_test.py
+++ b/test/core/measurements_test.py
@@ -19,7 +19,6 @@
 """
 
 import collections
-import unittest
 from unittest import mock
 
 import openhtf as htf
diff --git a/test/output/callbacks/callbacks_test.py b/test/output/callbacks/callbacks_test.py
index ea81ec29b..faa22326f 100644
--- a/test/output/callbacks/callbacks_test.py
+++ b/test/output/callbacks/callbacks_test.py
@@ -20,7 +20,6 @@
 
 import io
 import json
-import unittest
 
 import openhtf as htf
 from openhtf import util
diff --git a/test/output/callbacks/mfg_inspector_test.py b/test/output/callbacks/mfg_inspector_test.py
index 4f562fc20..ee19e5927 100644
--- a/test/output/callbacks/mfg_inspector_test.py
+++ b/test/output/callbacks/mfg_inspector_test.py
@@ -19,7 +19,6 @@
 """
 import collections
 import io
-import unittest
 from unittest import mock
 
 import openhtf as htf
diff --git a/test/phase_descriptor_test.py b/test/phase_descriptor_test.py
index 727513593..29c84e086 100644
--- a/test/phase_descriptor_test.py
+++ b/test/phase_descriptor_test.py
@@ -30,7 +30,6 @@
 
 def plain_func():
   """Plain Docstring."""
-  pass
 
 
 def normal_test_phase():
diff --git a/test/plugs/plugs_test.py b/test/plugs/plugs_test.py
index 6325c7084..eaaedfd63 100644
--- a/test/plugs/plugs_test.py
+++ b/test/plugs/plugs_test.py
@@ -14,7 +14,6 @@
 
 import threading
 import time
-import unittest
 
 from openhtf import plugs
 from openhtf.core import base_plugs
diff --git a/test/test_state_test.py b/test/test_state_test.py
index b7f13e7f4..1ec948934 100644
--- a/test/test_state_test.py
+++ b/test/test_state_test.py
@@ -16,7 +16,6 @@
 import logging
 import sys
 import tempfile
-import unittest
 from unittest import mock
 
 from absl.testing import parameterized
@@ -37,7 +36,6 @@
 @openhtf.PhaseOptions(name='test_phase')
 def test_phase():
   """Test docstring."""
-  pass
 
 
 PHASE_STATE_BASE_TYPE_INITIAL = {
diff --git a/test/util/text_test.py b/test/util/text_test.py
index ff684d207..f3b8edbad 100644
--- a/test/util/text_test.py
+++ b/test/util/text_test.py
@@ -17,7 +17,6 @@
 import sys
 import types
 import typing
-import unittest
 from unittest import mock
 
 from absl.testing import parameterized