diff --git a/ml-agents/mlagents/trainers/agent_processor.py b/ml-agents/mlagents/trainers/agent_processor.py
index 63f8561bc3..ec8d7bb0d0 100644
--- a/ml-agents/mlagents/trainers/agent_processor.py
+++ b/ml-agents/mlagents/trainers/agent_processor.py
@@ -14,7 +14,6 @@
     EnvironmentStats,
 )
 from mlagents.trainers.trajectory import Trajectory, AgentExperience
-from mlagents.trainers.policy.tf_policy import TFPolicy
 from mlagents.trainers.policy import Policy
 from mlagents.trainers.action_info import ActionInfo, ActionInfoOutputs
 from mlagents.trainers.stats import StatsReporter
@@ -32,7 +31,7 @@ class AgentProcessor:
 
     def __init__(
         self,
-        policy: TFPolicy,
+        policy: Policy,
         behavior_id: str,
         stats_reporter: StatsReporter,
         max_trajectory_length: int = sys.maxsize,
@@ -290,7 +289,7 @@ class AgentManager(AgentProcessor):
 
     def __init__(
         self,
-        policy: TFPolicy,
+        policy: Policy,
         behavior_id: str,
         stats_reporter: StatsReporter,
         max_trajectory_length: int = sys.maxsize,
diff --git a/ml-agents/mlagents/trainers/env_manager.py b/ml-agents/mlagents/trainers/env_manager.py
index 9d03db3dc7..613147b663 100644
--- a/ml-agents/mlagents/trainers/env_manager.py
+++ b/ml-agents/mlagents/trainers/env_manager.py
@@ -8,7 +8,7 @@
 )
 from mlagents_envs.side_channel.stats_side_channel import EnvironmentStats
 
-from mlagents.trainers.policy.tf_policy import TFPolicy
+from mlagents.trainers.policy import Policy
 from mlagents.trainers.agent_processor import AgentManager, AgentManagerQueue
 from mlagents.trainers.action_info import ActionInfo
 from mlagents_envs.logging_util import get_logger
@@ -36,11 +36,11 @@ def empty(worker_id: int) -> "EnvironmentStep":
 
 class EnvManager(ABC):
     def __init__(self):
-        self.policies: Dict[BehaviorName, TFPolicy] = {}
+        self.policies: Dict[BehaviorName, Policy] = {}
         self.agent_managers: Dict[BehaviorName, AgentManager] = {}
         self.first_step_infos: List[EnvironmentStep] = []
 
-    def set_policy(self, brain_name: BehaviorName, policy: TFPolicy) -> None:
+    def set_policy(self, brain_name: BehaviorName, policy: Policy) -> None:
         self.policies[brain_name] = policy
         if brain_name in self.agent_managers:
             self.agent_managers[brain_name].policy = policy
diff --git a/ml-agents/mlagents/trainers/ghost/trainer.py b/ml-agents/mlagents/trainers/ghost/trainer.py
index ecb93a838f..d473d9ac50 100644
--- a/ml-agents/mlagents/trainers/ghost/trainer.py
+++ b/ml-agents/mlagents/trainers/ghost/trainer.py
@@ -2,14 +2,13 @@
 # ## ML-Agent Learning (Ghost Trainer)
 
 from collections import defaultdict
-from typing import Deque, Dict, DefaultDict, List, cast
+from typing import Deque, Dict, DefaultDict, List
 
 import numpy as np
 
 from mlagents_envs.logging_util import get_logger
 from mlagents_envs.base_env import BehaviorSpec
 from mlagents.trainers.policy import Policy
-from mlagents.trainers.policy.tf_policy import TFPolicy
 
 from mlagents.trainers.trainer import Trainer
 from mlagents.trainers.trajectory import Trajectory
@@ -262,7 +261,7 @@ def advance(self) -> None:
         for brain_name in self._internal_policy_queues:
             internal_policy_queue = self._internal_policy_queues[brain_name]
             try:
-                policy = cast(TFPolicy, internal_policy_queue.get_nowait())
+                policy = internal_policy_queue.get_nowait()
                 self.current_policy_snapshot[brain_name] = policy.get_weights()
             except AgentManagerQueue.Empty:
                 pass
@@ -306,7 +305,7 @@ def save_model(self) -> None:
 
     def create_policy(
         self, parsed_behavior_id: BehaviorIdentifiers, behavior_spec: BehaviorSpec
-    ) -> TFPolicy:
+    ) -> Policy:
         """
         Creates policy with the wrapped trainer's create_policy function
         The first policy encountered sets the wrapped
@@ -339,7 +338,7 @@ def create_policy(
         return policy
 
     def add_policy(
-        self, parsed_behavior_id: BehaviorIdentifiers, policy: TFPolicy
+        self, parsed_behavior_id: BehaviorIdentifiers, policy: Policy
     ) -> None:
         """
         Adds policy to GhostTrainer.
@@ -350,7 +349,7 @@ def add_policy(
         self._name_to_parsed_behavior_id[name_behavior_id] = parsed_behavior_id
         self.policies[name_behavior_id] = policy
 
-    def get_policy(self, name_behavior_id: str) -> TFPolicy:
+    def get_policy(self, name_behavior_id: str) -> Policy:
         """
         Gets policy associated with name_behavior_id
         :param name_behavior_id: Fully qualified behavior name
diff --git a/ml-agents/mlagents/trainers/optimizer/optimizer.py b/ml-agents/mlagents/trainers/optimizer/optimizer.py
index 652568325c..d18e3c60ec 100644
--- a/ml-agents/mlagents/trainers/optimizer/optimizer.py
+++ b/ml-agents/mlagents/trainers/optimizer/optimizer.py
@@ -10,6 +10,9 @@ class Optimizer(abc.ABC):
     Provides methods to update the Policy.
     """
 
+    def __init__(self):
+        self.reward_signals = {}
+
     @abc.abstractmethod
     def update(self, batch: AgentBuffer, num_sequences: int) -> Dict[str, float]:
         """
diff --git a/ml-agents/mlagents/trainers/optimizer/tf_optimizer.py b/ml-agents/mlagents/trainers/optimizer/tf_optimizer.py
index b3cf8f7de7..7bd79ce141 100644
--- a/ml-agents/mlagents/trainers/optimizer/tf_optimizer.py
+++ b/ml-agents/mlagents/trainers/optimizer/tf_optimizer.py
@@ -15,6 +15,7 @@
 
 class TFOptimizer(Optimizer):  # pylint: disable=W0223
     def __init__(self, policy: TFPolicy, trainer_params: TrainerSettings):
+        super().__init__()
         self.sess = policy.sess
         self.policy = policy
         self.update_dict: Dict[str, tf.Tensor] = {}
@@ -129,7 +130,6 @@ def create_reward_signals(
         Create reward signals
         :param reward_signal_configs: Reward signal config.
         """
-        self.reward_signals = {}
         # Create reward signals
         for reward_signal, settings in reward_signal_configs.items():
             # Name reward signals by string in case we have duplicates later
diff --git a/ml-agents/mlagents/trainers/policy/policy.py b/ml-agents/mlagents/trainers/policy/policy.py
index e97e6ee7a3..03a89f8046 100644
--- a/ml-agents/mlagents/trainers/policy/policy.py
+++ b/ml-agents/mlagents/trainers/policy/policy.py
@@ -158,3 +158,15 @@ def checkpoint(self, checkpoint_path: str, settings: SerializationSettings) -> N
     @abstractmethod
     def save(self, output_filepath: str, settings: SerializationSettings) -> None:
         pass
+
+    @abstractmethod
+    def load_weights(self, values: List[np.ndarray]) -> None:
+        pass
+
+    @abstractmethod
+    def get_weights(self) -> List[np.ndarray]:
+        return []
+
+    @abstractmethod
+    def init_load_weights(self) -> None:
+        pass
diff --git a/ml-agents/mlagents/trainers/policy/tf_policy.py b/ml-agents/mlagents/trainers/policy/tf_policy.py
index da6580c0a8..b7c460c35f 100644
--- a/ml-agents/mlagents/trainers/policy/tf_policy.py
+++ b/ml-agents/mlagents/trainers/policy/tf_policy.py
@@ -376,62 +376,6 @@ def fill_eval_dict(self, feed_dict, batched_step_result):
             feed_dict[self.action_masks] = mask
         return feed_dict
 
-    def make_empty_memory(self, num_agents):
-        """
-        Creates empty memory for use with RNNs
-        :param num_agents: Number of agents.
-        :return: Numpy array of zeros.
-        """
-        return np.zeros((num_agents, self.m_size), dtype=np.float32)
-
-    def save_memories(
-        self, agent_ids: List[str], memory_matrix: Optional[np.ndarray]
-    ) -> None:
-        if memory_matrix is None:
-            return
-        for index, agent_id in enumerate(agent_ids):
-            self.memory_dict[agent_id] = memory_matrix[index, :]
-
-    def retrieve_memories(self, agent_ids: List[str]) -> np.ndarray:
-        memory_matrix = np.zeros((len(agent_ids), self.m_size), dtype=np.float32)
-        for index, agent_id in enumerate(agent_ids):
-            if agent_id in self.memory_dict:
-                memory_matrix[index, :] = self.memory_dict[agent_id]
-        return memory_matrix
-
-    def remove_memories(self, agent_ids):
-        for agent_id in agent_ids:
-            if agent_id in self.memory_dict:
-                self.memory_dict.pop(agent_id)
-
-    def make_empty_previous_action(self, num_agents):
-        """
-        Creates empty previous action for use with RNNs and discrete control
-        :param num_agents: Number of agents.
-        :return: Numpy array of zeros.
-        """
-        return np.zeros((num_agents, self.num_branches), dtype=np.int)
-
-    def save_previous_action(
-        self, agent_ids: List[str], action_matrix: Optional[np.ndarray]
-    ) -> None:
-        if action_matrix is None:
-            return
-        for index, agent_id in enumerate(agent_ids):
-            self.previous_action_dict[agent_id] = action_matrix[index, :]
-
-    def retrieve_previous_action(self, agent_ids: List[str]) -> np.ndarray:
-        action_matrix = np.zeros((len(agent_ids), self.num_branches), dtype=np.int)
-        for index, agent_id in enumerate(agent_ids):
-            if agent_id in self.previous_action_dict:
-                action_matrix[index, :] = self.previous_action_dict[agent_id]
-        return action_matrix
-
-    def remove_previous_action(self, agent_ids):
-        for agent_id in agent_ids:
-            if agent_id in self.previous_action_dict:
-                self.previous_action_dict.pop(agent_id)
-
     def get_current_step(self):
         """
         Gets current model step.
diff --git a/ml-agents/mlagents/trainers/ppo/trainer.py b/ml-agents/mlagents/trainers/ppo/trainer.py
index aa6927fd1a..fda790064a 100644
--- a/ml-agents/mlagents/trainers/ppo/trainer.py
+++ b/ml-agents/mlagents/trainers/ppo/trainer.py
@@ -10,6 +10,7 @@
 from mlagents_envs.logging_util import get_logger
 from mlagents_envs.base_env import BehaviorSpec
 from mlagents.trainers.trainer.rl_trainer import RLTrainer
+from mlagents.trainers.policy import Policy
 from mlagents.trainers.policy.tf_policy import TFPolicy
 from mlagents.trainers.ppo.optimizer import PPOOptimizer
 from mlagents.trainers.trajectory import Trajectory
@@ -51,7 +52,7 @@ def __init__(
         )
         self.load = load
         self.seed = seed
-        self.policy: TFPolicy = None  # type: ignore
+        self.policy: Policy = None  # type: ignore
 
     def _process_trajectory(self, trajectory: Trajectory) -> None:
         """
@@ -208,7 +209,7 @@ def create_policy(
         return policy
 
     def add_policy(
-        self, parsed_behavior_id: BehaviorIdentifiers, policy: TFPolicy
+        self, parsed_behavior_id: BehaviorIdentifiers, policy: Policy
     ) -> None:
         """
         Adds policy to trainer.
@@ -224,13 +225,15 @@ def add_policy(
             )
         self.policy = policy
         self.policies[parsed_behavior_id.behavior_id] = policy
-        self.optimizer = PPOOptimizer(self.policy, self.trainer_settings)
+        self.optimizer = PPOOptimizer(
+            cast(TFPolicy, self.policy), self.trainer_settings
+        )
         for _reward_signal in self.optimizer.reward_signals.keys():
             self.collected_rewards[_reward_signal] = defaultdict(lambda: 0)
         # Needed to resume loads properly
         self.step = policy.get_current_step()
 
-    def get_policy(self, name_behavior_id: str) -> TFPolicy:
+    def get_policy(self, name_behavior_id: str) -> Policy:
         """
         Gets policy from trainer associated with name_behavior_id
         :param name_behavior_id: full identifier of policy
diff --git a/ml-agents/mlagents/trainers/sac/trainer.py b/ml-agents/mlagents/trainers/sac/trainer.py
index 0eac648617..cdaab0de40 100644
--- a/ml-agents/mlagents/trainers/sac/trainer.py
+++ b/ml-agents/mlagents/trainers/sac/trainer.py
@@ -13,6 +13,7 @@
 from mlagents_envs.timers import timed
 from mlagents_envs.base_env import BehaviorSpec
 from mlagents.trainers.policy.tf_policy import TFPolicy
+from mlagents.trainers.policy import Policy
 from mlagents.trainers.sac.optimizer import SACOptimizer
 from mlagents.trainers.trainer.rl_trainer import RLTrainer
 from mlagents.trainers.trajectory import Trajectory, SplitObservations
@@ -57,7 +58,7 @@ def __init__(
 
         self.load = load
         self.seed = seed
-        self.policy: TFPolicy = None  # type: ignore
+        self.policy: Policy = None  # type: ignore
         self.optimizer: SACOptimizer = None  # type: ignore
         self.hyperparameters: SACSettings = cast(
             SACSettings, trainer_settings.hyperparameters
@@ -312,7 +313,7 @@ def _update_reward_signals(self) -> None:
                 self._stats_reporter.add_stat(stat, np.mean(stat_list))
 
     def add_policy(
-        self, parsed_behavior_id: BehaviorIdentifiers, policy: TFPolicy
+        self, parsed_behavior_id: BehaviorIdentifiers, policy: Policy
     ) -> None:
         """
         Adds policy to trainer.
@@ -326,7 +327,9 @@ def add_policy(
             )
         self.policy = policy
         self.policies[parsed_behavior_id.behavior_id] = policy
-        self.optimizer = SACOptimizer(self.policy, self.trainer_settings)
+        self.optimizer = SACOptimizer(
+            cast(TFPolicy, self.policy), self.trainer_settings
+        )
         for _reward_signal in self.optimizer.reward_signals.keys():
             self.collected_rewards[_reward_signal] = defaultdict(lambda: 0)
         # Needed to resume loads properly
@@ -337,7 +340,7 @@ def add_policy(
             max(1, self.step / self.reward_signal_steps_per_update)
         )
 
-    def get_policy(self, name_behavior_id: str) -> TFPolicy:
+    def get_policy(self, name_behavior_id: str) -> Policy:
         """
         Gets policy from trainer associated with name_behavior_id
         :param name_behavior_id: full identifier of policy
diff --git a/ml-agents/mlagents/trainers/trainer/rl_trainer.py b/ml-agents/mlagents/trainers/trainer/rl_trainer.py
index a55d93b8c9..2ab44bcf1f 100644
--- a/ml-agents/mlagents/trainers/trainer/rl_trainer.py
+++ b/ml-agents/mlagents/trainers/trainer/rl_trainer.py
@@ -12,7 +12,7 @@
 )
 from mlagents_envs.logging_util import get_logger
 from mlagents_envs.timers import timed
-from mlagents.trainers.optimizer.tf_optimizer import TFOptimizer
+from mlagents.trainers.optimizer import Optimizer
 from mlagents.trainers.buffer import AgentBuffer
 from mlagents.trainers.trainer import Trainer
 from mlagents.trainers.components.reward_signals import RewardSignalResult
@@ -56,7 +56,7 @@ def end_episode(self) -> None:
             for agent_id in rewards:
                 rewards[agent_id] = 0
 
-    def _update_end_episode_stats(self, agent_id: str, optimizer: TFOptimizer) -> None:
+    def _update_end_episode_stats(self, agent_id: str, optimizer: Optimizer) -> None:
         for name, rewards in self.collected_rewards.items():
             if name == "environment":
                 self.stats_reporter.add_stat(
diff --git a/ml-agents/mlagents/trainers/trainer/trainer.py b/ml-agents/mlagents/trainers/trainer/trainer.py
index 4662b2f5de..dd8ca81ed3 100644
--- a/ml-agents/mlagents/trainers/trainer/trainer.py
+++ b/ml-agents/mlagents/trainers/trainer/trainer.py
@@ -5,7 +5,6 @@
 
 from mlagents_envs.logging_util import get_logger
 from mlagents_envs.base_env import BehaviorSpec
-from mlagents.trainers.policy.tf_policy import TFPolicy
 from mlagents.trainers.stats import StatsReporter
 from mlagents.trainers.trajectory import Trajectory
 from mlagents.trainers.agent_processor import AgentManagerQueue
@@ -47,7 +46,7 @@ def __init__(
         self.step: int = 0
         self.artifact_path = artifact_path
         self.summary_freq = self.trainer_settings.summary_freq
-        self.policies: Dict[str, TFPolicy] = {}
+        self.policies: Dict[str, Policy] = {}
 
     @property
     def stats_reporter(self):
@@ -125,7 +124,7 @@ def end_episode(self):
     @abc.abstractmethod
     def create_policy(
         self, parsed_behavior_id: BehaviorIdentifiers, behavior_spec: BehaviorSpec
-    ) -> TFPolicy:
+    ) -> Policy:
         """
         Creates policy
         """
@@ -133,7 +132,7 @@ def create_policy(
 
     @abc.abstractmethod
     def add_policy(
-        self, parsed_behavior_id: BehaviorIdentifiers, policy: TFPolicy
+        self, parsed_behavior_id: BehaviorIdentifiers, policy: Policy
     ) -> None:
         """
         Adds policy to trainer.
@@ -141,7 +140,7 @@ def add_policy(
         pass
 
     @abc.abstractmethod
-    def get_policy(self, name_behavior_id: str) -> TFPolicy:
+    def get_policy(self, name_behavior_id: str) -> Policy:
         """
         Gets policy from trainer.
         """