diff --git a/python/ray/train/_internal/session.py b/python/ray/train/_internal/session.py
index f9bedd889efbf..a623dc449a458 100644
--- a/python/ray/train/_internal/session.py
+++ b/python/ray/train/_internal/session.py
@@ -17,15 +17,13 @@
 from ray.data import Dataset, DatasetPipeline
 from ray.train._internal.accelerator import Accelerator
 from ray.train.constants import (
-    DATE,
     DETAILED_AUTOFILLED_KEYS,
-    HOSTNAME,
-    NODE_IP,
-    PID,
+    WORKER_HOSTNAME,
+    WORKER_NODE_IP,
+    WORKER_PID,
     TIME_THIS_ITER_S,
     TIME_TOTAL_S,
     TIMESTAMP,
-    TRAINING_ITERATION,
     CHECKPOINT_METADATA_KEY,
 )
 from ray.train.error import SessionMisuseError
@@ -229,14 +227,11 @@ def _auto_fill_metrics(self, result: dict) -> dict:
         self.last_report_time = current_time
 
         auto_filled_metrics = {
-            DATE: current_datetime.strftime("%Y-%m-%d_%H-%M-%S"),
             TIMESTAMP: int(time.mktime(current_datetime.timetuple())),
-            TIME_THIS_ITER_S: time_this_iter,
             TIME_TOTAL_S: self.time_total,
-            PID: os.getpid(),
-            HOSTNAME: platform.node(),
-            NODE_IP: self.local_ip,
-            TRAINING_ITERATION: self.iteration,
+            WORKER_PID: os.getpid(),
+            WORKER_HOSTNAME: platform.node(),
+            WORKER_NODE_IP: self.local_ip,
         }
 
         if not self.detailed_autofilled_metrics:
diff --git a/python/ray/train/constants.py b/python/ray/train/constants.py
index abb9e3cffb26c..71b499befeb0d 100644
--- a/python/ray/train/constants.py
+++ b/python/ray/train/constants.py
@@ -16,21 +16,22 @@
 )
 
 # Autofilled session.report() metrics. Keys should be consistent with Tune.
-TIMESTAMP = "_timestamp"
-TIME_THIS_ITER_S = "_time_this_iter_s"
-TRAINING_ITERATION = "_training_iteration"
+# The train provided `TIME_THIS_ITER_S` and `TIMESTAMP` will triumph what's
+# auto-filled by Tune session.
+# TODO: Combine the following two with tune's, once there is a centralized
+#  file for both tune/train constants.
+TIMESTAMP = "timestamp"
+TIME_THIS_ITER_S = "time_this_iter_s"
 
-BASIC_AUTOFILLED_KEYS = {TIMESTAMP, TIME_THIS_ITER_S, TRAINING_ITERATION}
-
-DATE = "_date"
-HOSTNAME = "_hostname"
-NODE_IP = "_node_ip"
-PID = "_pid"
 TIME_TOTAL_S = "_time_total_s"
 
+WORKER_HOSTNAME = "_hostname"
+WORKER_NODE_IP = "_node_ip"
+WORKER_PID = "_pid"
+
 # Will not be reported unless ENABLE_DETAILED_AUTOFILLED_METRICS_ENV
 # env var is not 0
-DETAILED_AUTOFILLED_KEYS = {DATE, HOSTNAME, NODE_IP, PID, TIME_TOTAL_S}
+DETAILED_AUTOFILLED_KEYS = {WORKER_HOSTNAME, WORKER_NODE_IP, WORKER_PID, TIME_TOTAL_S}
 
 # Default filename for JSON logger
 RESULT_FILE_JSON = "results.json"
diff --git a/python/ray/train/tests/test_examples.py b/python/ray/train/tests/test_examples.py
index 11918e449213c..ca0d6a6efbe49 100644
--- a/python/ray/train/tests/test_examples.py
+++ b/python/ray/train/tests/test_examples.py
@@ -1,7 +1,7 @@
 import pytest
 
 from ray.air.config import ScalingConfig
-from ray.train.constants import TRAINING_ITERATION
+from ray.tune.result import TRAINING_ITERATION
 
 from ray.train.examples.horovod.horovod_example import (
     train_func as horovod_torch_train_func,
diff --git a/python/ray/train/tests/test_gpu_examples.py b/python/ray/train/tests/test_gpu_examples.py
index 567c5967f91b2..6f506b5bdb920 100644
--- a/python/ray/train/tests/test_gpu_examples.py
+++ b/python/ray/train/tests/test_gpu_examples.py
@@ -4,7 +4,6 @@
 from ray.air import Checkpoint, session
 
 from ray.air.config import ScalingConfig
-from ray.train.constants import TRAINING_ITERATION
 from ray.train.examples.horovod.horovod_example import (
     train_func as horovod_torch_train_func,
 )
@@ -21,6 +20,7 @@
 )
 from ray.train.tensorflow.tensorflow_trainer import TensorflowTrainer
 from ray.train.torch.torch_trainer import TorchTrainer
+from ray.tune.result import TRAINING_ITERATION
 
 
 def test_tensorflow_mnist_gpu(ray_start_4_cpus_2_gpus):
diff --git a/python/ray/train/tests/test_mosaic_trainer.py b/python/ray/train/tests/test_mosaic_trainer.py
index fa11b2227a4de..59d1c88a0284b 100644
--- a/python/ray/train/tests/test_mosaic_trainer.py
+++ b/python/ray/train/tests/test_mosaic_trainer.py
@@ -6,9 +6,10 @@
 import torchvision
 from torchvision import transforms, datasets
 
+from ray.air import session
 from ray.air.config import ScalingConfig
 import ray.train as train
-from ray.air import session
+from ray.tune.result import TRAINING_ITERATION
 
 
 scaling_config = ScalingConfig(num_workers=2, use_gpu=False)
@@ -89,7 +90,7 @@ def test_mosaic_cifar10(ray_start_4_cpus):
     assert result["epoch"][result.index[-1]] == 4
 
     # check train_iterations
-    assert result["_training_iteration"][result.index[-1]] == 5
+    assert result[TRAINING_ITERATION][result.index[-1]] == 5
 
     # check metrics/train/Accuracy has increased
     acc = list(result["metrics/train/Accuracy"])
diff --git a/python/ray/tune/result.py b/python/ray/tune/result.py
index 04abc42a2449a..a62729a122c1e 100644
--- a/python/ray/tune/result.py
+++ b/python/ray/tune/result.py
@@ -32,9 +32,6 @@
 # (Optional) Mean loss for training iteration
 MEAN_LOSS = "mean_loss"
 
-# (Optional) Mean loss for training iteration
-NEG_MEAN_LOSS = "neg_mean_loss"
-
 # (Optional) Mean accuracy for training iteration
 MEAN_ACCURACY = "mean_accuracy"
 
@@ -44,6 +41,10 @@
 # (Optional/Auto-filled) Accumulated number of episodes for this trial.
 EPISODES_TOTAL = "episodes_total"
 
+# The timestamp of when the result is generated.
+# Default to when the result is processed by tune.
+TIMESTAMP = "timestamp"
+
 # Number of timesteps in this iteration.
 TIMESTEPS_THIS_ITER = "timesteps_this_iter"
 
@@ -67,7 +68,6 @@
 DEFAULT_RESULT_KEYS = (
     TRAINING_ITERATION,
     TIME_TOTAL_S,
-    TIMESTEPS_TOTAL,
     MEAN_ACCURACY,
     MEAN_LOSS,
 )
@@ -77,7 +77,7 @@
     TRIAL_ID,
     "experiment_id",
     "date",
-    "timestamp",
+    TIMESTAMP,
     PID,
     HOSTNAME,
     NODE_IP,
@@ -95,14 +95,12 @@
     PID,
     TIME_TOTAL_S,
     TIME_THIS_ITER_S,
-    "timestamp",
-    "experiment_id",
+    TIMESTAMP,
     "date",
     "time_since_restore",
-    "iterations_since_restore",
     "timesteps_since_restore",
+    "iterations_since_restore",
     "config",
-    "warmup_time",
 )
 
 # __duplicate__ is a magic keyword used internally to
diff --git a/python/ray/tune/tests/test_api.py b/python/ray/tune/tests/test_api.py
index 5467fb763602e..3e75ebfad7daa 100644
--- a/python/ray/tune/tests/test_api.py
+++ b/python/ray/tune/tests/test_api.py
@@ -156,7 +156,6 @@ def _function_trainable(config, reporter):
             "time_since_restore",
             "experiment_id",
             "date",
-            "warmup_time",
         }
 
         self.assertEqual(len(class_output), len(results))
@@ -871,7 +870,7 @@ def testReportTimeStep(self):
         results1 = [dict(mean_accuracy=5, done=i == 99) for i in range(100)]
         logs1, _ = self.checkAndReturnConsistentLogs(results1)
 
-        self.assertTrue(all(log[TIMESTEPS_TOTAL] is None for log in logs1))
+        self.assertTrue(all(TIMESTEPS_TOTAL not in log for log in logs1))
 
         # Test that no timesteps_this_iter are logged if only timesteps_total
         # are returned.
@@ -891,7 +890,8 @@ def testReportTimeStep(self):
         self.assertFalse(any(hasattr(log, TIMESTEPS_THIS_ITER) for log in logs2))
 
         # Test that timesteps_total and episodes_total are reported when
-        # timesteps_this_iter and episodes_this_iter despite only return zeros.
+        # timesteps_this_iter and episodes_this_iter are provided by user,
+        # despite only return zeros.
         results3 = [
             dict(timesteps_this_iter=0, episodes_this_iter=0) for i in range(10)
         ]
diff --git a/python/ray/tune/trainable/trainable.py b/python/ray/tune/trainable/trainable.py
index fb1558d8366af..6af9f93eb5c3b 100644
--- a/python/ray/tune/trainable/trainable.py
+++ b/python/ray/tune/trainable/trainable.py
@@ -7,7 +7,6 @@
 import sys
 import tempfile
 import time
-import uuid
 from contextlib import redirect_stderr, redirect_stdout
 from datetime import datetime
 from typing import Any, Callable, Dict, List, Optional, Union, Type, TYPE_CHECKING
@@ -35,6 +34,7 @@
     STDOUT_FILE,
     TIME_THIS_ITER_S,
     TIME_TOTAL_S,
+    TIMESTAMP,
     TIMESTEPS_THIS_ITER,
     TIMESTEPS_TOTAL,
     TRAINING_ITERATION,
@@ -133,7 +133,6 @@ def __init__(
             sync_timeout: Timeout after which sync processes are aborted.
         """
 
-        self._experiment_id = uuid.uuid4().hex
         self.config = config or {}
         trial_info = self.config.pop(TRIAL_INFO, None)
 
@@ -164,10 +163,10 @@ def __init__(
         self._stdout_file = stdout_file
         self._stderr_file = stderr_file
 
-        start_time = time.time()
+        self._start_time = time.time()
         self._local_ip = ray.util.get_node_ip_address()
         self.setup(copy.deepcopy(self.config))
-        setup_time = time.time() - start_time
+        setup_time = time.time() - self._start_time
         if setup_time > SETUP_TIME_THRESHOLD:
             logger.info(
                 "Trainable.setup took {:.3f} seconds. If your "
@@ -176,8 +175,6 @@ def __init__(
                 "overheads.".format(setup_time)
             )
         log_sys_usage = self.config.get("log_sys_usage", False)
-        self._start_time = start_time
-        self._warmup_time = None
         self._monitor = UtilMonitor(start=log_sys_usage)
 
         self.remote_checkpoint_dir = remote_checkpoint_dir
@@ -240,6 +237,7 @@ def get_auto_filled_metrics(
         self,
         now: Optional[datetime] = None,
         time_this_iter: Optional[float] = None,
+        timestamp: Optional[int] = None,
         debug_metrics_only: bool = False,
     ) -> dict:
         """Return a dict with metrics auto-filled by the trainable.
@@ -252,9 +250,8 @@ def get_auto_filled_metrics(
             now = datetime.today()
         autofilled = {
             TRIAL_ID: self.trial_id,
-            "experiment_id": self._experiment_id,
             "date": now.strftime("%Y-%m-%d_%H-%M-%S"),
-            "timestamp": int(time.mktime(now.timetuple())),
+            "timestamp": timestamp if timestamp else int(time.mktime(now.timetuple())),
             TIME_THIS_ITER_S: time_this_iter,
             TIME_TOTAL_S: self._time_total,
             PID: os.getpid(),
@@ -262,10 +259,11 @@ def get_auto_filled_metrics(
             NODE_IP: self._local_ip,
             "config": self.config,
             "time_since_restore": self._time_since_restore,
-            "timesteps_since_restore": self._timesteps_since_restore,
             "iterations_since_restore": self._iterations_since_restore,
-            "warmup_time": self._warmup_time,
         }
+        if self._timesteps_since_restore:
+            autofilled["timesteps_since_restore"] = self._timesteps_since_restore
+
         if debug_metrics_only:
             autofilled = {k: v for k, v in autofilled.items() if k in DEBUG_METRICS}
         return autofilled
@@ -334,10 +332,6 @@ def train(self):
             `time_total_s` (float): Accumulated time in seconds for this
             entire experiment.
 
-            `experiment_id` (str): Unique string identifier
-            for this experiment. This id is preserved
-            across checkpoint / restore calls.
-
             `training_iteration` (int): The index of this
             training iteration, e.g. call to train(). This is incremented
             after `step()` is called.
@@ -347,7 +341,7 @@ def train(self):
             `date` (str): A formatted date of when the result was processed.
 
             `timestamp` (str): A UNIX timestamp of when the result
-            was processed.
+            was processed. This may be overridden.
 
             `hostname` (str): Hostname of the machine hosting the training
             process.
@@ -358,8 +352,6 @@ def train(self):
         Returns:
             A dict that describes training progress.
         """
-        if self._warmup_time is None:
-            self._warmup_time = time.time() - self._start_time
         start = time.time()
         try:
             result = self.step()
@@ -385,9 +377,11 @@ def train(self):
         self._time_total += time_this_iter
         self._time_since_restore += time_this_iter
 
+        result_timestamp = result.get(TIMESTAMP, None)
+
         result.setdefault(DONE, False)
 
-        # self._timesteps_total should only be tracked if increments provided
+        # self._timesteps_total should only be tracked if increments are provided
         if result.get(TIMESTEPS_THIS_ITER) is not None:
             if self._timesteps_total is None:
                 self._timesteps_total = 0
@@ -401,16 +395,18 @@ def train(self):
             self._episodes_total += result[EPISODES_THIS_ITER]
 
         # self._timesteps_total should not override user-provided total
-        result.setdefault(TIMESTEPS_TOTAL, self._timesteps_total)
-        result.setdefault(EPISODES_TOTAL, self._episodes_total)
+        if self._timesteps_total is not None:
+            result.setdefault(TIMESTEPS_TOTAL, self._timesteps_total)
+        if self._episodes_total is not None:
+            result.setdefault(EPISODES_TOTAL, self._episodes_total)
         result.setdefault(TRAINING_ITERATION, self._iteration)
 
-        # Provides auto-filled neg_mean_loss for avoiding regressions
-        if result.get("mean_loss"):
-            result.setdefault("neg_mean_loss", -result["mean_loss"])
-
         now = datetime.today()
-        result.update(self.get_auto_filled_metrics(now, time_this_iter))
+        result.update(
+            self.get_auto_filled_metrics(
+                now=now, time_this_iter=time_this_iter, timestamp=result_timestamp
+            )
+        )
 
         monitor_data = self._monitor.get_data()
         if monitor_data:
@@ -429,7 +425,6 @@ def train(self):
 
     def get_state(self):
         return {
-            "experiment_id": self._experiment_id,
             "iteration": self._iteration,
             "timesteps_total": self._timesteps_total,
             "time_total": self._time_total,
@@ -774,7 +769,6 @@ def restore(
             to_load = os.path.join(checkpoint_dir, relative_checkpoint_path)
 
         # Set metadata
-        self._experiment_id = metadata["experiment_id"]
         self._iteration = metadata["iteration"]
         self._timesteps_total = metadata["timesteps_total"]
         self._time_total = metadata["time_total"]
diff --git a/rllib/algorithms/algorithm.py b/rllib/algorithms/algorithm.py
index 05c386e603846..b26a6085cb6a4 100644
--- a/rllib/algorithms/algorithm.py
+++ b/rllib/algorithms/algorithm.py
@@ -2360,12 +2360,13 @@ def get_auto_filled_metrics(
         self,
         now: Optional[datetime] = None,
         time_this_iter: Optional[float] = None,
+        timestamp: Optional[int] = None,
         debug_metrics_only: bool = False,
     ) -> dict:
         # Override this method to make sure, the `config` key of the returned results
         # contains the proper Tune config dict (instead of an AlgorithmConfig object).
         auto_filled = super().get_auto_filled_metrics(
-            now, time_this_iter, debug_metrics_only
+            now, time_this_iter, timestamp, debug_metrics_only
         )
         if "config" not in auto_filled:
             raise KeyError("`config` key not found in auto-filled results dict!")
diff --git a/rllib/utils/test_utils.py b/rllib/utils/test_utils.py
index 5f21b836fb851..207b9820cf63d 100644
--- a/rllib/utils/test_utils.py
+++ b/rllib/utils/test_utils.py
@@ -634,7 +634,6 @@ def check_train_results(train_results: PartialAlgorithmConfigDict) -> ResultDict
         "episode_reward_max",
         "episode_reward_mean",
         "episode_reward_min",
-        "episodes_total",
         "hist_stats",
         "info",
         "iterations_since_restore",
@@ -646,7 +645,6 @@ def check_train_results(train_results: PartialAlgorithmConfigDict) -> ResultDict
         "sampler_perf",
         "time_since_restore",
         "time_this_iter_s",
-        "timesteps_since_restore",
         "timesteps_total",
         "timers",
         "time_total_s",