diff --git a/.github/workflows/basic.yml b/.github/workflows/basic.yml
index 8a3f6aecb..a744f84bf 100644
--- a/.github/workflows/basic.yml
+++ b/.github/workflows/basic.yml
@@ -88,7 +88,7 @@ jobs:
           mv libensemble/tests/.cov* .
 
       - name: Upload coverage reports to Codecov
-        uses: codecov/codecov-action@v6
+        uses: codecov/codecov-action@v7
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
@@ -98,4 +98,4 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-      - uses: crate-ci/typos@v1.47.1
+      - uses: crate-ci/typos@v1.47.2
diff --git a/.github/workflows/extra.yml b/.github/workflows/extra.yml
index 16a4213ad..f3de20e98 100644
--- a/.github/workflows/extra.yml
+++ b/.github/workflows/extra.yml
@@ -101,7 +101,7 @@ jobs:
           mv libensemble/tests/.cov* .
 
       - name: Upload coverage reports to Codecov
-        uses: codecov/codecov-action@v6
+        uses: codecov/codecov-action@v7
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
@@ -111,4 +111,4 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-      - uses: crate-ci/typos@v1.47.1
+      - uses: crate-ci/typos@v1.47.2
diff --git a/docs/examples/calling_scripts.rst b/docs/examples/calling_scripts.rst
index 7a58ad05e..269fe1d3c 100644
--- a/docs/examples/calling_scripts.rst
+++ b/docs/examples/calling_scripts.rst
@@ -47,6 +47,6 @@ paired with a gest-api ``simulator`` callable.
     :language: python
     :caption: tests/regression_tests/test_asktell_aposmm_nlopt.py
     :linenos:
-    :end-at: workflow.exit_criteria = ExitCriteria(sim_max=2000, wallclock_max=600)
+    :end-at: H, _, _ = workflow.run(sim_max=3000, wallclock_max=600)
 
 .. _regression tests: https://github.com/Libensemble/libensemble/tree/develop/libensemble/tests/regression_tests
diff --git a/docs/platforms/aurora.rst b/docs/platforms/aurora.rst
index c29ed0bc0..a2f652f3a 100644
--- a/docs/platforms/aurora.rst
+++ b/docs/platforms/aurora.rst
@@ -56,8 +56,8 @@ simulations for each worker:
 
 .. code-block:: python
 
-    # Instruct libEnsemble to exit after this many simulations
-    ensemble.exit_criteria = ExitCriteria(sim_max=nsim_workers * 2)
+    # Run ensemble; exit after this many simulations
+    ensemble.run(sim_max=nsim_workers * 2)
 
 Now grab an interactive session on two nodes (or use the batch script at
 ``../submission_scripts/submit_pbs_aurora.sh``)::
diff --git a/docs/tutorials/aposmm_tutorial.rst b/docs/tutorials/aposmm_tutorial.rst
index 7cc0d7b9f..094a7c1f6 100644
--- a/docs/tutorials/aposmm_tutorial.rst
+++ b/docs/tutorials/aposmm_tutorial.rst
@@ -105,7 +105,7 @@ libEnsemble classes, APOSMM, and our simulator callable:
     from libensemble import Ensemble
     from libensemble.gen_classes import APOSMM
     from gest_api.vocs import VOCS
-    from libensemble.specs import SimSpecs, GenSpecs, ExitCriteria
+    from libensemble.specs import SimSpecs, GenSpecs
 
 APOSMM supports a wide variety of external optimizers. The ``rc.aposmm_optimizers``
 statement above indicates to APOSMM which optimization method package to use,
@@ -156,9 +156,8 @@ Finally, we configure the simulation function, exit criteria, and run the workfl
     :linenos:
 
         workflow.sim_specs = SimSpecs(simulator=six_hump_camel_func, vocs=vocs)
-        workflow.exit_criteria = ExitCriteria(sim_max=2000)
 
-        H, _, _ = workflow.run()
+        H, _, _ = workflow.run(sim_max=2000)
 
         if workflow.is_manager:
             # We can map our variables back to an array for easy printing
diff --git a/docs/tutorials/gpcam_tutorial.rst b/docs/tutorials/gpcam_tutorial.rst
index 190697374..959ef22f2 100644
--- a/docs/tutorials/gpcam_tutorial.rst
+++ b/docs/tutorials/gpcam_tutorial.rst
@@ -210,7 +210,7 @@ If you wish to make your own functions based on the above, those can be imported
     from pprint import pprint
 
     from libensemble import Ensemble
-    from libensemble.specs import LibeSpecs, GenSpecs, SimSpecs, AllocSpecs, ExitCriteria
+    from libensemble.specs import LibeSpecs, GenSpecs, SimSpecs, AllocSpecs
 
     # If importing from libensemble
     from libensemble.gen_funcs.persistent_gpCAM import persistent_gpCAM
@@ -256,15 +256,12 @@ If you wish to make your own functions based on the above, those can be imported
         user={"async_return": False},  # False = batch returns
     )
 
-    exit_criteria = ExitCriteria(sim_max=num_batches * batch_size)
-
-    # Initialize and run the ensemble.
+    # Initialize the ensemble.
     ensemble = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         gen_specs=gen_specs,
         alloc_specs=alloc_specs,
-        exit_criteria=exit_criteria,
     )
 
 At the end of our calling script we run the ensemble.
@@ -275,7 +272,7 @@ At the end of our calling script we run the ensemble.
     cleanup()
     ensemble.persis_info = {}
 
-    H, persis_info, flag = ensemble.run()  # Start the ensemble. Blocks until completion.
+    H, persis_info, flag = ensemble.run(sim_max=num_batches * batch_size)  # Start the ensemble. Blocks until completion.
     ensemble.save_output("H_array", append_attrs=False)  # Save H (history of all evaluated points) to file
     pprint(H[["sim_id", "x", "f"]][:16])  # See first 16 results
 
@@ -293,7 +290,7 @@ To see how the accuracy of the surrogate model improves, we can use previously e
     cleanup()
     ensemble.persis_info = {}
 
-    H, persis_info, flag = ensemble.run()
+    H, persis_info, flag = ensemble.run(sim_max=num_batches * batch_size)
     print(persis_info)
 
 Viewing model progression
diff --git a/docs/tutorials/xopt_bayesian_gen.rst b/docs/tutorials/xopt_bayesian_gen.rst
index 9227ac8ce..bbdf756d9 100644
--- a/docs/tutorials/xopt_bayesian_gen.rst
+++ b/docs/tutorials/xopt_bayesian_gen.rst
@@ -25,7 +25,7 @@ Imports
 
     from libensemble import Ensemble
     from libensemble.alloc_funcs.start_only_persistent import only_persistent_gens as alloc_f
-    from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+    from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 Simulator Function
 ------------------
@@ -93,17 +93,15 @@ The simulator is a simple callable function that takes a dictionary of inputs an
     )
 
     alloc_specs = AllocSpecs(alloc_f=alloc_f)
-    exit_criteria = ExitCriteria(sim_max=12)
 
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         alloc_specs=alloc_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=12)
 
     if workflow.is_manager:
         print(f"Completed {len(H)} simulations")
@@ -158,10 +156,9 @@ Reset generator and change to libEnsemble-style simulator:
         sim_specs=sim_specs,
         alloc_specs=alloc_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=12)
 
     if workflow.is_manager:
         print(f"Completed {len(H)} simulations")
diff --git a/libensemble/ensemble.py b/libensemble/ensemble.py
index 24b47d72b..63365cbc2 100644
--- a/libensemble/ensemble.py
+++ b/libensemble/ensemble.py
@@ -1,7 +1,9 @@
 import logging
+import warnings
 
 import numpy.typing as npt
 
+from libensemble._deprecation import LibEnsembleDeprecationWarning
 from libensemble.executors import Executor
 from libensemble.libE import libE
 from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
@@ -19,6 +21,13 @@
 OVERWRITE_COMMS_WARN = "Cannot reset 'comms' if 'ensemble.libE_specs.comms' is already set."
 CHANGED_COMMS_WARN = "New 'comms' method detected following initialization of Ensemble. Exiting."
 
+EXIT_CRITERIA_DEPRECATION = (
+    "ExitCriteria as a standalone parameter is deprecated as of libEnsemble 2.0 "
+    "and will be removed in 2.1. Pass exit criteria directly to run() instead: "
+    "ensemble.run(sim_max=100) or ensemble.run(sim_max=100, wallclock_max=3600). "
+    "See https://libensemble.readthedocs.io/... for migration guidance."
+)
+
 CORRESPONDING_CLASSES = {
     "sim_specs": SimSpecs,
     "gen_specs": GenSpecs,
@@ -44,7 +53,7 @@ class Ensemble:
             from libensemble import Ensemble
             from libensemble.gen_classes.sampling import UniformSample
             from libensemble.sim_funcs.simple_sim import norm_eval
-            from libensemble.specs import ExitCriteria, GenSpecs, SimSpecs
+            from libensemble.specs import GenSpecs, SimSpecs
 
             sampling = Ensemble(parse_args=True)
 
@@ -66,10 +75,8 @@ class Ensemble:
                 batch_size=50,
             )
 
-            sampling.exit_criteria = ExitCriteria(sim_max=100)
-
             if __name__ == "__main__":
-                sampling.run()
+                sampling.run(sim_max=100)
                 sampling.save_output(__file__)
 
     Configure by:
@@ -159,7 +166,7 @@ def __init__(
         self,
         sim_specs: SimSpecs = SimSpecs(),
         gen_specs: GenSpecs = GenSpecs(),
-        exit_criteria: ExitCriteria = ExitCriteria(),
+        exit_criteria: ExitCriteria | None = None,
         libE_specs: LibeSpecs = LibeSpecs(),
         alloc_specs: AllocSpecs = AllocSpecs(),
         persis_info: dict = {},
@@ -169,7 +176,11 @@ def __init__(
     ):
         self.sim_specs = sim_specs
         self.gen_specs = gen_specs
-        self.exit_criteria = exit_criteria
+        self._exit_criteria = ExitCriteria()
+        if exit_criteria is not None:
+            if isinstance(exit_criteria, ExitCriteria):
+                warnings.warn(EXIT_CRITERIA_DEPRECATION, LibEnsembleDeprecationWarning, stacklevel=2)
+            self._exit_criteria = exit_criteria
         self._libE_specs: LibeSpecs = libE_specs
         self.alloc_specs = alloc_specs
         self.persis_info = persis_info
@@ -180,6 +191,7 @@ def __init__(
         self.is_manager = False
         self.parsed = False
         self._known_comms: str = ""
+        self._has_run_n_evals = False
 
         if parse_args:
             self._parse_args()
@@ -254,7 +266,9 @@ def ready(self) -> tuple[bool, list[str]]:
         ):
             issues.append(
                 "exit_criteria has no stop condition: set at least one of "
-                "'sim_max', 'gen_max', 'wallclock_max', or 'stop_val'."
+                "'sim_max', 'gen_max', 'wallclock_max', or 'stop_val' "
+                "either on an ExitCriteria object or directly via "
+                "ensemble.run(sim_max=..., gen_max=..., ...)."
             )
 
         # --- workers: must be determinable ---
@@ -308,13 +322,61 @@ def libE_specs(self, new_specs):
 
         self._libE_specs.__dict__.update(**new_specs)
 
+    @property
+    def exit_criteria(self) -> ExitCriteria:
+        return self._exit_criteria
+
+    @exit_criteria.setter
+    def exit_criteria(self, value: ExitCriteria | None):
+        if isinstance(value, ExitCriteria):
+            warnings.warn(EXIT_CRITERIA_DEPRECATION, LibEnsembleDeprecationWarning, stacklevel=2)
+        self._exit_criteria = value or ExitCriteria()
+
+    def reset(self) -> None:
+        """Reset the ensemble state to allow a fresh, independent run.
+
+        Clears the accumulated history (``H0``) and ``persis_info`` so that
+        the next :meth:`run` call starts from a clean slate — as if no
+        previous run had occurred.
+
+        Use this between two calls to :meth:`run` when you want **independent**
+        runs rather than the default history-chaining behaviour::
+
+            ens.run(sim_max=10)   # first independent run
+            ens.reset()           # clear accumulated history
+            ens.run(sim_max=20)   # second independent run, H0 is empty again
+        """
+        self.H0 = None
+        self.persis_info = {}
+
     def _refresh_executor(self):
         Executor.executor = self.executor or Executor.executor
 
-    def run(self) -> tuple[npt.NDArray, dict, int]:
+    def run(
+        self,
+        sim_max: int | None = None,
+        gen_max: int | None = None,
+        wallclock_max: float | None = None,
+        stop_val: tuple[str, float] | None = None,
+    ) -> tuple[npt.NDArray, dict, int]:
         """
         Initializes libEnsemble.
 
+        Parameters
+        ----------
+        sim_max: int, Optional
+            Maximum number of new simulation evaluations for this run.
+            Overrides ``exit_criteria.sim_max`` for this call only.
+        gen_max: int, Optional
+            Maximum number of new generator calls for this run.
+            Overrides ``exit_criteria.gen_max`` for this call only.
+        wallclock_max: float, Optional
+            Wallclock timeout in seconds for this run.
+            Overrides ``exit_criteria.wallclock_max`` for this call only.
+        stop_val: tuple[str, float], Optional
+            Stop criterion ``(field, value)`` for this run.
+            Overrides ``exit_criteria.stop_val`` for this call only.
+
         .. dropdown:: MPI/comms Notes
 
             Manager--worker intercommunications are parsed from the ``comms`` key of
@@ -325,6 +387,25 @@ def run(self) -> tuple[npt.NDArray, dict, int]:
             will initiate on a **duplicate** of that communicator.
             Otherwise, a duplicate of ``COMM_WORLD`` will be used.
 
+        .. dropdown:: Substeps / multi-step usage
+
+            Pass exit-criteria kwargs to run a subset of an ensemble at a time.
+            The ensemble history (``H0``) is automatically chained across calls::
+
+                sampling = Ensemble(...)
+                sampling.sim_specs = SimSpecs(...)
+                sampling.gen_specs = GenSpecs(...)
+
+                # Run in three substeps
+                sampling.run(sim_max=30)
+                # ... adjust generator hyperparameters ...
+                sampling.run(sim_max=30)
+                sampling.run(sim_max=40)
+
+            When ``sim_max`` is used (from kwargs or ``exit_criteria``),
+            ``libE_specs.final_gen_send`` and ``libE_specs.reuse_output_dir`` are
+            automatically set to ``True`` to support persistent generators across runs.
+
         Returns
         -------
 
@@ -355,16 +436,41 @@ def run(self) -> tuple[npt.NDArray, dict, int]:
             raise ValueError(CHANGED_COMMS_WARN)
 
         assert self._libE_specs is not None
+
+        # Merge kwargs into effective exit criteria for this run
+        run_kwargs = {
+            k: v
+            for k, v in {
+                "sim_max": sim_max,
+                "gen_max": gen_max,
+                "wallclock_max": wallclock_max,
+                "stop_val": stop_val,
+            }.items()
+            if v is not None
+        }
+        if run_kwargs:
+            effective_exit = self._exit_criteria.model_copy(update=run_kwargs)
+            self._has_run_n_evals = True
+        else:
+            effective_exit = self._exit_criteria
+
+        if sim_max is not None or getattr(self._exit_criteria, "sim_max", None) is not None:
+            self._libE_specs.final_gen_send = True
+            self._libE_specs.reuse_output_dir = True
+
         self.H, self.persis_info, self.flag = libE(
             self.sim_specs,
             self.gen_specs,
-            self.exit_criteria,
+            effective_exit,
             persis_info=self.persis_info,
             alloc_specs=self.alloc_specs,
             libE_specs=self._libE_specs,
             H0=self.H0,
         )
 
+        # Chain history for next call
+        self.H0 = self.H
+
         return self.H, self.persis_info, self.flag
 
     @property
diff --git a/libensemble/gen_classes/preloaded.py b/libensemble/gen_classes/preloaded.py
index d032e205e..02e5a9b38 100644
--- a/libensemble/gen_classes/preloaded.py
+++ b/libensemble/gen_classes/preloaded.py
@@ -9,7 +9,7 @@
     import numpy as np
     from libensemble import Ensemble
     from libensemble.gen_classes.preloaded import PreloadedSampleGenerator
-    from libensemble.specs import ExitCriteria, GenSpecs, SimSpecs
+    from libensemble.specs import GenSpecs, SimSpecs
 
     H0 = np.zeros(500, dtype=[("x", float, 8), ("sim_id", int)])
     H0["x"] = my_existing_points
@@ -18,8 +18,7 @@
     sampling = Ensemble(parse_args=True)
     sampling.gen_specs = GenSpecs(generator=PreloadedSampleGenerator(H0))
     sampling.sim_specs = SimSpecs(sim_f=my_sim, inputs=["x"], out=[("f", float)])
-    sampling.exit_criteria = ExitCriteria(sim_max=len(H0))
-    sampling.run()
+    sampling.run(sim_max=len(H0))
 
 This replaces the legacy ``give_pregenerated_work`` allocator pattern, which
 required a custom ``AllocSpecs`` and bypassed the generator entirely.  With
@@ -84,7 +83,7 @@ class PreloadedSampleGenerator(Generator):
         from libensemble import Ensemble
         from libensemble.gen_classes.preloaded import PreloadedSampleGenerator
         from libensemble.sim_funcs.borehole import borehole as sim_f, gen_borehole_input
-        from libensemble.specs import ExitCriteria, GenSpecs, SimSpecs
+        from libensemble.specs import GenSpecs, SimSpecs
 
         n_samp = 1000
         pts = np.zeros(n_samp, dtype=[("x", float, 8)])
@@ -93,8 +92,7 @@ class PreloadedSampleGenerator(Generator):
         sampling = Ensemble(parse_args=True)
         sampling.gen_specs = GenSpecs(generator=PreloadedSampleGenerator(pts))
         sampling.sim_specs = SimSpecs(sim_f=sim_f, inputs=["x"], out=[("f", float)])
-        sampling.exit_criteria = ExitCriteria(sim_max=n_samp)
-        sampling.run()
+        sampling.run(sim_max=n_samp)
     """
 
     def __init__(
diff --git a/libensemble/tests/functionality_tests/test_1d_sampling_no_comms_given.py b/libensemble/tests/functionality_tests/test_1d_sampling_no_comms_given.py
index 90dab7507..904224414 100644
--- a/libensemble/tests/functionality_tests/test_1d_sampling_no_comms_given.py
+++ b/libensemble/tests/functionality_tests/test_1d_sampling_no_comms_given.py
@@ -22,7 +22,7 @@
 
 # Import libEnsemble items for this test
 from libensemble.sim_funcs.simple_sim import norm_eval as sim_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 from libensemble.tools import check_npy_file_exists
 
 # Main block is necessary only when using local comms with spawn start method (default on macOS and Windows).
@@ -46,17 +46,14 @@
         },
     )
 
-    exit_criteria = ExitCriteria(gen_max=501)
-
     sampling = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
     sampling.alloc_specs = AllocSpecs(alloc_f=give_sim_work_first)
-    H, persis_info, flag = sampling.run()
+    H, persis_info, flag = sampling.run(gen_max=501)
 
     if sampling.is_manager:
         assert len(H) >= 501
diff --git a/libensemble/tests/functionality_tests/test_asktell_sampling_external_gen.py b/libensemble/tests/functionality_tests/test_asktell_sampling_external_gen.py
index 463fbbb0e..b50df3a23 100644
--- a/libensemble/tests/functionality_tests/test_asktell_sampling_external_gen.py
+++ b/libensemble/tests/functionality_tests/test_asktell_sampling_external_gen.py
@@ -22,7 +22,7 @@
 
 # from libensemble.gen_classes.external.sampling import UniformSampleArray
 from libensemble.gen_classes.external.sampling import UniformSample
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 # Import libEnsemble items for this test
 
@@ -75,17 +75,14 @@ def sim_f_scalar(In):
             vocs=vocs,
         )
 
-        exit_criteria = ExitCriteria(gen_max=201)
-
         ensemble = Ensemble(
             parse_args=True,
             sim_specs=sim_specs,
             gen_specs=gen_specs,
-            exit_criteria=exit_criteria,
             libE_specs=libE_specs,
         )
 
-        ensemble.run()
+        ensemble.run(gen_max=201)
 
         if ensemble.is_manager:
             print(ensemble.H[["sim_id", "x0", "x1", "f"]][:10])
diff --git a/libensemble/tests/functionality_tests/test_evaluate_existing_plus_gen.py b/libensemble/tests/functionality_tests/test_evaluate_existing_plus_gen.py
index 3e37bc86d..a3d7da360 100644
--- a/libensemble/tests/functionality_tests/test_evaluate_existing_plus_gen.py
+++ b/libensemble/tests/functionality_tests/test_evaluate_existing_plus_gen.py
@@ -21,7 +21,7 @@
 from libensemble.alloc_funcs.give_sim_work_first import give_sim_work_first
 from libensemble.gen_funcs.sampling import latin_hypercube_sample as gen_f
 from libensemble.sim_funcs.six_hump_camel import six_hump_camel as sim_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, SimSpecs
 
 
 def create_H0(gen_specs, H0_size):
@@ -55,14 +55,14 @@ def create_H0(gen_specs, H0_size):
         },
     }
     sampling.gen_specs = GenSpecs(**gen_specs)
-    sampling.exit_criteria = ExitCriteria(sim_max=100)
-    sampling.H0 = create_H0(gen_specs, 50)
+    H0 = create_H0(gen_specs, 50)
+    sampling.H0 = H0
     sampling.alloc_specs = AllocSpecs(alloc_f=give_sim_work_first)
-    sampling.run()
+    sampling.run(sim_max=100)
 
     if sampling.is_manager:
-        assert len(sampling.H) == 2 * len(sampling.H0)
-        assert np.array_equal(sampling.H0["x"][:50], sampling.H["x"][:50])
+        assert len(sampling.H) == 2 * len(H0)
+        assert np.array_equal(H0["x"][:50], sampling.H["x"][:50])
         assert np.all(sampling.H["sim_ended"])
         assert np.all(sampling.H["gen_worker"] == 0)
         print("\nlibEnsemble correctly appended to the initial sample via an additional gen.")
diff --git a/libensemble/tests/functionality_tests/test_executor_forces_tutorial.py b/libensemble/tests/functionality_tests/test_executor_forces_tutorial.py
index d6b368b93..d33316b2d 100644
--- a/libensemble/tests/functionality_tests/test_executor_forces_tutorial.py
+++ b/libensemble/tests/functionality_tests/test_executor_forces_tutorial.py
@@ -7,7 +7,7 @@
 from libensemble import Ensemble
 from libensemble.executors import MPIExecutor
 from libensemble.gen_funcs.persistent_sampling import persistent_uniform as gen_f
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":
     # Initialize MPI Executor
@@ -52,8 +52,5 @@
 
     # Starts one persistent generator. Simulated values are returned in batch.
 
-    # Instruct libEnsemble to exit after this many simulations
-    ensemble.exit_criteria = ExitCriteria(sim_max=8)
-
-    # Run ensemble
-    ensemble.run()
+    # Run ensemble; exit after this many simulations
+    ensemble.run(sim_max=8)
diff --git a/libensemble/tests/functionality_tests/test_executor_forces_tutorial_2.py b/libensemble/tests/functionality_tests/test_executor_forces_tutorial_2.py
index 2a6cda15b..77aca1d5d 100644
--- a/libensemble/tests/functionality_tests/test_executor_forces_tutorial_2.py
+++ b/libensemble/tests/functionality_tests/test_executor_forces_tutorial_2.py
@@ -7,7 +7,7 @@
 from libensemble import Ensemble, logger
 from libensemble.executors import MPIExecutor
 from libensemble.gen_funcs.persistent_sampling import persistent_uniform as gen_f
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 logger.set_level("DEBUG")
 
@@ -54,10 +54,7 @@
 
     # Starts one persistent generator. Simulated values are returned in batch.
 
-    # Instruct libEnsemble to exit after this many simulations
-    ensemble.exit_criteria = ExitCriteria(sim_max=8)
-
-    # Run ensemble
-    ensemble.run()
+    # Run ensemble; exit after this many simulations
+    ensemble.run(sim_max=8)
 
     ensemble.save_output(__file__)
diff --git a/libensemble/tests/functionality_tests/test_local_sine_tutorial.py b/libensemble/tests/functionality_tests/test_local_sine_tutorial.py
index 3c6fa0b32..4abffc5a2 100644
--- a/libensemble/tests/functionality_tests/test_local_sine_tutorial.py
+++ b/libensemble/tests/functionality_tests/test_local_sine_tutorial.py
@@ -4,7 +4,7 @@
 from sine_sim import sim_find_sine
 
 from libensemble import Ensemble
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":  # Python-quirk required on macOS and windows
     libE_specs = LibeSpecs(nworkers=4, comms="local")
@@ -25,10 +25,8 @@
         out=[("y", float)],  # sim_f output. "y" = sine("x")
     )  # sim_specs_end_tag
 
-    exit_criteria = ExitCriteria(sim_max=80)  # Stop libEnsemble after 80 simulations
-
-    ensemble = Ensemble(sim_specs, gen_specs, exit_criteria, libE_specs)
-    ensemble.run()  # start the ensemble. Blocks until completion.
+    ensemble = Ensemble(sim_specs, gen_specs, libE_specs=libE_specs)
+    ensemble.run(sim_max=80)  # start the ensemble. Blocks until completion.
 
     history = ensemble.H  # start visualizing our results
 
diff --git a/libensemble/tests/functionality_tests/test_local_sine_tutorial_2.py b/libensemble/tests/functionality_tests/test_local_sine_tutorial_2.py
index 286a0ecdc..8c794298c 100644
--- a/libensemble/tests/functionality_tests/test_local_sine_tutorial_2.py
+++ b/libensemble/tests/functionality_tests/test_local_sine_tutorial_2.py
@@ -4,7 +4,7 @@
 
 from libensemble import Ensemble
 from libensemble.alloc_funcs.give_sim_work_first import give_sim_work_first
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":
     libE_specs = LibeSpecs(nworkers=4, comms="local")
@@ -27,10 +27,8 @@
 
     alloc_specs = AllocSpecs(alloc_f=give_sim_work_first)
 
-    exit_criteria = ExitCriteria(gen_max=160)
-
-    ensemble = Ensemble(sim_specs, gen_specs, exit_criteria, libE_specs, alloc_specs)
-    ensemble.run()
+    ensemble = Ensemble(sim_specs, gen_specs, libE_specs=libE_specs, alloc_specs=alloc_specs)
+    ensemble.run(gen_max=160)
 
     if ensemble.flag != 0:
         print("Oh no! An error occurred!")
diff --git a/libensemble/tests/functionality_tests/test_local_sine_tutorial_3.py b/libensemble/tests/functionality_tests/test_local_sine_tutorial_3.py
index 988fe0e78..2b54d37c5 100644
--- a/libensemble/tests/functionality_tests/test_local_sine_tutorial_3.py
+++ b/libensemble/tests/functionality_tests/test_local_sine_tutorial_3.py
@@ -4,7 +4,7 @@
 
 from libensemble import Ensemble
 from libensemble.alloc_funcs.give_sim_work_first import give_sim_work_first
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, SimSpecs
 
 if __name__ == "__main__":  # Python-quirk required on macOS and windows
     # libE_specs = LibeSpecs(nworkers=4, comms="local")
@@ -25,14 +25,12 @@
         out=[("y", float)],  # sim_f output. "y" = sine("x")
     )  # sim_specs_end_tag
 
-    exit_criteria = ExitCriteria(sim_max=80)  # Stop libEnsemble after 80 simulations
-
     alloc_specs = AllocSpecs(alloc_f=give_sim_work_first)
 
     # replace libE_specs with parse_args=True. Detects MPI runtime
-    ensemble = Ensemble(sim_specs, gen_specs, exit_criteria, alloc_specs=alloc_specs, parse_args=True)
+    ensemble = Ensemble(sim_specs, gen_specs, alloc_specs=alloc_specs, parse_args=True)
 
-    ensemble.run()  # start the ensemble. Blocks until completion.
+    ensemble.run(sim_max=80)  # start the ensemble. Blocks until completion.
 
     if ensemble.is_manager:  # only True on rank 0
         history = ensemble.H  # start visualizing our results
diff --git a/libensemble/tests/functionality_tests/test_mpi_warning.py b/libensemble/tests/functionality_tests/test_mpi_warning.py
index f58620b90..7edaa1eae 100644
--- a/libensemble/tests/functionality_tests/test_mpi_warning.py
+++ b/libensemble/tests/functionality_tests/test_mpi_warning.py
@@ -22,7 +22,7 @@
 
 # Import libEnsemble items for this test
 from libensemble.sim_funcs.simple_sim import norm_eval as sim_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, SimSpecs
 
 # Main block is necessary only when using local comms with spawn start method (default on macOS and Windows).
 if __name__ == "__main__":
@@ -44,13 +44,11 @@
     )
     sampling.alloc_specs = AllocSpecs(alloc_f=give_sim_work_first)
 
-    sampling.exit_criteria = ExitCriteria(sim_max=100)
-
     if sampling.is_manager:
         if os.path.exists(log_file):
             os.remove(log_file)
 
-    sampling.run()
+    sampling.run(sim_max=100)
     if sampling.is_manager:
         print("len:", len(sampling.H))
         time.sleep(0.2)
diff --git a/libensemble/tests/regression_tests/test_1d_sampling.py b/libensemble/tests/regression_tests/test_1d_sampling.py
index 456b3ca60..3bbccdead 100644
--- a/libensemble/tests/regression_tests/test_1d_sampling.py
+++ b/libensemble/tests/regression_tests/test_1d_sampling.py
@@ -20,7 +20,7 @@
 
 # Import libEnsemble items for this test
 from libensemble.sim_funcs.simple_sim import norm_eval as sim_f
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":
     sampling = Ensemble(parse_args=True)
@@ -37,9 +37,7 @@
         },
     )
 
-    sampling.exit_criteria = ExitCriteria(sim_max=500)
-
-    sampling.run()
+    sampling.run(sim_max=500)
     if sampling.is_manager:
         assert len(sampling.H) >= 500
         print("\nlibEnsemble with random sampling has generated enough points")
diff --git a/libensemble/tests/regression_tests/test_2d_sampling.py b/libensemble/tests/regression_tests/test_2d_sampling.py
index c26a66201..d3c783d75 100644
--- a/libensemble/tests/regression_tests/test_2d_sampling.py
+++ b/libensemble/tests/regression_tests/test_2d_sampling.py
@@ -21,7 +21,7 @@
 
 # Import libEnsemble items for this test
 from libensemble.sim_funcs.simple_sim import norm_eval as sim_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 # Main block is necessary only when using local comms with spawn start method (default on macOS and Windows).
 if __name__ == "__main__":
@@ -40,9 +40,7 @@
 
     sampling.alloc_specs = AllocSpecs(alloc_f=give_sim_work_first)
 
-    sampling.exit_criteria = ExitCriteria(sim_max=200)
-
-    sampling.run()
+    sampling.run(sim_max=200)
     if sampling.is_manager:
         assert len(sampling.H) >= 200
         x = sampling.H["x"]
diff --git a/libensemble/tests/regression_tests/test_2d_sampling_vocs.py b/libensemble/tests/regression_tests/test_2d_sampling_vocs.py
index f535e1709..563a95162 100644
--- a/libensemble/tests/regression_tests/test_2d_sampling_vocs.py
+++ b/libensemble/tests/regression_tests/test_2d_sampling_vocs.py
@@ -17,7 +17,7 @@
 
 from libensemble import Ensemble
 from libensemble.gen_classes.sampling import LatinHypercubeSample
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 
 def sim_f(In, persis_info, sim_specs, _):
@@ -45,14 +45,12 @@ def sim_f(In, persis_info, sim_specs, _):
         batch_size=100,
     )
 
-    sampling.exit_criteria = ExitCriteria(sim_max=200)
-
-    sampling.run()
+    sampling.run(sim_max=200)
     if sampling.is_manager:
         assert len(sampling.H) >= 200
         x0 = sampling.H["x0"]
         x1 = sampling.H["x1"]
         f = sampling.H["f"]
-        assert np.all(np.isclose(f, np.sqrt(x0 ** 2 + x1 ** 2)))
+        assert np.all(np.isclose(f, np.sqrt(x0**2 + x1**2)))
         print("\nlibEnsemble has calculated the 2D vector norm of all points")
     sampling.save_output(__file__)
diff --git a/libensemble/tests/regression_tests/test_GPU_variable_resources.py b/libensemble/tests/regression_tests/test_GPU_variable_resources.py
index c8455b459..357184a2a 100644
--- a/libensemble/tests/regression_tests/test_GPU_variable_resources.py
+++ b/libensemble/tests/regression_tests/test_GPU_variable_resources.py
@@ -35,7 +35,7 @@
 # Import libEnsemble items for this test
 from libensemble.sim_funcs import six_hump_camel
 from libensemble.sim_funcs.var_resources import gpu_variable_resources_from_gen as sim_f
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 # logger.set_level("DEBUG")  # For testing the test
 
@@ -78,18 +78,15 @@
 
     # Run with random num_procs/num_gpus for each simulation
     gpu_test.persis_info = {}
-    gpu_test.exit_criteria = ExitCriteria(sim_max=10)
-
-    gpu_test.run()
+    gpu_test.run(sim_max=10)
     if gpu_test.is_manager:
         assert gpu_test.flag == 0
 
-    # Run with num_gpus based on x[0] for each simulation
+    # Run with num_gpus based on x[0] for each simulation (independent run)
     gpu_test.gen_specs.gen_f = gen_f2
     gpu_test.gen_specs.user["max_gpus"] = gpu_test.nworkers - 1
-    gpu_test.persis_info = {}
-    gpu_test.exit_criteria = ExitCriteria(sim_max=20)
-    gpu_test.run()
+    gpu_test.reset()
+    gpu_test.run(sim_max=20)
 
     if gpu_test.is_manager:
         assert gpu_test.flag == 0
diff --git a/libensemble/tests/regression_tests/test_GPU_variable_resources_multi_task.py b/libensemble/tests/regression_tests/test_GPU_variable_resources_multi_task.py
index 5564e7f96..38fb327f0 100644
--- a/libensemble/tests/regression_tests/test_GPU_variable_resources_multi_task.py
+++ b/libensemble/tests/regression_tests/test_GPU_variable_resources_multi_task.py
@@ -45,7 +45,7 @@
 # Import libEnsemble items for this test
 from libensemble.sim_funcs import six_hump_camel
 from libensemble.sim_funcs.var_resources import gpu_variable_resources_from_gen as sim_f
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 # logger.set_level("DEBUG")  # For testing the test
 
@@ -87,10 +87,8 @@
         },
     )
 
-    gpu_test.exit_criteria = ExitCriteria(sim_max=10, wallclock_max=300)
-
     if gpu_test.ready():
-        gpu_test.run()
+        gpu_test.run(sim_max=10, wallclock_max=300)
 
     if gpu_test.is_manager:
         assert gpu_test.flag == 0
diff --git a/libensemble/tests/regression_tests/test_asktell_aposmm_nlopt.py b/libensemble/tests/regression_tests/test_asktell_aposmm_nlopt.py
index 2a68d6e72..1427edcf0 100644
--- a/libensemble/tests/regression_tests/test_asktell_aposmm_nlopt.py
+++ b/libensemble/tests/regression_tests/test_asktell_aposmm_nlopt.py
@@ -30,7 +30,7 @@
 
 from libensemble import Ensemble
 from libensemble.gen_classes import APOSMM
-from libensemble.specs import ExitCriteria, GenSpecs, SimSpecs
+from libensemble.specs import GenSpecs, SimSpecs
 from libensemble.tests.regression_tests.support import six_hump_camel_minima as minima
 
 
@@ -90,10 +90,8 @@ def six_hump_camel_func(x):
     )
 
     workflow.sim_specs = SimSpecs(simulator=six_hump_camel_func, vocs=vocs)
-    workflow.exit_criteria = ExitCriteria(sim_max=3000, wallclock_max=600)
-
     # Perform the run
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=3000, wallclock_max=600)
 
     if workflow.is_manager:
         print("[Manager]:", H[np.where(H["local_min"])]["x"])
diff --git a/libensemble/tests/regression_tests/test_evaluate_existing_sample.py b/libensemble/tests/regression_tests/test_evaluate_existing_sample.py
index 8f1ee674c..0c3e69911 100644
--- a/libensemble/tests/regression_tests/test_evaluate_existing_sample.py
+++ b/libensemble/tests/regression_tests/test_evaluate_existing_sample.py
@@ -21,7 +21,7 @@
 from libensemble.alloc_funcs.give_pregenerated_work import give_pregenerated_sim_work as alloc_f
 from libensemble.sim_funcs.borehole import borehole as sim_f
 from libensemble.sim_funcs.borehole import gen_borehole_input
-from libensemble.specs import AllocSpecs, ExitCriteria, SimSpecs
+from libensemble.specs import AllocSpecs, SimSpecs
 
 # Main block is necessary only when using local comms with spawn start method (default on macOS and Windows).
 if __name__ == "__main__":
@@ -36,8 +36,7 @@
     sampling.H0 = H0
     sampling.sim_specs = SimSpecs(sim_f=sim_f, inputs=["x"], out=[("f", float)])
     sampling.alloc_specs = AllocSpecs(alloc_f=alloc_f)
-    sampling.exit_criteria = ExitCriteria(sim_max=len(H0))
-    sampling.run()
+    sampling.run(sim_max=len(H0))
 
     if sampling.is_manager:
         assert len(sampling.H) == len(H0)
diff --git a/libensemble/tests/regression_tests/test_evaluate_mixed_sample.py b/libensemble/tests/regression_tests/test_evaluate_mixed_sample.py
index 60e43fa57..f61689f4f 100644
--- a/libensemble/tests/regression_tests/test_evaluate_mixed_sample.py
+++ b/libensemble/tests/regression_tests/test_evaluate_mixed_sample.py
@@ -24,7 +24,7 @@
 # Import libEnsemble items for this test
 from libensemble.sim_funcs.borehole import borehole as sim_f
 from libensemble.sim_funcs.borehole import borehole_func, gen_borehole_input
-from libensemble.specs import AllocSpecs, ExitCriteria, SimSpecs
+from libensemble.specs import AllocSpecs, SimSpecs
 
 warnings.filterwarnings("ignore", category=DeprecationWarning)
 
@@ -47,8 +47,7 @@
     sampling.H0 = H0
     sampling.sim_specs = SimSpecs(sim_f=sim_f, inputs=["x"], out=[("f", float)])
     sampling.alloc_specs = AllocSpecs(alloc_f=alloc_f)
-    sampling.exit_criteria = ExitCriteria(sim_max=len(H0))
-    sampling.run()
+    sampling.run(sim_max=len(H0))
 
     if sampling.is_manager:
         assert len(sampling.H) == len(H0)
diff --git a/libensemble/tests/regression_tests/test_inverse_bayes_example.py b/libensemble/tests/regression_tests/test_inverse_bayes_example.py
index 72fa6eed0..23a1df9ad 100644
--- a/libensemble/tests/regression_tests/test_inverse_bayes_example.py
+++ b/libensemble/tests/regression_tests/test_inverse_bayes_example.py
@@ -24,7 +24,7 @@
 from libensemble.alloc_funcs.inverse_bayes_allocf import only_persistent_gens_for_inverse_bayes as alloc_f
 from libensemble.gen_funcs.persistent_inverse_bayes import persistent_updater_after_likelihood as gen_f
 from libensemble.sim_funcs.inverse_bayes import likelihood_calculator as sim_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, SimSpecs
 
 if __name__ == "__main__":
     # Parse args for test code
@@ -59,10 +59,9 @@
     bayes_test.persis_info = {}
     gen_user = bayes_test.gen_specs.user
     val = gen_user["subbatch_size"] * gen_user["num_subbatches"] * gen_user["num_batches"]
-    bayes_test.exit_criteria = ExitCriteria(sim_max=val, wallclock_max=300)
 
     # Perform the run
-    H, _, flag = bayes_test.run()
+    H, _, flag = bayes_test.run(sim_max=val, wallclock_max=300)
 
     if bayes_test.is_manager:
         assert flag == 0
diff --git a/libensemble/tests/regression_tests/test_optimas_ax_mf.py b/libensemble/tests/regression_tests/test_optimas_ax_mf.py
index fb5b75c32..62ce184db 100644
--- a/libensemble/tests/regression_tests/test_optimas_ax_mf.py
+++ b/libensemble/tests/regression_tests/test_optimas_ax_mf.py
@@ -23,7 +23,7 @@
 from optimas.generators import AxMultiFidelityGenerator
 
 from libensemble import Ensemble
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 
 def eval_func_mf(input_params):
@@ -61,16 +61,13 @@ def eval_func_mf(input_params):
         vocs=vocs,
     )
 
-    exit_criteria = ExitCriteria(sim_max=6)
-
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=6)
 
     # Perform the run
     if workflow.is_manager:
diff --git a/libensemble/tests/regression_tests/test_optimas_ax_multitask.py b/libensemble/tests/regression_tests/test_optimas_ax_multitask.py
index 08d97ed6b..cd5ca0615 100644
--- a/libensemble/tests/regression_tests/test_optimas_ax_multitask.py
+++ b/libensemble/tests/regression_tests/test_optimas_ax_multitask.py
@@ -31,7 +31,7 @@
 from optimas.generators import AxMultitaskGenerator
 
 from libensemble import Ensemble
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 
 def eval_func_multitask(input_params):
@@ -72,8 +72,6 @@ def eval_func_multitask(input_params):
         vocs=vocs,
     )
 
-    exit_criteria = ExitCriteria(sim_max=15)
-
     H0 = None  # or np.load("multitask_first_pass.npy")
     for run_num in range(2):
         print(f"\nRun number: {run_num}")
@@ -91,11 +89,10 @@ def eval_func_multitask(input_params):
             libE_specs=libE_specs,
             sim_specs=sim_specs,
             gen_specs=gen_specs,
-            exit_criteria=exit_criteria,
             H0=H0,
         )
 
-        H, _, _ = workflow.run()
+        H, _, _ = workflow.run(sim_max=15)
 
         if run_num == 0:
             H0 = H
diff --git a/libensemble/tests/regression_tests/test_optimas_ax_sf.py b/libensemble/tests/regression_tests/test_optimas_ax_sf.py
index b9fbbb34b..b91a18beb 100644
--- a/libensemble/tests/regression_tests/test_optimas_ax_sf.py
+++ b/libensemble/tests/regression_tests/test_optimas_ax_sf.py
@@ -23,7 +23,7 @@
 from optimas.generators import AxSingleFidelityGenerator
 
 from libensemble import Ensemble
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 
 def eval_func_sf(input_params):
@@ -63,16 +63,13 @@ def eval_func_sf(input_params):
         vocs=vocs,
     )
 
-    exit_criteria = ExitCriteria(sim_max=10)
-
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=10)
 
     # Perform the run
     if workflow.is_manager:
diff --git a/libensemble/tests/regression_tests/test_optimas_grid_sample.py b/libensemble/tests/regression_tests/test_optimas_grid_sample.py
index 5ec670aa9..78d9ec2ed 100644
--- a/libensemble/tests/regression_tests/test_optimas_grid_sample.py
+++ b/libensemble/tests/regression_tests/test_optimas_grid_sample.py
@@ -24,7 +24,7 @@
 from optimas.generators import GridSamplingGenerator
 
 from libensemble import Ensemble
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 
 def eval_func(input_params: dict):
@@ -72,16 +72,13 @@ def eval_func(input_params: dict):
         vocs=vocs,
     )
 
-    exit_criteria = ExitCriteria(sim_max=n_evals)
-
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=n_evals)
 
     # Perform the run
     if workflow.is_manager:
diff --git a/libensemble/tests/regression_tests/test_persistent_fd_param_finder.py b/libensemble/tests/regression_tests/test_persistent_fd_param_finder.py
index c0f2cff17..b0c7f4b6a 100644
--- a/libensemble/tests/regression_tests/test_persistent_fd_param_finder.py
+++ b/libensemble/tests/regression_tests/test_persistent_fd_param_finder.py
@@ -28,7 +28,7 @@
 # Import libEnsemble items for this test
 from libensemble.sim_funcs.noisy_vector_mapping import func_wrapper as sim_f
 from libensemble.sim_funcs.noisy_vector_mapping import noisy_function
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, SimSpecs
 
 if __name__ == "__main__":
     x0 = np.array([1.23, 4.56])  # point about which we are calculating finite difference parameters
@@ -58,16 +58,16 @@
             },
         ),
         alloc_specs=AllocSpecs(alloc_f=alloc_f),
-        exit_criteria=ExitCriteria(gen_max=1000),
     )
     fd_test.persis_info = {}
 
     shutil.copy("./scripts_used_by_reg_tests/ECnoise.m", "./")
 
-    H, persis_info, _ = fd_test.run()
+    gen_max = 1000
+    H, persis_info, _ = fd_test.run(gen_max=gen_max)
 
     if fd_test.is_manager:
-        assert len(H) < fd_test.exit_criteria.gen_max, "Problem didn't stop early, which should have been the case."
+        assert len(H) < gen_max, "Problem didn't stop early, which should have been the case."
         assert np.all(persis_info[0]["Fnoise"] > 0), "gen_f didn't find noise for all F_i components."
 
         fd_test.save_output(__file__)
diff --git a/libensemble/tests/regression_tests/test_persistent_surmise_calib.py b/libensemble/tests/regression_tests/test_persistent_surmise_calib.py
index 3820bfdec..b2f3b6fef 100644
--- a/libensemble/tests/regression_tests/test_persistent_surmise_calib.py
+++ b/libensemble/tests/regression_tests/test_persistent_surmise_calib.py
@@ -40,7 +40,7 @@
 # Import libEnsemble items for this test
 from libensemble.sim_funcs.surmise_test_function import borehole as sim_f
 from libensemble.sim_funcs.surmise_test_function import tstd2theta
-from libensemble.specs import ExitCriteria, GenSpecs, SimSpecs
+from libensemble.specs import GenSpecs, SimSpecs
 from libensemble.tools import parse_args
 
 
@@ -98,11 +98,10 @@ def run_surmise_calib():
             async_return=True,
             active_recv_gen=True,
         ),
-        exit_criteria=ExitCriteria(sim_max=max_evals),
     )
 
     # Perform the run
-    H, _, _ = test.run()
+    H, _, _ = test.run(sim_max=max_evals)
 
     if test.is_manager:
         print("Cancelled sims", H["sim_id"][H["cancel_requested"]])
diff --git a/libensemble/tests/regression_tests/test_proxystore_integration.py b/libensemble/tests/regression_tests/test_proxystore_integration.py
index 22e447286..50b29730e 100644
--- a/libensemble/tests/regression_tests/test_proxystore_integration.py
+++ b/libensemble/tests/regression_tests/test_proxystore_integration.py
@@ -24,7 +24,7 @@
 from libensemble import Ensemble
 from libensemble.alloc_funcs.give_pregenerated_work import give_pregenerated_sim_work as alloc_f
 from libensemble.sim_funcs.borehole import gen_borehole_input
-from libensemble.specs import AllocSpecs, ExitCriteria, SimSpecs
+from libensemble.specs import AllocSpecs, SimSpecs
 
 
 def insert_proxy(H0):
@@ -79,8 +79,7 @@ def one_d_example(x, persis_info, sim_specs, info):
     sampling.H0 = H0
     sampling.sim_specs = SimSpecs(sim_f=one_d_example, inputs=["x", "proxy"], outputs=[("f", float)])
     sampling.alloc_specs = AllocSpecs(alloc_f=alloc_f)
-    sampling.exit_criteria = ExitCriteria(sim_max=len(H0))
-    sampling.run()
+    sampling.run(sim_max=len(H0))
 
     if sampling.is_manager:
         assert len(sampling.H) == len(H0)
diff --git a/libensemble/tests/regression_tests/test_xopt_EI.py b/libensemble/tests/regression_tests/test_xopt_EI.py
index 7fb158b58..f45d58d26 100644
--- a/libensemble/tests/regression_tests/test_xopt_EI.py
+++ b/libensemble/tests/regression_tests/test_xopt_EI.py
@@ -23,7 +23,7 @@
 from xopt.generators.bayesian.expected_improvement import ExpectedImprovementGenerator
 
 from libensemble import Ensemble
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 
 # Adapted from Xopt/xopt/resources/testing.py
@@ -84,16 +84,13 @@ def xtest_sim(H, persis_info, sim_specs, _):
         vocs=vocs,
     )
 
-    exit_criteria = ExitCriteria(sim_max=20)
-
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=20)
 
     # Perform the run
     if workflow.is_manager:
diff --git a/libensemble/tests/regression_tests/test_xopt_EI_initial_sample.py b/libensemble/tests/regression_tests/test_xopt_EI_initial_sample.py
index d89de9449..8394308c8 100644
--- a/libensemble/tests/regression_tests/test_xopt_EI_initial_sample.py
+++ b/libensemble/tests/regression_tests/test_xopt_EI_initial_sample.py
@@ -25,7 +25,7 @@
 
 from libensemble import Ensemble
 from libensemble.alloc_funcs.start_only_persistent import only_persistent_gens as alloc_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 
 def xtest_sim(H, persis_info, sim_specs, _):
@@ -69,17 +69,15 @@ def xtest_sim(H, persis_info, sim_specs, _):
     )
 
     alloc_specs = AllocSpecs(alloc_f=alloc_f)
-    exit_criteria = ExitCriteria(sim_max=20)
 
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         alloc_specs=alloc_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=20)
 
     if workflow.is_manager:
         print(f"Completed {len(H)} simulations")
diff --git a/libensemble/tests/regression_tests/test_xopt_EI_initial_sample_instance.py b/libensemble/tests/regression_tests/test_xopt_EI_initial_sample_instance.py
index c7db6d363..08e02b6ec 100644
--- a/libensemble/tests/regression_tests/test_xopt_EI_initial_sample_instance.py
+++ b/libensemble/tests/regression_tests/test_xopt_EI_initial_sample_instance.py
@@ -27,7 +27,7 @@
 from libensemble import Ensemble
 from libensemble.alloc_funcs.start_only_persistent import only_persistent_gens as alloc_f
 from libensemble.gen_classes.sampling import LatinHypercubeSample
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 
 def xtest_sim(H, persis_info, sim_specs, _):
@@ -74,17 +74,15 @@ def xtest_sim(H, persis_info, sim_specs, _):
     )
 
     alloc_specs = AllocSpecs(alloc_f=alloc_f)
-    exit_criteria = ExitCriteria(sim_max=20)
 
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         alloc_specs=alloc_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=20)
 
     if workflow.is_manager:
         print(f"Completed {len(H)} simulations")
diff --git a/libensemble/tests/regression_tests/test_xopt_EI_xopt_sim.py b/libensemble/tests/regression_tests/test_xopt_EI_xopt_sim.py
index 13939169f..218ce5e90 100644
--- a/libensemble/tests/regression_tests/test_xopt_EI_xopt_sim.py
+++ b/libensemble/tests/regression_tests/test_xopt_EI_xopt_sim.py
@@ -23,7 +23,7 @@
 from xopt.generators.bayesian.expected_improvement import ExpectedImprovementGenerator
 
 from libensemble import Ensemble
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 
 # From Xopt/xopt/resources/testing.py
@@ -78,16 +78,13 @@ def xtest_callable(input_dict: dict, a=0) -> dict:
         vocs=vocs,
     )
 
-    exit_criteria = ExitCriteria(sim_max=20)
-
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=20)
 
     # Perform the run
     if workflow.is_manager:
diff --git a/libensemble/tests/regression_tests/test_xopt_nelder_mead.py b/libensemble/tests/regression_tests/test_xopt_nelder_mead.py
index 30d095207..288e45824 100644
--- a/libensemble/tests/regression_tests/test_xopt_nelder_mead.py
+++ b/libensemble/tests/regression_tests/test_xopt_nelder_mead.py
@@ -21,7 +21,7 @@
 from xopt.generators.sequential.neldermead import NelderMeadGenerator
 
 from libensemble import Ensemble
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 
 def rosenbrock_callable(input_dict: dict) -> dict:
@@ -66,16 +66,13 @@ def rosenbrock_callable(input_dict: dict) -> dict:
         vocs=vocs,
     )
 
-    exit_criteria = ExitCriteria(sim_max=30)
-
     workflow = Ensemble(
         libE_specs=libE_specs,
         sim_specs=sim_specs,
         gen_specs=gen_specs,
-        exit_criteria=exit_criteria,
     )
 
-    H, _, _ = workflow.run()
+    H, _, _ = workflow.run(sim_max=30)
 
     # Perform the run
     if workflow.is_manager:
diff --git a/libensemble/tests/scaling_tests/forces/forces_gpu/run_libe_forces.py b/libensemble/tests/scaling_tests/forces/forces_gpu/run_libe_forces.py
index 7b45ebd57..4b4513ea9 100644
--- a/libensemble/tests/scaling_tests/forces/forces_gpu/run_libe_forces.py
+++ b/libensemble/tests/scaling_tests/forces/forces_gpu/run_libe_forces.py
@@ -26,7 +26,7 @@
 from libensemble.alloc_funcs.start_only_persistent import only_persistent_gens as alloc_f
 from libensemble.executors import MPIExecutor
 from libensemble.gen_funcs.persistent_sampling import persistent_uniform as gen_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":
     # Initialize MPI Executor
@@ -75,15 +75,13 @@
         },
     )
 
-    # Instruct libEnsemble to exit after this many simulations
-    ensemble.exit_criteria = ExitCriteria(sim_max=8)
-
-    # Run ensemble
-    ensemble.run()
+    # Run ensemble; exit after this many simulations
+    sim_max = 8
+    ensemble.run(sim_max=sim_max)
 
     if ensemble.is_manager:
         # Note, this will change if changing sim_max, nworkers, lb, ub, etc.
-        if ensemble.exit_criteria.sim_max == 8:
+        if sim_max == 8:
             chksum = np.sum(ensemble.H["energy"])
             assert np.isclose(chksum, 96288744.35136001), f"energy check sum is {chksum}"
             print("Checksum passed")
diff --git a/libensemble/tests/scaling_tests/forces/forces_gpu_var_resources/run_libe_forces.py b/libensemble/tests/scaling_tests/forces/forces_gpu_var_resources/run_libe_forces.py
index 09a43e175..1f0ad675e 100644
--- a/libensemble/tests/scaling_tests/forces/forces_gpu_var_resources/run_libe_forces.py
+++ b/libensemble/tests/scaling_tests/forces/forces_gpu_var_resources/run_libe_forces.py
@@ -29,7 +29,7 @@
 from libensemble.alloc_funcs.start_only_persistent import only_persistent_gens as alloc_f
 from libensemble.executors import MPIExecutor
 from libensemble.gen_funcs.persistent_sampling_var_resources import uniform_sample_with_var_gpus as gen_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":
     # Initialize MPI Executor
@@ -83,15 +83,13 @@
         },
     )
 
-    # Instruct libEnsemble to exit after this many simulations.
-    ensemble.exit_criteria = ExitCriteria(sim_max=8)
-
-    # Run ensemble
-    ensemble.run()
+    # Run ensemble; exit after this many simulations
+    sim_max = 8
+    ensemble.run(sim_max=sim_max)
 
     if ensemble.is_manager:
         # Note, this will change if changing sim_max, nworkers, lb, ub, etc.
-        if ensemble.exit_criteria.sim_max == 8:
+        if sim_max == 8:
             chksum = np.sum(ensemble.H["energy"])
             assert np.isclose(chksum, 96288744.35136001), f"energy check sum is {chksum}"
             print("Checksum passed")
diff --git a/libensemble/tests/scaling_tests/forces/forces_multi_app/run_libe_forces.py b/libensemble/tests/scaling_tests/forces/forces_multi_app/run_libe_forces.py
index e5faeb9b4..b71c8ce50 100644
--- a/libensemble/tests/scaling_tests/forces/forces_multi_app/run_libe_forces.py
+++ b/libensemble/tests/scaling_tests/forces/forces_multi_app/run_libe_forces.py
@@ -33,7 +33,7 @@
 from libensemble.alloc_funcs.start_only_persistent import only_persistent_gens as alloc_f
 from libensemble.executors import MPIExecutor
 from libensemble.gen_funcs.persistent_sampling_var_resources import uniform_sample_diff_simulations as gen_f
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":
     # Initialize MPI Executor instance
@@ -95,11 +95,9 @@
         },
     )
 
-    # Instruct libEnsemble to exit after this many simulations.
-    ensemble.exit_criteria = ExitCriteria(sim_max=nsim_workers * 2)
-
-    # Run ensemble
-    ensemble.run()
+    # Run ensemble; exit after this many simulations
+    sim_max = nsim_workers * 2
+    ensemble.run(sim_max=sim_max)
 
     if ensemble.is_manager:
         # Note, this will change if changing sim_max, nworkers, lb, ub, etc.
@@ -107,7 +105,7 @@
         print(f"Final energy checksum: {chksum}")
 
         exp_chksums = {16: -21935405.696289998, 32: -26563930.6356}
-        exp_chksum = exp_chksums.get(ensemble.exit_criteria.sim_max)
+        exp_chksum = exp_chksums.get(sim_max)
 
         if exp_chksum is not None:
             assert np.isclose(chksum, exp_chksum), f"energy check sum is {chksum}"
diff --git a/libensemble/tests/scaling_tests/forces/forces_simple/run_libe_forces.py b/libensemble/tests/scaling_tests/forces/forces_simple/run_libe_forces.py
index a337a09e4..8c99fe2dd 100644
--- a/libensemble/tests/scaling_tests/forces/forces_simple/run_libe_forces.py
+++ b/libensemble/tests/scaling_tests/forces/forces_simple/run_libe_forces.py
@@ -9,7 +9,7 @@
 from libensemble import Ensemble
 from libensemble.executors import MPIExecutor
 from libensemble.gen_funcs.persistent_sampling import persistent_uniform as gen_f
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":
     # Initialize MPI Executor
@@ -54,11 +54,8 @@
 
     # Starts one persistent generator. Simulated values are returned in batch.
 
-    # Instruct libEnsemble to exit after this many simulations
-    ensemble.exit_criteria = ExitCriteria(sim_max=8)
-
-    # Run ensemble
-    ensemble.run()
+    # Run ensemble; exit after this many simulations
+    ensemble.run(sim_max=8)
 
     if ensemble.is_manager:
         # Note, this will change if changing sim_max, nworkers, lb, ub, etc.
diff --git a/libensemble/tests/scaling_tests/forces/forces_simple_with_input_file/run_libe_forces.py b/libensemble/tests/scaling_tests/forces/forces_simple_with_input_file/run_libe_forces.py
index 9c066ec93..189443b9b 100644
--- a/libensemble/tests/scaling_tests/forces/forces_simple_with_input_file/run_libe_forces.py
+++ b/libensemble/tests/scaling_tests/forces/forces_simple_with_input_file/run_libe_forces.py
@@ -9,7 +9,7 @@
 from libensemble import Ensemble
 from libensemble.executors import MPIExecutor
 from libensemble.gen_funcs.persistent_sampling import persistent_uniform as gen_f
-from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
 if __name__ == "__main__":
     # Initialize MPI Executor
@@ -58,11 +58,8 @@
 
     # Starts one persistent generator. Simulated values are returned in batch.
 
-    # Instruct libEnsemble to exit after this many simulations
-    ensemble.exit_criteria = ExitCriteria(sim_max=8)
-
-    # Run ensemble
-    ensemble.run()
+    # Run ensemble; exit after this many simulations
+    ensemble.run(sim_max=8)
 
     if ensemble.is_manager:
         # Note, this will change if changing sim_max, nworkers, lb, ub, etc.
diff --git a/libensemble/tests/scaling_tests/forces/forces_simple_xopt/run_libe_forces.py b/libensemble/tests/scaling_tests/forces/forces_simple_xopt/run_libe_forces.py
index 2d23c83a8..c3e5024f7 100644
--- a/libensemble/tests/scaling_tests/forces/forces_simple_xopt/run_libe_forces.py
+++ b/libensemble/tests/scaling_tests/forces/forces_simple_xopt/run_libe_forces.py
@@ -10,7 +10,7 @@
 from libensemble import Ensemble
 from libensemble.alloc_funcs.start_only_persistent import only_persistent_gens as alloc_f
 from libensemble.executors import MPIExecutor
-from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
 # from forces_simf import run_forces_dict  # gest-api/xopt style simulator.
 
@@ -64,11 +64,8 @@
         },
     )
 
-    # Instruct libEnsemble to exit after this many simulations
-    ensemble.exit_criteria = ExitCriteria(sim_max=8)
-
-    # Run ensemble
-    ensemble.run()
+    # Run ensemble; exit after this many simulations
+    ensemble.run(sim_max=8)
 
     if ensemble.is_manager:
         # Note, this will change if changing sim_max, nworkers, lb, ub, etc.
diff --git a/libensemble/tests/unit_tests/test_ensemble.py b/libensemble/tests/unit_tests/test_ensemble.py
index 0e5de3223..9de46c2f7 100644
--- a/libensemble/tests/unit_tests/test_ensemble.py
+++ b/libensemble/tests/unit_tests/test_ensemble.py
@@ -42,7 +42,7 @@ def test_full_workflow():
     from libensemble.ensemble import Ensemble
     from libensemble.gen_funcs.sampling import latin_hypercube_sample
     from libensemble.sim_funcs.simple_sim import norm_eval
-    from libensemble.specs import AllocSpecs, ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+    from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
 
     LS = LibeSpecs(comms="local", nworkers=4)
 
@@ -60,11 +60,10 @@ def test_full_workflow():
                 "ub": np.array([3]),
             },
         ),
-        exit_criteria=ExitCriteria(gen_max=101),
         alloc_specs=AllocSpecs(alloc_f=give_sim_work_first),
     )
 
-    ens.run()
+    ens.run(gen_max=101)
     if ens.is_manager:
         assert len(ens.H) >= 101
 
@@ -72,7 +71,7 @@ def test_full_workflow():
     ens.libE_specs.dry_run = True
     flag = 1
     try:
-        ens.run()
+        ens.run(gen_max=101)
     except SystemExit:
         flag = 0
     assert not flag, "Ensemble didn't exit after specifying dry_run"
@@ -85,7 +84,7 @@ def test_flakey_workflow():
     from libensemble.ensemble import Ensemble
     from libensemble.gen_funcs.sampling import latin_hypercube_sample
     from libensemble.sim_funcs.simple_sim import norm_eval
-    from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+    from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
     LS = LibeSpecs(comms="local", nworkers=4)
 
@@ -102,10 +101,9 @@ def test_flakey_workflow():
                     "ub": np.array([3]),
                 },
             ),
-            exit_criteria=ExitCriteria(gen_max=101),
         )
         ens.sim_specs.inputs = (["x"],)  # note trailing comma
-        ens.run()
+        ens.run(gen_max=101)
     except ValidationError:
         flag = 0
 
@@ -185,13 +183,13 @@ def test_local_comms_without_nworkers():
 def test_ready_missing_sim_callable():
     """ready() should flag a missing sim callable."""
     from libensemble.ensemble import Ensemble
-    from libensemble.specs import ExitCriteria, LibeSpecs, SimSpecs
+    from libensemble.specs import LibeSpecs, SimSpecs
 
     e = Ensemble(
         libE_specs=LibeSpecs(comms="local", nworkers=4),
         sim_specs=SimSpecs(),  # no sim_f or simulator
-        exit_criteria=ExitCriteria(sim_max=10),
     )
+    e._exit_criteria.sim_max = 10  # set directly to avoid deprecation warning
     ok, issues = e.ready()
     assert not ok, "Should not be ready without a sim callable"
     assert any("sim_f" in msg for msg in issues), f"Expected sim_f mention in issues: {issues}"
@@ -201,12 +199,12 @@ def test_ready_missing_exit_criteria():
     """ready() should flag an exit_criteria with no stop condition."""
     from libensemble.ensemble import Ensemble
     from libensemble.sim_funcs.simple_sim import norm_eval
-    from libensemble.specs import ExitCriteria, LibeSpecs, SimSpecs
+    from libensemble.specs import LibeSpecs, SimSpecs
 
     e = Ensemble(
         libE_specs=LibeSpecs(comms="local", nworkers=4),
         sim_specs=SimSpecs(sim_f=norm_eval),
-        exit_criteria=ExitCriteria(),  # nothing set
+        # no exit criteria set — _exit_criteria defaults to ExitCriteria() with nothing set
     )
     ok, issues = e.ready()
     assert not ok, "Should not be ready with no exit condition"
@@ -217,15 +215,15 @@ def test_ready_missing_nworkers_local():
     """ready() should flag local comms without nworkers."""
     from libensemble.ensemble import Ensemble
     from libensemble.sim_funcs.simple_sim import norm_eval
-    from libensemble.specs import ExitCriteria, LibeSpecs, SimSpecs
+    from libensemble.specs import LibeSpecs, SimSpecs
 
     # Bypass the constructor ValueError by using mpi comms first,
     # then patch to local after construction.
     e = Ensemble(
         libE_specs=LibeSpecs(comms="mpi"),
         sim_specs=SimSpecs(sim_f=norm_eval),
-        exit_criteria=ExitCriteria(sim_max=10),
     )
+    e._exit_criteria.sim_max = 10  # set directly to avoid deprecation warning
     # Manually force comms=local and nworkers=0 on the internal specs object
     e._libE_specs.comms = "local"
     e._nworkers = 0
@@ -240,14 +238,14 @@ def test_ready_field_mismatch():
     """ready() should flag when sim_specs.inputs requests fields not in gen_specs.outputs."""
     from libensemble.ensemble import Ensemble
     from libensemble.sim_funcs.simple_sim import norm_eval
-    from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+    from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
     e = Ensemble(
         libE_specs=LibeSpecs(comms="local", nworkers=4),
         sim_specs=SimSpecs(sim_f=norm_eval, inputs=["x", "z"]),
         gen_specs=GenSpecs(outputs=[("x", float, (1,))]),  # missing "z"
-        exit_criteria=ExitCriteria(sim_max=10),
     )
+    e._exit_criteria.sim_max = 10  # set directly to avoid deprecation warning
     ok, issues = e.ready()
     assert not ok, "Should not be ready with mismatched gen/sim fields"
     assert any("z" in msg for msg in issues), f"Expected missing field 'z' in issues: {issues}"
@@ -257,19 +255,188 @@ def test_ready_happy_path():
     """ready() should return (True, []) for a fully configured ensemble."""
     from libensemble.ensemble import Ensemble
     from libensemble.sim_funcs.simple_sim import norm_eval
-    from libensemble.specs import ExitCriteria, GenSpecs, LibeSpecs, SimSpecs
+    from libensemble.specs import GenSpecs, LibeSpecs, SimSpecs
 
     e = Ensemble(
         libE_specs=LibeSpecs(comms="local", nworkers=4),
         sim_specs=SimSpecs(sim_f=norm_eval, inputs=["x"], outputs=[("f", float)]),
         gen_specs=GenSpecs(outputs=[("x", float, (1,))]),
-        exit_criteria=ExitCriteria(sim_max=10),
     )
+    e._exit_criteria.sim_max = 10  # set directly to avoid deprecation warning
     ok, issues = e.ready()
     assert ok, f"Should be ready but got issues: {issues}"
     assert issues == [], f"Issues should be empty but got: {issues}"
 
 
+# --- run() kwargs / substep tests ---
+
+
+def test_run_sim_max_kwarg():
+    """run(sim_max=10) should evaluate exactly 10 simulations."""
+    from libensemble.alloc_funcs.give_sim_work_first import give_sim_work_first
+    from libensemble.ensemble import Ensemble
+    from libensemble.gen_funcs.sampling import latin_hypercube_sample
+    from libensemble.sim_funcs.simple_sim import norm_eval
+    from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
+
+    ens = Ensemble(
+        libE_specs=LibeSpecs(comms="local", nworkers=4),
+        sim_specs=SimSpecs(sim_f=norm_eval, inputs=["x"], outputs=[("f", float)]),
+        gen_specs=GenSpecs(
+            gen_f=latin_hypercube_sample,
+            outputs=[("x", float, (1,))],
+            persis_in=["f"],
+            batch_size=5,
+            user={"lb": np.array([-3]), "ub": np.array([3])},
+        ),
+        alloc_specs=AllocSpecs(alloc_f=give_sim_work_first),
+    )
+    ens.run(sim_max=10)
+    if ens.is_manager:
+        sim_count = int(np.sum(ens.H["sim_ended"]))
+        assert sim_count == 10, f"Expected 10 sims but got {sim_count}"
+
+
+def test_run_chaining():
+    """Two run(sim_max=N) calls should chain H0, doubling total."""
+    from libensemble.alloc_funcs.give_sim_work_first import give_sim_work_first
+    from libensemble.ensemble import Ensemble
+    from libensemble.gen_funcs.sampling import latin_hypercube_sample
+    from libensemble.sim_funcs.simple_sim import norm_eval
+    from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
+
+    ens = Ensemble(
+        libE_specs=LibeSpecs(comms="local", nworkers=4),
+        sim_specs=SimSpecs(sim_f=norm_eval, inputs=["x"], outputs=[("f", float)]),
+        gen_specs=GenSpecs(
+            gen_f=latin_hypercube_sample,
+            outputs=[("x", float, (1,))],
+            persis_in=["f"],
+            batch_size=5,
+            user={"lb": np.array([-3]), "ub": np.array([3])},
+        ),
+        alloc_specs=AllocSpecs(alloc_f=give_sim_work_first),
+    )
+    ens.run(sim_max=10)
+    h1_ended = int(np.sum(ens.H["sim_ended"])) if ens.is_manager else 0
+    ens.run(sim_max=10)
+    if ens.is_manager:
+        total_ended = int(np.sum(ens.H["sim_ended"]))
+        assert total_ended == h1_ended + 10, f"Expected {h1_ended + 10} sims ended but got {total_ended}"
+        assert ens.H0 is ens.H, "H0 should reference the latest H"
+
+
+def test_run_sim_max_merge():
+    """run() kwargs should merge with existing exit_criteria, not replace."""
+    from libensemble.alloc_funcs.give_sim_work_first import give_sim_work_first
+    from libensemble.ensemble import Ensemble
+    from libensemble.gen_funcs.sampling import latin_hypercube_sample
+    from libensemble.sim_funcs.simple_sim import norm_eval
+    from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
+
+    # Must have full sim/gen specs so run() actually works
+    ens = Ensemble(
+        libE_specs=LibeSpecs(comms="local", nworkers=4),
+        sim_specs=SimSpecs(sim_f=norm_eval, inputs=["x"], outputs=[("f", float)]),
+        gen_specs=GenSpecs(
+            gen_f=latin_hypercube_sample,
+            outputs=[("x", float, (1,))],
+            persis_in=["f"],
+            batch_size=5,
+            user={"lb": np.array([-3]), "ub": np.array([3])},
+        ),
+        alloc_specs=AllocSpecs(alloc_f=give_sim_work_first),
+    )
+    ens._exit_criteria.sim_max = 100  # set directly to avoid deprecation warning
+    ens.run(sim_max=10)
+    # stored exit_criteria should still have sim_max=100
+    assert ens.exit_criteria.sim_max == 100, f"Expected sim_max=100 but got {ens.exit_criteria.sim_max}"
+
+
+def test_exit_criteria_deprecation_init():
+    """Passing ExitCriteria to Ensemble() should emit a deprecation warning."""
+    import warnings
+
+    from libensemble._deprecation import LibEnsembleDeprecationWarning
+    from libensemble.ensemble import Ensemble
+    from libensemble.specs import ExitCriteria
+
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        Ensemble(exit_criteria=ExitCriteria(sim_max=10))
+    deprecations = [x for x in w if issubclass(x.category, LibEnsembleDeprecationWarning)]
+    assert len(deprecations) >= 1, "Expected at least one LibEnsembleDeprecationWarning"
+
+
+def test_exit_criteria_deprecation_setter():
+    """Setting ensemble.exit_criteria = ExitCriteria(...) should emit a deprecation warning."""
+    import warnings
+
+    from libensemble._deprecation import LibEnsembleDeprecationWarning
+    from libensemble.ensemble import Ensemble
+    from libensemble.specs import ExitCriteria, LibeSpecs
+
+    ens = Ensemble(libE_specs=LibeSpecs(comms="local", nworkers=4))
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        ens.exit_criteria = ExitCriteria(sim_max=10)
+    deprecations = [x for x in w if issubclass(x.category, LibEnsembleDeprecationWarning)]
+    assert len(deprecations) >= 1, "Expected at least one LibEnsembleDeprecationWarning"
+
+
+def test_run_auto_settings():
+    """run(sim_max=...) should auto-set final_gen_send and reuse_output_dir."""
+    from libensemble.alloc_funcs.give_sim_work_first import give_sim_work_first
+    from libensemble.ensemble import Ensemble
+    from libensemble.gen_funcs.sampling import latin_hypercube_sample
+    from libensemble.sim_funcs.simple_sim import norm_eval
+    from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
+
+    ens = Ensemble(
+        libE_specs=LibeSpecs(comms="local", nworkers=4),
+        sim_specs=SimSpecs(sim_f=norm_eval, inputs=["x"], outputs=[("f", float)]),
+        gen_specs=GenSpecs(
+            gen_f=latin_hypercube_sample,
+            outputs=[("x", float, (1,))],
+            persis_in=["f"],
+            batch_size=5,
+            user={"lb": np.array([-3]), "ub": np.array([3])},
+        ),
+        alloc_specs=AllocSpecs(alloc_f=give_sim_work_first),
+    )
+    ens.run(sim_max=10)
+    assert ens.libE_specs.final_gen_send is True
+    assert ens.libE_specs.reuse_output_dir is True
+
+
+def test_h0_chaining_plain_run():
+    """H0 should be updated to H after a plain run() call."""
+    from libensemble.alloc_funcs.give_sim_work_first import give_sim_work_first
+    from libensemble.ensemble import Ensemble
+    from libensemble.gen_funcs.sampling import latin_hypercube_sample
+    from libensemble.sim_funcs.simple_sim import norm_eval
+    from libensemble.specs import AllocSpecs, GenSpecs, LibeSpecs, SimSpecs
+
+    ens = Ensemble(
+        libE_specs=LibeSpecs(comms="local", nworkers=4),
+        sim_specs=SimSpecs(sim_f=norm_eval, inputs=["x"], outputs=[("f", float)]),
+        gen_specs=GenSpecs(
+            gen_f=latin_hypercube_sample,
+            outputs=[("x", float, (1,))],
+            persis_in=["f"],
+            batch_size=5,
+            user={"lb": np.array([-3]), "ub": np.array([3])},
+        ),
+        alloc_specs=AllocSpecs(alloc_f=give_sim_work_first),
+    )
+    assert ens.H0 is None, "H0 should be None before first run"
+    ens.run(sim_max=5)
+    if ens.is_manager:
+        assert ens.H0 is not None, "H0 should be set after run"
+        sim_count = int(np.sum(ens.H0["sim_ended"]))
+        assert sim_count == 5, f"Expected H0 sim_ended count 5 but got {sim_count}"
+
+
 if __name__ == "__main__":
     test_ensemble_init()
     test_ensemble_parse_args_false()
@@ -283,3 +450,10 @@ def test_ready_happy_path():
     test_ready_missing_nworkers_local()
     test_ready_field_mismatch()
     test_ready_happy_path()
+    test_run_sim_max_kwarg()
+    test_run_chaining()
+    test_run_sim_max_merge()
+    test_exit_criteria_deprecation_init()
+    test_exit_criteria_deprecation_setter()
+    test_run_auto_settings()
+    test_h0_chaining_plain_run()