diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 116384561..262183abd 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -101,10 +101,11 @@ jobs:
         qcore --accept-license
 
     # note: psi4 on c-f pins to a single qcel and qcng, so this may be handy for solve-and-replace
-    #- name: Special Config - QCElemental Dep
+    - name: Special Config - QCElemental Dep
     #  if: (matrix.cfg.label == 'ADCC')
-    #  run: |
-    #    conda remove qcelemental --force
+      run: |
+        conda remove qcelemental --force
+        python -m pip install git+https://github.com/Lnaden/QCElemental.git@Pydanticv2Overhaul --no-deps
     #    python -m pip install qcelemental>=0.26.0 --no-deps
 
       # note: conda remove --force, not mamba remove --force b/c https://github.com/mamba-org/mamba/issues/412
diff --git a/devtools/conda-envs/adcc.yaml b/devtools/conda-envs/adcc.yaml
index cb10306fa..3f6205979 100644
--- a/devtools/conda-envs/adcc.yaml
+++ b/devtools/conda-envs/adcc.yaml
@@ -13,7 +13,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.24.0
-  - pydantic=1
+  - pydantic>=2.1
+  - pydantic-settings
   - msgpack-python
 
     # Testing
diff --git a/devtools/conda-envs/base.yaml b/devtools/conda-envs/base.yaml
index 2a74047f9..38bcea49e 100644
--- a/devtools/conda-envs/base.yaml
+++ b/devtools/conda-envs/base.yaml
@@ -8,7 +8,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.12.0
-  - pydantic>=1.0.0
+  - pydantic>=2.1
+  - pydantic-settings
 
     # Testing
   - pytest
diff --git a/devtools/conda-envs/docs-cf.yaml b/devtools/conda-envs/docs-cf.yaml
index 19b37fa32..2c396e2da 100644
--- a/devtools/conda-envs/docs-cf.yaml
+++ b/devtools/conda-envs/docs-cf.yaml
@@ -5,7 +5,8 @@ channels:
 dependencies:
   - python
   - networkx
-  - pydantic=1
+  - pydantic>=2.1
+  - pydantic-settings
   - numpy
   - pint
 
diff --git a/devtools/conda-envs/mrchem.yaml b/devtools/conda-envs/mrchem.yaml
index d0d0b752b..4319ca151 100644
--- a/devtools/conda-envs/mrchem.yaml
+++ b/devtools/conda-envs/mrchem.yaml
@@ -13,7 +13,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental>=0.24
-  - pydantic 
+  - pydantic>=2.1
+  - pydantic-settings
 
     # Testing
   - pytest
diff --git a/devtools/conda-envs/nwchem.yaml b/devtools/conda-envs/nwchem.yaml
index e86623e79..294416546 100644
--- a/devtools/conda-envs/nwchem.yaml
+++ b/devtools/conda-envs/nwchem.yaml
@@ -8,7 +8,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.24.0
-  - pydantic>=1.0.0
+  - pydantic>=2.1
+  - pydantic-settings
   - networkx>=2.4.0
 
     # Testing
diff --git a/devtools/conda-envs/openmm.yaml b/devtools/conda-envs/openmm.yaml
index ddd49e3b4..0c02ef1ff 100644
--- a/devtools/conda-envs/openmm.yaml
+++ b/devtools/conda-envs/openmm.yaml
@@ -16,7 +16,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.11.1
-  - pydantic >=1.8.2
+  - pydantic>=2.1
+  - pydantic-settings
   - pint <0.22
 
     # Testing
diff --git a/devtools/conda-envs/opt-disp.yaml b/devtools/conda-envs/opt-disp.yaml
index 7e1b8641a..2bf981819 100644
--- a/devtools/conda-envs/opt-disp.yaml
+++ b/devtools/conda-envs/opt-disp.yaml
@@ -25,7 +25,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.26.0
-  - pydantic>=1.0.0
+  - pydantic>=2.1
+  - pydantic-settings
   - msgpack-python
 
     # Testing
diff --git a/devtools/conda-envs/psi-nightly.yaml b/devtools/conda-envs/psi-nightly.yaml
index b175ec049..5b9401d64 100644
--- a/devtools/conda-envs/psi-nightly.yaml
+++ b/devtools/conda-envs/psi-nightly.yaml
@@ -12,7 +12,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.26.0
-  - pydantic>=1.0.0
+  - pydantic>=2.1
+  - pydantic-settings
   - msgpack-python
 
     # Testing
diff --git a/devtools/conda-envs/psi.yaml b/devtools/conda-envs/psi.yaml
index dcff46c1e..7f5e7653c 100644
--- a/devtools/conda-envs/psi.yaml
+++ b/devtools/conda-envs/psi.yaml
@@ -16,7 +16,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental=0.24.0
-  - pydantic=1.8.2  # test minimun stated version.
+  - pydantic>=2.1  # test minimum stated version.
+  - pydantic-settings
   - msgpack-python
 
     # Testing
diff --git a/devtools/conda-envs/qcore.yaml b/devtools/conda-envs/qcore.yaml
index 8e848bc27..a252f3cca 100644
--- a/devtools/conda-envs/qcore.yaml
+++ b/devtools/conda-envs/qcore.yaml
@@ -11,7 +11,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.24
-  - pydantic >=1.8.2
+  - pydantic>=2.1
+  - pydantic-settings
   - tbb<2021
 
     # Testing
diff --git a/devtools/conda-envs/rdkit.yaml b/devtools/conda-envs/rdkit.yaml
index 1ed05aff9..1792a3938 100644
--- a/devtools/conda-envs/rdkit.yaml
+++ b/devtools/conda-envs/rdkit.yaml
@@ -11,7 +11,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.12.0
-  - pydantic>=1.0.0
+  - pydantic>=2.1
+  - pydantic-settings
 
     # Testing
   - pytest
diff --git a/devtools/conda-envs/torchani.yaml b/devtools/conda-envs/torchani.yaml
index 40ba67d10..bfdc2cf2d 100644
--- a/devtools/conda-envs/torchani.yaml
+++ b/devtools/conda-envs/torchani.yaml
@@ -11,7 +11,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.12.0
-  - pydantic>=1.0.0
+  - pydantic>=2.1
+  - pydantic-settings
 
   - pytorch
 
diff --git a/devtools/conda-envs/xtb.yaml b/devtools/conda-envs/xtb.yaml
index fb710e50d..96f9d56b1 100644
--- a/devtools/conda-envs/xtb.yaml
+++ b/devtools/conda-envs/xtb.yaml
@@ -11,7 +11,8 @@ dependencies:
   - py-cpuinfo
   - psutil
   - qcelemental >=0.11.1
-  - pydantic >=1.8.2
+  - pydantic>=2.1
+  - pydantic-settings
 
     # Extras
   - gcp-correction
diff --git a/qcengine/compute.py b/qcengine/compute.py
index 00e94a329..af4754bf4 100644
--- a/qcengine/compute.py
+++ b/qcengine/compute.py
@@ -13,10 +13,7 @@
 from .util import compute_wrapper, environ_context, handle_output_metadata, model_wrapper
 
 if TYPE_CHECKING:
-    try:
-        from pydantic.v1.main import BaseModel
-    except ImportError:
-        from pydantic.main import BaseModel
+    from pydantic.main import BaseModel
     from qcelemental.models import AtomicResult
 
 
diff --git a/qcengine/config.py b/qcengine/config.py
index aa98745f4..72b1d430b 100644
--- a/qcengine/config.py
+++ b/qcengine/config.py
@@ -9,10 +9,8 @@
 import socket
 from typing import Any, Dict, Optional, Union
 
-try:
-    import pydantic.v1 as pydantic
-except ImportError:
-    import pydantic
+from pydantic import BaseModel, ConfigDict, Field
+from pydantic_settings import BaseSettings, SettingsConfigDict
 
 from .extras import get_information
 
@@ -64,7 +62,7 @@ def get_global(key: Optional[str] = None) -> Union[str, Dict[str, Any]]:
         return _global_values[key]
 
 
-class NodeDescriptor(pydantic.BaseModel):
+class NodeDescriptor(BaseModel):
     """
     Description of an individual node
     """
@@ -78,7 +76,7 @@ class NodeDescriptor(pydantic.BaseModel):
     memory_safety_factor: int = 10  # Percentage of memory as a safety factor
 
     # Specifications
-    ncores: Optional[int] = pydantic.Field(
+    ncores: Optional[int] = Field(
         None,
         description="""Number of cores accessible to each task on this node
     
@@ -88,7 +86,7 @@ class NodeDescriptor(pydantic.BaseModel):
     retries: int = 0
 
     # Cluster options
-    is_batch_node: bool = pydantic.Field(
+    is_batch_node: bool = Field(
         False,
         help="""Whether the node running QCEngine is a batch node
     
@@ -103,7 +101,7 @@ class NodeDescriptor(pydantic.BaseModel):
     ``mpiexec_command`` must always be used even for serial jobs (e.g., getting the version number)
     """,
     )
-    mpiexec_command: Optional[str] = pydantic.Field(
+    mpiexec_command: Optional[str] = Field(
         None,
         description="""Invocation for launching node-parallel tasks with MPI
         
@@ -140,31 +138,40 @@ def __init__(self, **data: Dict[str, Any]):
             if "{ranks_per_node}" not in self.mpiexec_command:
                 raise ValueError("mpiexec_command must explicitly state the number of ranks per node")
 
-    class Config:
-        extra = "forbid"
+    model_config = ConfigDict(
+        extra="forbid",
+    )
+
+
+#   class Config:
+#        extra = "forbid"
+#        allow_mutation = False
+#        json_encoders = {np.ndarray: lambda v: v.flatten().tolist(), complex: lambda v: (v.real, v.imag)}
+# ---
+#    model_config = ConfigDict(
+#        extra="forbid",
+#        frozen=True,
+#    )
 
 
-class TaskConfig(pydantic.BaseSettings):
+class TaskConfig(BaseSettings):
     """Description of the configuration used to launch a task."""
 
     # Specifications
-    ncores: int = pydantic.Field(None, description="Number cores per task on each node")
-    nnodes: int = pydantic.Field(None, description="Number of nodes per task")
-    memory: float = pydantic.Field(
-        None, description="Amount of memory in GiB (2^30 bytes; not GB = 10^9 bytes) per node."
-    )
+    ncores: int = Field(None, description="Number cores per task on each node")
+    nnodes: int = Field(None, description="Number of nodes per task")
+    memory: float = Field(None, description="Amount of memory in GiB (2^30 bytes; not GB = 10^9 bytes) per node.")
     scratch_directory: Optional[str]  # What location to use as scratch
     retries: int  # Number of retries on random failures
     mpiexec_command: Optional[str]  # Command used to launch MPI tasks, see NodeDescriptor
     use_mpiexec: bool = False  # Whether it is necessary to use MPI to run an executable
-    cores_per_rank: int = pydantic.Field(1, description="Number of cores per MPI rank")
-    scratch_messy: bool = pydantic.Field(
-        False, description="Leave scratch directory and contents on disk after completion."
-    )
+    cores_per_rank: int = Field(1, description="Number of cores per MPI rank")
+    scratch_messy: bool = Field(False, description="Leave scratch directory and contents on disk after completion.")
 
-    class Config(pydantic.BaseSettings.Config):
-        extra = "forbid"
-        env_prefix = "QCENGINE_"
+    model_config = SettingsConfigDict(
+        extra="forbid",
+        env_prefix="QCENGINE_",
+    )
 
 
 def _load_defaults() -> None:
diff --git a/qcengine/procedures/berny.py b/qcengine/procedures/berny.py
index 84345f203..8c618aeca 100644
--- a/qcengine/procedures/berny.py
+++ b/qcengine/procedures/berny.py
@@ -3,7 +3,7 @@
 import sys
 import traceback
 from io import StringIO
-from typing import Any, Dict, Union
+from typing import Any, ClassVar, Dict, Union
 
 import numpy as np
 from qcelemental.models import OptimizationInput, OptimizationResult, FailedOperation
@@ -16,7 +16,7 @@
 
 
 class BernyProcedure(ProcedureHarness):
-    _defaults = {"name": "Berny", "procedure": "optimization"}
+    _defaults: ClassVar[Dict[str, Any]] = {"name": "Berny", "procedure": "optimization"}
 
     def found(self, raise_error: bool = False) -> bool:
         return which_import(
diff --git a/qcengine/procedures/geometric.py b/qcengine/procedures/geometric.py
index 59bc26c86..d8b19e40a 100644
--- a/qcengine/procedures/geometric.py
+++ b/qcengine/procedures/geometric.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict, Union
+from typing import Any, ClassVar, Dict, Union
 
 from qcelemental.models import OptimizationInput, OptimizationResult
 from qcelemental.util import safe_version, which_import
@@ -8,13 +8,10 @@
 
 class GeometricProcedure(ProcedureHarness):
 
-    _defaults = {"name": "geomeTRIC", "procedure": "optimization"}
+    _defaults: ClassVar[Dict[str, Any]] = {"name": "geomeTRIC", "procedure": "optimization"}
 
     version_cache: Dict[str, str] = {}
 
-    class Config(ProcedureHarness.Config):
-        pass
-
     def found(self, raise_error: bool = False) -> bool:
         return which_import(
             "geometric",
diff --git a/qcengine/procedures/model.py b/qcengine/procedures/model.py
index 0e540114d..e5a334ddf 100644
--- a/qcengine/procedures/model.py
+++ b/qcengine/procedures/model.py
@@ -1,10 +1,7 @@
 import abc
 from typing import Any, Dict, Union
 
-try:
-    from pydantic.v1 import BaseModel
-except ImportError:
-    from pydantic import BaseModel
+from pydantic import BaseModel, ConfigDict
 
 from ..util import model_wrapper
 
@@ -14,9 +11,10 @@ class ProcedureHarness(BaseModel, abc.ABC):
     name: str
     procedure: str
 
-    class Config:
-        allow_mutation: False
-        extra: "forbid"
+    model_config = ConfigDict(
+        frozen=True,
+        extra="forbid",
+    )
 
     def __init__(self, **kwargs):
         super().__init__(**{**self._defaults, **kwargs})
diff --git a/qcengine/procedures/nwchem_opt/__init__.py b/qcengine/procedures/nwchem_opt/__init__.py
index 08baabc50..d9ae29e00 100644
--- a/qcengine/procedures/nwchem_opt/__init__.py
+++ b/qcengine/procedures/nwchem_opt/__init__.py
@@ -1,4 +1,4 @@
-from typing import Union, Dict, Any
+from typing import Any, ClassVar, Dict, Union
 
 from qcelemental.models import OptimizationInput, AtomicInput, OptimizationResult, Provenance
 
@@ -12,10 +12,7 @@
 class NWChemDriverProcedure(ProcedureHarness):
     """Structural relaxation using NWChem's optimizer"""
 
-    _defaults = {"name": "NWChemDriver", "procedure": "optimization"}
-
-    class Config(ProcedureHarness.Config):
-        pass
+    _defaults: ClassVar[Dict[str, Any]] = {"name": "NWChemDriver", "procedure": "optimization"}
 
     def found(self, raise_error: bool = False) -> bool:
         nwc_harness = NWChemHarness()
diff --git a/qcengine/procedures/optking.py b/qcengine/procedures/optking.py
index 91de0ab62..2a0dc06ca 100644
--- a/qcengine/procedures/optking.py
+++ b/qcengine/procedures/optking.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict, Union
+from typing import Any, ClassVar, Dict, Union
 
 from qcelemental.models import OptimizationInput, OptimizationResult
 from qcelemental.util import safe_version, which_import
@@ -8,13 +8,10 @@
 
 class OptKingProcedure(ProcedureHarness):
 
-    _defaults = {"name": "OptKing", "procedure": "optimization"}
+    _defaults: ClassVar[Dict[str, Any]] = {"name": "OptKing", "procedure": "optimization"}
 
     version_cache: Dict[str, str] = {}
 
-    class Config(ProcedureHarness.Config):
-        pass
-
     def found(self, raise_error: bool = False) -> bool:
         return which_import(
             "optking",
diff --git a/qcengine/procedures/torsiondrive.py b/qcengine/procedures/torsiondrive.py
index 0fc1327d7..ad7f88059 100644
--- a/qcengine/procedures/torsiondrive.py
+++ b/qcengine/procedures/torsiondrive.py
@@ -1,7 +1,7 @@
 import io
 from collections import defaultdict
 from contextlib import redirect_stderr, redirect_stdout
-from typing import TYPE_CHECKING, Any, Dict, List, Tuple, Union
+from typing import TYPE_CHECKING, Any, ClassVar, Dict, List, Tuple, Union
 
 import numpy as np
 from qcelemental.models import FailedOperation, Molecule
@@ -16,10 +16,7 @@
 
 class TorsionDriveProcedure(ProcedureHarness):
 
-    _defaults = {"name": "TorsionDrive", "procedure": "torsiondrive"}
-
-    class Config(ProcedureHarness.Config):
-        pass
+    _defaults: ClassVar[Dict[str, Any]] = {"name": "TorsionDrive", "procedure": "torsiondrive"}
 
     def found(self, raise_error: bool = False) -> bool:
         return which_import(
diff --git a/qcengine/programs/adcc.py b/qcengine/programs/adcc.py
index 809503306..252d8f426 100644
--- a/qcengine/programs/adcc.py
+++ b/qcengine/programs/adcc.py
@@ -1,7 +1,7 @@
 """
 Calls adcc
 """
-from typing import TYPE_CHECKING, Dict
+from typing import TYPE_CHECKING, Any, ClassVar, Dict
 
 from qcelemental.models import AtomicResult, BasisSet, Provenance
 from qcelemental.util import safe_version, which_import
@@ -19,7 +19,7 @@
 
 
 class AdccHarness(ProgramHarness):
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "adcc",
         "scratch": False,
         "thread_safe": False,
@@ -29,9 +29,6 @@ class AdccHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         """Whether adcc harness is ready for operation.
diff --git a/qcengine/programs/base.py b/qcengine/programs/base.py
index 8d9cfc9ff..f9c648175 100644
--- a/qcengine/programs/base.py
+++ b/qcengine/programs/base.py
@@ -23,8 +23,9 @@
 from .qcore import EntosHarness, QcoreHarness
 from .rdkit import RDKitHarness
 from .terachem import TeraChemHarness
-from .terachem_frontend import TeraChemFrontEndHarness
-from .terachem_pbs import TeraChemPBSHarness
+
+# from .terachem_frontend import TeraChemFrontEndHarness
+# from .terachem_pbs import TeraChemPBSHarness
 from .torchani import TorchANIHarness
 from .turbomole import TurbomoleHarness
 from .xtb import XTBHarness
@@ -116,8 +117,8 @@ def list_available_programs() -> Set[str]:
 register_program(QcoreHarness())
 register_program(TeraChemHarness())
 register_program(TurbomoleHarness())
-register_program(TeraChemFrontEndHarness())
-register_program(TeraChemPBSHarness())
+# register_program(TeraChemFrontEndHarness())
+# register_program(TeraChemPBSHarness())
 
 # Semi-empirical
 register_program(MopacHarness())
diff --git a/qcengine/programs/cfour/runner.py b/qcengine/programs/cfour/runner.py
index 6fe67e2b6..e181f6db3 100644
--- a/qcengine/programs/cfour/runner.py
+++ b/qcengine/programs/cfour/runner.py
@@ -41,9 +41,6 @@ class CFOURHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         return which(
diff --git a/qcengine/programs/dftd3.py b/qcengine/programs/dftd3.py
index 2f67fcfee..4aff9a1be 100644
--- a/qcengine/programs/dftd3.py
+++ b/qcengine/programs/dftd3.py
@@ -7,7 +7,7 @@
 import socket
 import sys
 from decimal import Decimal
-from typing import TYPE_CHECKING, Any, Dict, Optional, Tuple
+from typing import TYPE_CHECKING, Any, ClassVar, Dict, Optional, Tuple
 
 import numpy as np
 import qcelemental as qcel
@@ -30,7 +30,7 @@
 
 class DFTD3Harness(ProgramHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "DFTD3",
         "scratch": True,
         "thread_safe": True,
@@ -40,9 +40,6 @@ class DFTD3Harness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         return which(
diff --git a/qcengine/programs/dftd_ng.py b/qcengine/programs/dftd_ng.py
index 8fe0af980..870491827 100644
--- a/qcengine/programs/dftd_ng.py
+++ b/qcengine/programs/dftd_ng.py
@@ -7,7 +7,7 @@
 respective dispersion correction.
 """
 
-from typing import Dict
+from typing import Any, ClassVar, Dict
 
 from qcelemental.models import AtomicInput, AtomicResult
 from qcelemental.util import parse_version, safe_version, which_import
@@ -21,7 +21,7 @@
 class DFTD4Harness(ProgramHarness):
     """Calculation harness for the DFT-D4 dispersion correction."""
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "dftd4",
         "scratch": False,
         "thread_safe": True,
@@ -31,9 +31,6 @@ class DFTD4Harness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         """Check for the availability of the Python API of dftd4"""
@@ -185,7 +182,7 @@ class SDFTD3Harness(ProgramHarness):
     it must be explicitly disabled by setting the *s9* value to zero.
     """
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "s-dftd3",
         "scratch": False,
         "thread_safe": True,
@@ -195,9 +192,6 @@ class SDFTD3Harness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         """Check for the availability of the Python API of dftd3"""
diff --git a/qcengine/programs/gamess/runner.py b/qcengine/programs/gamess/runner.py
index b456dbc4d..18a874501 100644
--- a/qcengine/programs/gamess/runner.py
+++ b/qcengine/programs/gamess/runner.py
@@ -42,9 +42,6 @@ class GAMESSHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         return which(
diff --git a/qcengine/programs/gcp.py b/qcengine/programs/gcp.py
index 368f82521..8712ae716 100644
--- a/qcengine/programs/gcp.py
+++ b/qcengine/programs/gcp.py
@@ -7,7 +7,7 @@
 import socket
 import sys
 from decimal import Decimal
-from typing import TYPE_CHECKING, Any, Dict, Optional, Tuple
+from typing import TYPE_CHECKING, Any, ClassVar, Dict, Optional, Tuple
 
 import numpy as np
 import qcelemental as qcel
@@ -29,7 +29,7 @@
 
 class GCPHarness(ProgramHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "GCP",
         "scratch": True,
         "thread_safe": True,
@@ -39,9 +39,6 @@ class GCPHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         return which(
@@ -283,7 +280,7 @@ def parse_output(self, outfiles: Dict[str, str], input_model: "AtomicInput") ->
 
 class MCTCGCPHarness(GCPHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "MCTC-GCP",
         "scratch": True,
         "thread_safe": True,
diff --git a/qcengine/programs/model.py b/qcengine/programs/model.py
index 96e953d10..d5c3e9564 100644
--- a/qcengine/programs/model.py
+++ b/qcengine/programs/model.py
@@ -1,11 +1,8 @@
 import abc
 import logging
-from typing import Any, Dict, List, Optional, Tuple, Union
+from typing import Any, ClassVar, Dict, List, Optional, Tuple, Union
 
-try:
-    from pydantic.v1 import BaseModel
-except ImportError:
-    from pydantic import BaseModel
+from pydantic import BaseModel, ConfigDict
 from qcelemental.models import AtomicInput, AtomicResult, FailedOperation
 
 from qcengine.exceptions import KnownErrorException
@@ -16,18 +13,19 @@
 
 class ProgramHarness(BaseModel, abc.ABC):
 
-    _defaults: Dict[str, Any] = {}
+    _defaults: ClassVar[Dict[str, Any]] = {}
     name: str
     scratch: bool
     thread_safe: bool
     thread_parallel: bool
     node_parallel: bool
     managed_memory: bool
-    extras: Optional[Dict[str, Any]]
+    extras: Optional[Dict[str, Any]] = None
 
-    class Config:
-        allow_mutation: False
-        extra: "forbid"
+    model_config = ConfigDict(
+        frozen=True,
+        extra="forbid",
+    )
 
     def __init__(self, **kwargs):
         super().__init__(**{**self._defaults, **kwargs})
@@ -153,7 +151,9 @@ def compute(self, input_data: AtomicInput, config: TaskConfig) -> AtomicResult:
                 keyword_updates = e.create_keyword_update(local_input_data)
                 new_keywords = local_input_data.keywords.copy()
                 new_keywords.update(keyword_updates)
-                local_input_data = AtomicInput(**local_input_data.dict(exclude={"keywords"}), keywords=new_keywords)
+                local_input_data = AtomicInput(
+                    **local_input_data.model_dump(exclude={"keywords"}), keywords=new_keywords
+                )
 
                 # Store the error details and mitigations employed
                 observed_errors[e.error_name] = {"details": e.details, "keyword_updates": keyword_updates}
diff --git a/qcengine/programs/molpro.py b/qcengine/programs/molpro.py
index 0025ae0f4..09e14a369 100644
--- a/qcengine/programs/molpro.py
+++ b/qcengine/programs/molpro.py
@@ -3,7 +3,7 @@
 """
 
 import string
-from typing import Any, Dict, List, Optional, Set, Tuple
+from typing import Any, ClassVar, Dict, List, Optional, Set, Tuple
 from xml.etree import ElementTree as ET
 
 from qcelemental.models import AtomicResult
@@ -15,7 +15,7 @@
 
 
 class MolproHarness(ProgramHarness):
-    _defaults: Dict[str, Any] = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "Molpro",
         "scratch": True,
         "thread_safe": False,
@@ -63,9 +63,6 @@ class MolproHarness(ProgramHarness):
     # _unrestricted_post_hf_methods: Set[str] = {"UMP2", "UCCSD", "UCCSD(T)"}
     _post_hf_methods: Set[str] = {*_restricted_post_hf_methods}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     def found(self, raise_error: bool = False) -> bool:
         return which(
             "molpro", return_bool=True, raise_error=raise_error, raise_msg="Please install via https://www.molpro.net/"
diff --git a/qcengine/programs/mopac.py b/qcengine/programs/mopac.py
index e97a319c8..06e9bb040 100644
--- a/qcengine/programs/mopac.py
+++ b/qcengine/programs/mopac.py
@@ -2,7 +2,7 @@
 Calls the Psi4 executable.
 """
 import os
-from typing import Any, Dict, List, Optional, Tuple
+from typing import Any, ClassVar, Dict, List, Optional, Tuple
 
 from qcelemental.models import AtomicResult
 from qcelemental.util import which
@@ -14,7 +14,7 @@
 
 class MopacHarness(ProgramHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "MOPAC",
         "scratch": True,  # Input/output file
         "thread_safe": True,
@@ -24,9 +24,6 @@ class MopacHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     def __init__(self, **kwargs):
         extras = {  # All units taken from within MOPAC
             "bohr_to_angstroms": 0.5291772083,
diff --git a/qcengine/programs/mp2d.py b/qcengine/programs/mp2d.py
index 2fd08c8aa..e68578962 100644
--- a/qcengine/programs/mp2d.py
+++ b/qcengine/programs/mp2d.py
@@ -4,7 +4,7 @@
 import re
 import sys
 from decimal import Decimal
-from typing import Any, Dict, Optional, Tuple
+from typing import Any, ClassVar, Dict, Optional, Tuple
 
 import numpy as np
 import qcelemental as qcel
@@ -21,7 +21,7 @@
 
 class MP2DHarness(ProgramHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "MP2D",
         "scratch": True,
         "thread_safe": True,
@@ -31,9 +31,6 @@ class MP2DHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         return which(
diff --git a/qcengine/programs/mrchem.py b/qcengine/programs/mrchem.py
index e52c889ee..67ea582f6 100644
--- a/qcengine/programs/mrchem.py
+++ b/qcengine/programs/mrchem.py
@@ -9,7 +9,7 @@
 from collections import Counter
 from functools import reduce
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, Dict, Optional, Tuple
+from typing import TYPE_CHECKING, Any, ClassVar, Dict, Optional, Tuple
 
 from qcelemental.models import AtomicResult
 from qcelemental.util import safe_version, which
@@ -29,7 +29,7 @@
 
 class MRChemHarness(ProgramHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "MRChem",
         "scratch": False,
         "thread_safe": False,
@@ -39,9 +39,6 @@ class MRChemHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         """Whether MRChem harness is ready for operation.
diff --git a/qcengine/programs/nwchem/runner.py b/qcengine/programs/nwchem/runner.py
index 65a08aa05..15cd186cd 100644
--- a/qcengine/programs/nwchem/runner.py
+++ b/qcengine/programs/nwchem/runner.py
@@ -7,7 +7,7 @@
 import pprint
 import re
 from decimal import Decimal
-from typing import Any, Dict, Optional, Tuple
+from typing import Any, ClassVar, Dict, Optional, Tuple
 
 import numpy as np
 from qcelemental.models import AtomicInput, AtomicResult, BasisSet, Provenance
@@ -39,7 +39,7 @@ class NWChemHarness(ErrorCorrectionProgramHarness):
 
     """
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "NWChem",
         "scratch": True,
         "thread_safe": False,
@@ -50,9 +50,6 @@ class NWChemHarness(ErrorCorrectionProgramHarness):
     # ATL: OpenMP only >=6.6 and only for Phi; potential for Mac using MKL and Intel compilers
     version_cache: Dict[str, str] = {}
 
-    class Config(ErrorCorrectionProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         """Whether NWChem harness is ready for operation, with both the QC program and any particular dependencies found.
@@ -321,7 +318,7 @@ def parse_output(
         build_out(qcvars)
         atprop = build_atomicproperties(qcvars)
 
-        provenance = Provenance(creator="NWChem", version=self.get_version(), routine="nwchem").dict()
+        provenance = Provenance(creator="NWChem", version=self.get_version(), routine="nwchem").model_dump()
         if module is not None:
             provenance["module"] = module
 
@@ -346,4 +343,4 @@ def parse_output(
             k.upper(): str(v) if isinstance(v, Decimal) else v for k, v in qcvars.items()
         }
 
-        return AtomicResult(**{**input_model.dict(), **output_data})
+        return AtomicResult(**{**input_model.model_dump(), **output_data})
diff --git a/qcengine/programs/openmm.py b/qcengine/programs/openmm.py
index bb54567b3..7a2038b2d 100644
--- a/qcengine/programs/openmm.py
+++ b/qcengine/programs/openmm.py
@@ -6,7 +6,7 @@
 import datetime
 import hashlib
 import os
-from typing import TYPE_CHECKING, Dict
+from typing import TYPE_CHECKING, Any, ClassVar, Dict
 
 import numpy as np
 from qcelemental.models import AtomicResult, BasisSet, Provenance
@@ -28,7 +28,7 @@ class OpenMMHarness(ProgramHarness):
     _CACHE = {}
     _CACHE_MAX_SIZE = 10
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "OpenMM",
         "scratch": True,
         "thread_safe": True,  # true if we use separate `openmm.Context` objects per thread
@@ -39,9 +39,6 @@ class OpenMMHarness(ProgramHarness):
 
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     # def _get_off_forcefield(self, hashstring, offxml):
     #
     #     from openff.toolkit.typing.engines import smirnoff
diff --git a/qcengine/programs/psi4.py b/qcengine/programs/psi4.py
index 99b725c64..5080e9c54 100644
--- a/qcengine/programs/psi4.py
+++ b/qcengine/programs/psi4.py
@@ -5,7 +5,7 @@
 import os
 import sys
 from pathlib import Path
-from typing import TYPE_CHECKING, Dict
+from typing import TYPE_CHECKING, Any, ClassVar, Dict
 
 from qcelemental.models import AtomicResult, BasisSet
 from qcelemental.util import deserialize, parse_version, safe_version, which, which_import
@@ -22,7 +22,7 @@
 
 class Psi4Harness(ProgramHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "Psi4",
         "scratch": True,
         "thread_safe": False,
@@ -32,9 +32,6 @@ class Psi4Harness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         """Whether Psi4 harness is ready for operation.
diff --git a/qcengine/programs/qchem.py b/qcengine/programs/qchem.py
index 79a03bdc8..22aeb406f 100644
--- a/qcengine/programs/qchem.py
+++ b/qcengine/programs/qchem.py
@@ -7,7 +7,7 @@
 import tempfile
 import warnings
 from collections import defaultdict
-from typing import Any, Dict, List, Optional, Tuple
+from typing import Any, ClassVar, Dict, List, Optional, Tuple
 
 import numpy as np
 from qcelemental import constants
@@ -25,7 +25,7 @@
 
 
 class QChemHarness(ProgramHarness):
-    _defaults: Dict[str, Any] = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "QChem",
         "scratch": True,
         "thread_safe": False,
diff --git a/qcengine/programs/qcore.py b/qcengine/programs/qcore.py
index 172f8dbb7..b8a51ebdb 100644
--- a/qcengine/programs/qcore.py
+++ b/qcengine/programs/qcore.py
@@ -2,7 +2,7 @@
 The qcore QCEngine Harness
 """
 
-from typing import TYPE_CHECKING, Any, Dict, List, Set
+from typing import TYPE_CHECKING, Any, ClassVar, Dict, List, Set
 
 import numpy as np
 from qcelemental.models import AtomicResult, BasisSet
@@ -31,7 +31,7 @@ def qcore_ao_order_spherical(max_angular_momentum: int) -> Dict[int, List[int]]:
 
 
 class QcoreHarness(ProgramHarness):
-    _defaults: Dict[str, Any] = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "Qcore",
         "scratch": False,
         "thread_safe": False,
@@ -88,9 +88,6 @@ class QcoreHarness(ProgramHarness):
     # Entos spherical basis ordering for each angular momentum. Follows reverse order of CCA.
     _qcore_to_cca_ao_order = {"spherical": get_ao_conversion(cca_ao_order_spherical(10), qcore_ao_order_spherical(10))}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     def found(self, raise_error: bool = False) -> bool:
         return which_import(
             "qcore",
@@ -250,7 +247,7 @@ def parse_output(self, output: Dict[str, Any], input_model: "AtomicInput") -> "A
 
 
 class EntosHarness(QcoreHarness):
-    _defaults: Dict[str, Any] = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "Entos",
         "scratch": True,
         "thread_safe": False,
diff --git a/qcengine/programs/rdkit.py b/qcengine/programs/rdkit.py
index 1a01a0253..a78c66137 100644
--- a/qcengine/programs/rdkit.py
+++ b/qcengine/programs/rdkit.py
@@ -2,7 +2,7 @@
 Calls the RDKit package.
 """
 
-from typing import TYPE_CHECKING, Dict
+from typing import TYPE_CHECKING, Any, ClassVar, Dict
 
 from qcelemental.models import AtomicResult, Provenance
 from qcelemental.util import safe_version, which_import
@@ -19,7 +19,7 @@
 
 class RDKitHarness(ProgramHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "RDKit",
         "scratch": False,
         "thread_safe": True,
@@ -30,9 +30,6 @@ class RDKitHarness(ProgramHarness):
 
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def _process_molecule_rdkit(jmol):
         from rdkit import Chem
diff --git a/qcengine/programs/terachem.py b/qcengine/programs/terachem.py
index 98dfcaabe..05f6ed727 100644
--- a/qcengine/programs/terachem.py
+++ b/qcengine/programs/terachem.py
@@ -3,7 +3,7 @@
 """
 
 import re
-from typing import Any, Dict, Optional
+from typing import Any, ClassVar, Dict, Optional
 
 from qcelemental.models import AtomicResult, FailedOperation
 from qcelemental.molparse.regex import DECIMAL, NUMBER
@@ -18,7 +18,7 @@
 
 class TeraChemHarness(ProgramHarness):
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "TeraChem",
         "scratch": True,
         "thread_safe": False,
@@ -28,9 +28,6 @@ class TeraChemHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         return which(
diff --git a/qcengine/programs/terachem_frontend.py b/qcengine/programs/terachem_frontend.py
index 09b8503a3..5d1ab0d6d 100644
--- a/qcengine/programs/terachem_frontend.py
+++ b/qcengine/programs/terachem_frontend.py
@@ -1,7 +1,7 @@
 """Harness for TeraChem Frontend"""
 import logging
 from os import getenv
-from typing import Any, Dict
+from typing import Any, ClassVar, Dict
 
 from .terachem_pbs import TeraChemPBSHarness, _pbs_defaults
 
diff --git a/qcengine/programs/terachem_pbs.py b/qcengine/programs/terachem_pbs.py
index 4cee0a31e..26010d504 100644
--- a/qcengine/programs/terachem_pbs.py
+++ b/qcengine/programs/terachem_pbs.py
@@ -4,7 +4,7 @@
 import logging
 from importlib import import_module
 from os import getenv
-from typing import TYPE_CHECKING, Any, Dict, Union
+from typing import TYPE_CHECKING, Any, ClassVar, Dict, Union
 
 from qcelemental.models import AtomicResult, FailedOperation
 from qcelemental.util import which_import
@@ -31,7 +31,7 @@
 class TeraChemPBSHarness(ProgramHarness):
     """QCEngine Harness for interfacing with the TeraChem running in Protocol Buffer Server Mode"""
 
-    _defaults = _pbs_defaults
+    _defaults: ClassVar[Dict[str, Any]] = _pbs_defaults
     _tcpb_package: str = "tcpb"
     _tcpb_min_version: str = "0.7.0"
     _tcpb_client: str = "TCProtobufClient"
@@ -41,9 +41,6 @@ class TeraChemPBSHarness(ProgramHarness):
     }
     _env_vars_external: str = "TERACHEM_PBS_HOST, TERACHEM_PBS_PORT"
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @classmethod
     def found(cls, raise_error: bool = False) -> bool:
         """Whether TeraChemPBS harness is ready for operation.
diff --git a/qcengine/programs/torchani.py b/qcengine/programs/torchani.py
index 2e81a5d9e..c8ea19b0a 100644
--- a/qcengine/programs/torchani.py
+++ b/qcengine/programs/torchani.py
@@ -2,7 +2,7 @@
 Calls the TorchANI package.
 """
 
-from typing import TYPE_CHECKING, Dict
+from typing import TYPE_CHECKING, Any, ClassVar, Dict
 
 from qcelemental.models import AtomicResult, Provenance
 from qcelemental.util import parse_version, safe_version, which_import
@@ -21,7 +21,7 @@ class TorchANIHarness(ProgramHarness):
 
     _CACHE = {}
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "TorchANI",
         "scratch": False,
         "thread_safe": True,
@@ -31,9 +31,6 @@ class TorchANIHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         return which_import(
diff --git a/qcengine/programs/xtb.py b/qcengine/programs/xtb.py
index d9114b54d..7cf6b6196 100644
--- a/qcengine/programs/xtb.py
+++ b/qcengine/programs/xtb.py
@@ -9,7 +9,7 @@
 visit `its documentation <https://xtb-python.readthedocs.io>`_.
 """
 
-from typing import Dict
+from typing import Any, ClassVar, Dict
 
 from qcelemental.models import AtomicInput, AtomicResult
 from qcelemental.util import safe_version, which_import
@@ -21,7 +21,7 @@
 class XTBHarness(ProgramHarness):
     """Calculation harness for the extended tight binding (xtb) package."""
 
-    _defaults = {
+    _defaults: ClassVar[Dict[str, Any]] = {
         "name": "xtb",
         "scratch": False,
         "thread_safe": True,
@@ -31,9 +31,6 @@ class XTBHarness(ProgramHarness):
     }
     version_cache: Dict[str, str] = {}
 
-    class Config(ProgramHarness.Config):
-        pass
-
     @staticmethod
     def found(raise_error: bool = False) -> bool:
         """Check for the availability of the Python API of xtb"""
diff --git a/qcengine/testing.py b/qcengine/testing.py
index 3f7ff1ff7..5304a4e90 100644
--- a/qcengine/testing.py
+++ b/qcengine/testing.py
@@ -9,6 +9,7 @@
 import qcelemental as qcel
 from pkg_resources import parse_version
 from qcelemental.util import which, which_import
+from pydantic import ConfigDict
 
 import qcengine as qcng
 
@@ -95,8 +96,9 @@ class FailEngine(qcng.programs.ProgramHarness):
             "managed_memory": False,
         }
 
-        class Config(qcng.programs.ProgramHarness.Config):
-            allow_mutation: True
+        model_config = ConfigDict(
+            frozen=False,
+        )
 
         @staticmethod
         def found(raise_error: bool = False) -> bool:
diff --git a/qcengine/tests/test_config.py b/qcengine/tests/test_config.py
index bae420d7b..4a7cef8f0 100644
--- a/qcengine/tests/test_config.py
+++ b/qcengine/tests/test_config.py
@@ -4,10 +4,7 @@
 
 import copy
 
-try:
-    import pydantic.v1 as pydantic
-except ImportError:
-    import pydantic
+import pydantic
 import pytest
 
 import qcengine as qcng
diff --git a/qcengine/util.py b/qcengine/util.py
index 352193885..c0700c2ea 100644
--- a/qcengine/util.py
+++ b/qcengine/util.py
@@ -18,10 +18,7 @@
 from threading import Thread
 from typing import Any, BinaryIO, Dict, List, Optional, TextIO, Tuple, Union
 
-try:
-    from pydantic.v1 import BaseModel, ValidationError
-except ImportError:
-    from pydantic import BaseModel, ValidationError
+from pydantic import BaseModel, ValidationError
 from qcelemental.models import AtomicResult, FailedOperation, OptimizationResult
 
 from qcengine.config import TaskConfig
diff --git a/setup.py b/setup.py
index 92965b94c..0fdae913a 100644
--- a/setup.py
+++ b/setup.py
@@ -28,7 +28,7 @@
         cmdclass=versioneer.get_cmdclass(),
         packages=setuptools.find_packages(),
         setup_requires=[] + pytest_runner,
-        install_requires=["pyyaml", "py-cpuinfo", "psutil", "qcelemental>=0.24.0,<0.27.0", "pydantic>=1.8.2"],
+        install_requires=["pyyaml", "py-cpuinfo", "psutil", "qcelemental>=0.26.0", "pydantic>=2.1.0, pydantic-settings"],
         entry_points={"console_scripts": ["qcengine=qcengine.cli:main"]},
         extras_require={
             "docs": [