diff --git a/HISTORY.md b/HISTORY.md
index 032874f..16f36ca 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,4 +1,7 @@
 # History
+## v4.0.0 (26-12-25)
+* Upgrades Pydantic API from V1 to V2
+
 ## v3.3.0 (18-09-25)
 * Drops python 3.8 and 3.9. Moves to 3.10 as minimum
 * Drops poetry package management. Replaces with uv
diff --git a/dicomtrolley/core.py b/dicomtrolley/core.py
index 7c677ee..f64f7f6 100644
--- a/dicomtrolley/core.py
+++ b/dicomtrolley/core.py
@@ -13,7 +13,7 @@
     TypeVar,
 )
 
-from pydantic import Field, ValidationError, field_validator
+from pydantic import ConfigDict, Field, ValidationError, field_validator
 from pydantic.main import BaseModel
 from pydicom.datadict import tag_for_keyword
 from pydicom.dataset import Dataset
@@ -187,8 +187,8 @@ class DICOMObject(BaseModel, DICOMDownloadable):
     a DICOM dataset
     """
 
-    class Config:
-        arbitrary_types_allowed = True  # allows the use of Dataset type below
+    # allows the use of Dataset type below
+    model_config = ConfigDict(arbitrary_types_allowed=True)
 
     uid: str
     data: Dataset
@@ -614,9 +614,8 @@ class Query(BaseModel):
     max_study_date: Optional[datetime] = None
     min_study_date: Optional[datetime] = None
     include_fields: Optional[List[str]] = Field(default_factory=list)
-
-    class Config:
-        extra = "forbid"  # raise ValueError when passing an unknown keyword to init
+    # raise ValueError when passing an unknown keyword to init
+    model_config = ConfigDict(extra="forbid")
 
     @classmethod
     def init_from_query(
@@ -643,7 +642,7 @@ def init_from_query(
             this class
         """
         # remove empty, None and 0 values
-        params = {key: val for key, val in query.dict().items() if val}
+        params = {key: val for key, val in query.model_dump().items() if val}
         try:
             return cls(**params)
         except ValidationError as e:
@@ -672,7 +671,9 @@ def include_fields_check(cls, include_fields, values):  # noqa: B902, N805
 
     def to_short_string(self):
         """A more information-dense str repr. For human reading"""
-        filled_fields = {key: val for key, val in self.dict().items() if val}
+        filled_fields = {
+            key: val for key, val in self.model_dump().items() if val
+        }
         filled_fields["query_level"] = filled_fields["query_level"].value
         return f"{type(self).__name__}: {filled_fields}"
 
diff --git a/dicomtrolley/dicom_qr.py b/dicomtrolley/dicom_qr.py
index 1f97d1b..95c33ed 100644
--- a/dicomtrolley/dicom_qr.py
+++ b/dicomtrolley/dicom_qr.py
@@ -5,6 +5,7 @@
 
 from typing import Dict, List
 
+from pydantic import ConfigDict
 from pydicom.datadict import tag_for_keyword
 from pydicom.dataset import Dataset
 from pynetdicom import AE, debug_logger
@@ -59,9 +60,8 @@ class DICOMQuery(ExtendedQuery):
     Modality: str = ""
     ProtocolName: str = ""
     StudyID: str = ""
-
-    class Config:
-        extra = "forbid"  # raise ValueError when passing an unknown keyword to init
+    # raise ValueError when passing an unknown keyword to init
+    model_config = ConfigDict(extra="forbid")
 
     @staticmethod
     def get_default_include_fields(query_level):
@@ -95,7 +95,7 @@ def as_parameters(self) -> Dict[str, str]:
 
         # remove non-DICOM parameters and replace with DICOM tags based on them
         parameters = {
-            x: y for x, y in self.dict().items()
+            x: y for x, y in self.model_dump().items()
         }  # all params for query
         parameters["StudyDate"] = self.get_study_date(
             parameters.pop("min_study_date"), parameters.pop("max_study_date")
diff --git a/dicomtrolley/mint.py b/dicomtrolley/mint.py
index a89f014..8aaa425 100644
--- a/dicomtrolley/mint.py
+++ b/dicomtrolley/mint.py
@@ -160,10 +160,10 @@ class MintQuery(ExtendedQuery):
     limit: int = 0  # how many results to return. 0 = all
 
     @model_validator(mode="after")
-    def min_max_study_date_xor(cls, values):  # noqa: B902, N805
+    def min_max_study_date_xor(self):  # noqa: B902, N805
         """Min and max should both be given or both be empty"""
-        min_date = values.min_study_date
-        max_date = values.max_study_date
+        min_date = self.min_study_date
+        max_date = self.max_study_date
         if min_date and not max_date:
             raise ValueError(
                 f"min_study_date parameter was passed"
@@ -175,7 +175,7 @@ def min_max_study_date_xor(cls, values):  # noqa: B902, N805
                 f"max_study_date parameter was passed ({max_date}), "
                 f"but min_study_date was not. Both need to be given"
             )
-        return values
+        return self
 
     @model_validator(mode="after")
     def include_fields_check(self):
@@ -204,7 +204,7 @@ def __str__(self):
 
     def as_parameters(self):
         """All non-empty query parameters. For use as url parameters"""
-        parameters = {x: y for x, y in self.dict().items() if y}
+        parameters = {x: y for x, y in self.model_dump().items() if y}
 
         if "min_study_date" in parameters:
             parameters["min_study_date"] = parameters[
@@ -332,6 +332,6 @@ def parse_attribs(element):
     return dataset
 
 
-MintInstance.update_forward_refs()  # enables pydantic validation
-MintSeries.update_forward_refs()
-MintStudy.update_forward_refs()
+MintInstance.model_rebuild()  # enables pydantic validation
+MintSeries.model_rebuild()
+MintStudy.model_rebuild()
diff --git a/dicomtrolley/qido_rs.py b/dicomtrolley/qido_rs.py
index ef8ad28..955aa53 100644
--- a/dicomtrolley/qido_rs.py
+++ b/dicomtrolley/qido_rs.py
@@ -132,7 +132,7 @@ def uri_search_params(self) -> Dict[str, Union[str, List[str]]]:
         }
         other_search_params = {
             key: val
-            for key, val in self.dict().items()
+            for key, val in self.model_dump().items()
             if key not in exclude_fields
         }
 
@@ -182,7 +182,7 @@ def assert_parents_filled(a_hierarchy, value_dict):
             else:
                 return assert_parents_filled(a_hierarchy, value_dict)
 
-        assert_parents_filled(order, self.dict())
+        assert_parents_filled(order, self.model_dump())
         return self
 
     @model_validator(mode="after")
@@ -198,7 +198,7 @@ def assert_key_exists(values_in, query_level_in, missing_key_in):
                     f"a QIDO-RS relational query"
                 )
 
-        values = self.dict()
+        values = self.model_dump()
         if query_level == QueryLevels.STUDY:
             pass  # Fine. you can always look for some studies
         elif query_level == QueryLevels.SERIES:
diff --git a/pyproject.toml b/pyproject.toml
index d820cf9..032de22 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "dicomtrolley"
-version = "3.3.0"
+version = "4.0.0"
 description = "Retrieve medical images via WADO-URI, WADO-RS, QIDO-RS, MINT, RAD69 and DICOM-QR"
 authors = [{name="Sjoerd Kerkstra", email ="sjoerd.kerkstra@radboudumc.nl"}]
 readme = "README.md"