diff --git a/antarest/launcher/service.py b/antarest/launcher/service.py
index 824bfc75b0..ee193cadd8 100644
--- a/antarest/launcher/service.py
+++ b/antarest/launcher/service.py
@@ -228,7 +228,7 @@ def run_study(
         job_uuid = self._generate_new_id()
         logger.info(f"New study launch (study={study_uuid}, job_id={job_uuid})")
         study_info = self.study_service.get_study_information(uuid=study_uuid, params=params)
-        solver_version = study_version or study_info.version.__format__(format_spec="ddd")
+        solver_version = study_version or study_info.version.__str__()
 
         self._assert_launcher_is_initialized(launcher)
         assert_permission(
diff --git a/antarest/study/business/areas/st_storage_management.py b/antarest/study/business/areas/st_storage_management.py
index da4d99c231..0c150b3e95 100644
--- a/antarest/study/business/areas/st_storage_management.py
+++ b/antarest/study/business/areas/st_storage_management.py
@@ -394,7 +394,7 @@ def update_storages_props(
 
                 # Convert the DTO to a configuration object and update the configuration file.
                 properties = create_st_storage_config(
-                    study.version, **new_cluster.model_dump(by_alias=False, exclude_none=True)
+                    StudyVersion.parse(study.version), **new_cluster.model_dump(by_alias=False, exclude_none=True)
                 )
                 path = _STORAGE_LIST_PATH.format(area_id=area_id, storage_id=storage_id)
                 cmd = UpdateConfig(
diff --git a/antarest/study/business/areas/thermal_management.py b/antarest/study/business/areas/thermal_management.py
index daafde3608..a9c5bb924b 100644
--- a/antarest/study/business/areas/thermal_management.py
+++ b/antarest/study/business/areas/thermal_management.py
@@ -463,7 +463,7 @@ def validate_series(self, study: Study, area_id: str, cluster_id: str) -> bool:
         lower_cluster_id = cluster_id.lower()
         thermal_cluster_path = Path(f"input/thermal/series/{area_id}/{lower_cluster_id}")
         series_path = [thermal_cluster_path / "series"]
-        if StudyVersion(study.version) >= 870:
+        if StudyVersion.parse(study.version) >= 870:
             series_path.append(thermal_cluster_path / "CO2Cost")
             series_path.append(thermal_cluster_path / "fuelCost")
 
diff --git a/antarest/study/model.py b/antarest/study/model.py
index ba4b6603d0..9c80c32b7e 100644
--- a/antarest/study/model.py
+++ b/antarest/study/model.py
@@ -359,8 +359,8 @@ class StudyMetadataDTO(BaseModel):
     folder: t.Optional[str] = None
     tags: t.List[str] = []
 
-    @field_serializer('version', when_used='json')
-    def serialize_version(self, version: StudyVersion):
+    @field_serializer('version')
+    def serialize_version(self, version: StudyVersion) -> int:
         return version.__int__()
 
     @field_validator("horizon", mode="before")
diff --git a/antarest/study/storage/rawstudy/model/filesystem/config/files.py b/antarest/study/storage/rawstudy/model/filesystem/config/files.py
index df1c32fb22..249560556e 100644
--- a/antarest/study/storage/rawstudy/model/filesystem/config/files.py
+++ b/antarest/study/storage/rawstudy/model/filesystem/config/files.py
@@ -199,7 +199,7 @@ def _parse_version(path: Path) -> StudyVersion:
         inside_root_path=Path("study.antares"),
         file_type=FileType.SIMPLE_INI,
     )
-    version = study_info.get("antares", {}).get("version", -1)
+    version = study_info.get("antares", {}).get("version", 0)
     return StudyVersion.parse(version)
 
 
diff --git a/antarest/study/storage/rawstudy/model/filesystem/config/model.py b/antarest/study/storage/rawstudy/model/filesystem/config/model.py
index ef92d19a19..aea8bb0640 100644
--- a/antarest/study/storage/rawstudy/model/filesystem/config/model.py
+++ b/antarest/study/storage/rawstudy/model/filesystem/config/model.py
@@ -15,7 +15,7 @@
 from pathlib import Path
 
 from antares.study.version import StudyVersion
-from pydantic import BaseModel, Field, model_validator
+from pydantic import BaseModel, Field, model_validator, field_serializer, field_validator
 
 from antarest.core.utils.utils import DTO
 from antarest.study.business.enum_ignore_case import EnumIgnoreCase
@@ -318,6 +318,15 @@ class FileStudyTreeConfigDTO(BaseModel):
     enr_modelling: str = str(EnrModelling.AGGREGATED)
     zip_path: t.Optional[Path] = None
 
+    @field_serializer('version')
+    def serialize_version(self, version: StudyVersion) -> int:
+        return version.__int__()
+
+    @field_validator("version", mode="before")
+    def _validate_version(cls, v: t.Any) -> StudyVersion:
+        return StudyVersion.parse(v)
+
+
     @staticmethod
     def from_build_config(
         config: FileStudyTreeConfig,
diff --git a/tests/cache/test_local_cache.py b/tests/cache/test_local_cache.py
index a643be4c62..3242d92533 100644
--- a/tests/cache/test_local_cache.py
+++ b/tests/cache/test_local_cache.py
@@ -28,7 +28,7 @@ def test_lifecycle():
         study_path=Path("somepath"),
         path=Path("somepath"),
         study_id="",
-        version=StudyVersion.parse(-1),
+        version=StudyVersion.parse(0),
         areas={
             "a1": Area(
                 name="a1",
diff --git a/tests/cache/test_redis_cache.py b/tests/cache/test_redis_cache.py
index f17faa6f9a..f5fe9c37a3 100644
--- a/tests/cache/test_redis_cache.py
+++ b/tests/cache/test_redis_cache.py
@@ -27,7 +27,7 @@ def test_lifecycle():
         study_path=Path("somepath"),
         path=Path("somepath"),
         study_id="",
-        version=StudyVersion.parse(-1),
+        version=StudyVersion.parse(0),
         areas={
             "a1": Area(
                 name="a1",
diff --git a/tests/storage/business/test_raw_study_service.py b/tests/storage/business/test_raw_study_service.py
index 9364edfa14..2e9bb25c5a 100644
--- a/tests/storage/business/test_raw_study_service.py
+++ b/tests/storage/business/test_raw_study_service.py
@@ -621,7 +621,7 @@ def test_check_and_update_study_version_in_database(tmp_path: Path) -> None:
 
     assert raw_study.version == "100"
 
-    raw_study = RawStudy(id=name, workspace="foo", path=str(study_path), version="100")
+    raw_study = RawStudy(id=name, workspace="foo", path=str(study_path), version="42")
 
     file_study_tree = Mock()
     file_study_tree.get.return_value = {"version": 42}
diff --git a/tests/storage/business/test_study_version_upgrader.py b/tests/storage/business/test_study_version_upgrader.py
index 4fa7e940ec..979f38d064 100644
--- a/tests/storage/business/test_study_version_upgrader.py
+++ b/tests/storage/business/test_study_version_upgrader.py
@@ -124,15 +124,15 @@ def test_fails_because_of_versions_asked(tmp_path: Path):
     with zipfile.ZipFile(path_study) as zip_output:
         zip_output.extractall(path=study_dir)
     # Try to upgrade with an unknown version
-    with pytest.raises(InvalidUpgrade, match="Cannot downgrade from version '7.2' to '6'"):
+    with pytest.raises(InvalidUpgrade, match="Cannot downgrade from version '720' to '600'"):
         StudyUpgrader(study_dir, "600").upgrade()
     # Try to upgrade with the current version
-    with pytest.raises(InvalidUpgrade, match="Your study is already in version '7.2'"):
+    with pytest.raises(InvalidUpgrade, match="Your study is already in version '720'"):
         StudyUpgrader(study_dir, "720").upgrade()
     # Try to upgrade with an old version
     with pytest.raises(
         InvalidUpgrade,
-        match="Cannot downgrade from version '7.2' to '7.1'",
+        match="Cannot downgrade from version '720' to '710'",
     ):
         StudyUpgrader(study_dir, "710").upgrade()
     # Try to upgrade with a version that does not exist
diff --git a/tests/storage/repository/filesystem/config/test_config_files.py b/tests/storage/repository/filesystem/config/test_config_files.py
index a0fdf6d4f5..77ae462678 100644
--- a/tests/storage/repository/filesystem/config/test_config_files.py
+++ b/tests/storage/repository/filesystem/config/test_config_files.py
@@ -81,7 +81,7 @@ def test_parse_output_parameters(study_path: Path) -> None:
     config = FileStudyTreeConfig(
         study_path=study_path,
         path=study_path,
-        version=-1,
+        version=0,
         store_new_set=True,
         study_id="id",
         output_path=study_path / "output",
@@ -105,7 +105,7 @@ def test_parse_bindings(study_path: Path) -> None:
     config = FileStudyTreeConfig(
         study_path=study_path,
         path=study_path,
-        version=-1,
+        version=0,
         bindings=[
             BindingConstraintDTO(
                 id="bindA",
@@ -154,7 +154,7 @@ def test_parse_outputs(study_path: Path) -> None:
         study_path=study_path,
         path=study_path,
         study_id="id",
-        version=-1,
+        version=0,
         output_path=study_path / "output",
         outputs={
             "20201220-1456eco-hello": Simulation(
@@ -271,7 +271,7 @@ def test_parse_area(study_path: Path) -> None:
         study_path=study_path,
         path=study_path,
         study_id="id",
-        version=-1,
+        version=0,
         output_path=study_path / "output",
         areas={
             "fr": Area(
@@ -307,7 +307,7 @@ def test_parse_area__extra_area(study_path: Path) -> None:
         study_path=study_path,
         path=study_path,
         study_id="id",
-        version=-1,
+        version=0,
         output_path=study_path / "output",
         areas={
             "fr": Area(