diff --git a/apps/hash-graph/libs/graph/src/store/validation.rs b/apps/hash-graph/libs/graph/src/store/validation.rs
index 20035a47ea9..47bf6e68c9e 100644
--- a/apps/hash-graph/libs/graph/src/store/validation.rs
+++ b/apps/hash-graph/libs/graph/src/store/validation.rs
@@ -160,6 +160,8 @@ where
     C: AsClient,
     A: AuthorizationApi,
 {
+    type Value = Arc<DataTypeWithMetadata>;
+
     #[expect(refining_impl_trait)]
     async fn provide_type(
         &self,
@@ -345,6 +347,8 @@ where
     C: AsClient,
     A: AuthorizationApi,
 {
+    type Value = Arc<PropertyType>;
+
     #[expect(refining_impl_trait)]
     async fn provide_type(
         &self,
@@ -464,6 +468,8 @@ where
     C: AsClient,
     A: AuthorizationApi,
 {
+    type Value = Arc<ClosedEntityType>;
+
     #[expect(refining_impl_trait)]
     async fn provide_type(
         &self,
diff --git a/apps/hash-graph/libs/store/src/filter/mod.rs b/apps/hash-graph/libs/store/src/filter/mod.rs
index 8cb7e458204..e8082170a70 100644
--- a/apps/hash-graph/libs/store/src/filter/mod.rs
+++ b/apps/hash-graph/libs/store/src/filter/mod.rs
@@ -519,6 +519,8 @@ mod tests {
 
     #[expect(refining_impl_trait)]
     impl OntologyTypeProvider<DataTypeWithMetadata> for TestDataTypeProvider {
+        type Value = DataTypeWithMetadata;
+
         async fn provide_type(&self, _: &VersionedUrl) -> Result<DataTypeWithMetadata, Report<!>> {
             unimplemented!()
         }
diff --git a/libs/@blockprotocol/type-system/rust/src/schema/data_type/mod.rs b/libs/@blockprotocol/type-system/rust/src/schema/data_type/mod.rs
index c78d1e5e1de..fa61374ccb8 100644
--- a/libs/@blockprotocol/type-system/rust/src/schema/data_type/mod.rs
+++ b/libs/@blockprotocol/type-system/rust/src/schema/data_type/mod.rs
@@ -132,6 +132,9 @@ mod raw {
         )]
         #[serde(default, skip_serializing_if = "Vec::is_empty")]
         all_of: Vec<DataTypeReference>,
+
+        #[serde(default)]
+        r#abstract: bool,
     }
 
     #[derive(Deserialize)]
@@ -194,6 +197,7 @@ mod raw {
                 title: common.title,
                 title_plural: common.title_plural,
                 all_of: common.all_of,
+                r#abstract: common.r#abstract,
                 constraints,
             }
         }
@@ -214,6 +218,7 @@ pub struct DataType {
     #[serde(skip_serializing_if = "Vec::is_empty")]
     pub all_of: Vec<DataTypeReference>,
 
+    pub r#abstract: bool,
     #[serde(flatten)]
     pub constraints: ValueConstraints,
 }
diff --git a/libs/@local/hash-graph-types/rust/src/knowledge/property/visitor.rs b/libs/@local/hash-graph-types/rust/src/knowledge/property/visitor.rs
index 9c5d937c8bf..5d6d9e16670 100644
--- a/libs/@local/hash-graph-types/rust/src/knowledge/property/visitor.rs
+++ b/libs/@local/hash-graph-types/rust/src/knowledge/property/visitor.rs
@@ -60,6 +60,8 @@ pub enum TraversalError {
         actual: VersionedUrl,
         expected: VersionedUrl,
     },
+    #[error("Values cannot be assigned to an abstract data type. `{id}` is abstract.")]
+    AbstractDataType { id: VersionedUrl },
     #[error("the value provided does not match the constraints of the data type")]
     ConstraintUnfulfilled,
     #[error("the property `{key}` was required, but not specified")]
diff --git a/libs/@local/hash-graph-types/rust/src/lib.rs b/libs/@local/hash-graph-types/rust/src/lib.rs
index 0c4f5f2cf6d..af7ece07d02 100644
--- a/libs/@local/hash-graph-types/rust/src/lib.rs
+++ b/libs/@local/hash-graph-types/rust/src/lib.rs
@@ -2,7 +2,6 @@
 #![feature(hash_raw_entry)]
 
 extern crate alloc;
-extern crate core;
 
 pub mod knowledge;
 pub mod ontology;
diff --git a/libs/@local/hash-graph-types/rust/src/ontology/mod.rs b/libs/@local/hash-graph-types/rust/src/ontology/mod.rs
index d2009a13f9b..0afcc580e8a 100644
--- a/libs/@local/hash-graph-types/rust/src/ontology/mod.rs
+++ b/libs/@local/hash-graph-types/rust/src/ontology/mod.rs
@@ -169,10 +169,12 @@ pub struct OntologyTypeWithMetadata<S: OntologyType> {
 }
 
 pub trait OntologyTypeProvider<O> {
+    type Value: Borrow<O> + Send;
+
     fn provide_type(
         &self,
         type_id: &VersionedUrl,
-    ) -> impl Future<Output = Result<impl Borrow<O> + Send, Report<impl Context>>> + Send;
+    ) -> impl Future<Output = Result<Self::Value, Report<impl Context>>> + Send;
 }
 
 pub trait DataTypeProvider: OntologyTypeProvider<DataTypeWithMetadata> {
diff --git a/libs/@local/hash-validation/src/entity_type.rs b/libs/@local/hash-validation/src/entity_type.rs
index d109e0367aa..90f8af6352c 100644
--- a/libs/@local/hash-validation/src/entity_type.rs
+++ b/libs/@local/hash-validation/src/entity_type.rs
@@ -267,17 +267,30 @@ impl EntityVisitor for ValueValidator {
         &mut self,
         data_type: &DataTypeWithMetadata,
         value: &mut JsonValue,
-        _: &mut ValueMetadata,
+        metadata: &mut ValueMetadata,
         _: &P,
     ) -> Result<(), Report<[TraversalError]>>
     where
         P: DataTypeProvider + Sync,
     {
-        data_type
-            .schema
-            .validate_constraints(value)
-            .change_context(TraversalError::ConstraintUnfulfilled)
-            .map_err(Report::expand)
+        let mut status = ReportSink::new();
+
+        status.attempt(
+            data_type
+                .schema
+                .validate_constraints(value)
+                .change_context(TraversalError::ConstraintUnfulfilled),
+        );
+
+        if metadata.data_type_id.as_ref() == Some(&data_type.schema.id)
+            && data_type.schema.r#abstract
+        {
+            status.capture(TraversalError::AbstractDataType {
+                id: data_type.schema.id.clone(),
+            });
+        }
+
+        status.finish()
     }
 }
 
@@ -312,20 +325,20 @@ impl EntityVisitor for EntityPreprocessor {
                     });
                 }
 
-                if let Err(error) = type_provider
+                let desired_data_type = type_provider
                     .provide_type(data_type_url)
                     .await
                     .change_context_lazy(|| TraversalError::DataTypeRetrieval {
                         id: DataTypeReference {
                             url: data_type.schema.id.clone(),
                         },
-                    })?
-                    .borrow()
-                    .schema
-                    .validate_constraints(value)
-                    .change_context(TraversalError::ConstraintUnfulfilled)
+                    })?;
+
+                if let Err(error) = ValueValidator
+                    .visit_value(desired_data_type.borrow(), value, metadata, type_provider)
+                    .await
                 {
-                    status.capture(error);
+                    status.append(error);
                 }
             }
         } else {
diff --git a/libs/@local/hash-validation/src/lib.rs b/libs/@local/hash-validation/src/lib.rs
index 28b436f4ed2..4816bf807b3 100644
--- a/libs/@local/hash-validation/src/lib.rs
+++ b/libs/@local/hash-validation/src/lib.rs
@@ -1,6 +1,8 @@
 #![feature(extend_one)]
 #![feature(hash_raw_entry)]
 
+extern crate alloc;
+
 pub mod error;
 
 pub use self::entity_type::{EntityPreprocessor, EntityValidationError};
@@ -92,6 +94,7 @@ pub trait EntityProvider {
 
 #[cfg(test)]
 mod tests {
+    use alloc::sync::Arc;
     use std::collections::HashMap;
 
     use graph_types::{
@@ -150,9 +153,9 @@ mod tests {
 
     struct Provider {
         entities: HashMap<EntityId, Entity>,
-        entity_types: HashMap<VersionedUrl, ClosedEntityType>,
-        property_types: HashMap<VersionedUrl, PropertyType>,
-        data_types: HashMap<VersionedUrl, DataTypeWithMetadata>,
+        entity_types: HashMap<VersionedUrl, Arc<ClosedEntityType>>,
+        property_types: HashMap<VersionedUrl, Arc<PropertyType>>,
+        data_types: HashMap<VersionedUrl, Arc<DataTypeWithMetadata>>,
     }
     impl Provider {
         fn new(
@@ -166,14 +169,22 @@ mod tests {
                     .into_iter()
                     .map(|entity| (entity.metadata.record_id.entity_id, entity))
                     .collect(),
-                entity_types: entity_types.into_iter().collect(),
+                entity_types: entity_types
+                    .into_iter()
+                    .map(|(url, schema)| (url, Arc::new(schema)))
+                    .collect(),
                 property_types: property_types
                     .into_iter()
-                    .map(|schema| (schema.id.clone(), schema))
+                    .map(|schema| (schema.id.clone(), Arc::new(schema)))
                     .collect(),
                 data_types: data_types
                     .into_iter()
-                    .map(|schema| (schema.id.clone(), generate_data_type_metadata(schema)))
+                    .map(|schema| {
+                        (
+                            schema.id.clone(),
+                            Arc::new(generate_data_type_metadata(schema)),
+                        )
+                    })
                     .collect(),
             }
         }
@@ -232,42 +243,54 @@ mod tests {
     }
 
     impl OntologyTypeProvider<ClosedEntityType> for Provider {
+        type Value = Arc<ClosedEntityType>;
+
         #[expect(refining_impl_trait)]
         async fn provide_type(
             &self,
             type_id: &VersionedUrl,
-        ) -> Result<&ClosedEntityType, Report<InvalidEntityType>> {
-            self.entity_types.get(type_id).ok_or_else(|| {
-                Report::new(InvalidEntityType {
-                    id: type_id.clone(),
+        ) -> Result<Arc<ClosedEntityType>, Report<InvalidEntityType>> {
+            self.entity_types
+                .get(type_id)
+                .map(Arc::clone)
+                .ok_or_else(|| {
+                    Report::new(InvalidEntityType {
+                        id: type_id.clone(),
+                    })
                 })
-            })
         }
     }
 
     impl OntologyTypeProvider<PropertyType> for Provider {
+        type Value = Arc<PropertyType>;
+
         #[expect(refining_impl_trait)]
         async fn provide_type(
             &self,
             type_id: &VersionedUrl,
-        ) -> Result<&PropertyType, Report<InvalidPropertyType>> {
-            self.property_types.get(type_id).ok_or_else(|| {
-                Report::new(InvalidPropertyType {
-                    id: type_id.clone(),
+        ) -> Result<Arc<PropertyType>, Report<InvalidPropertyType>> {
+            self.property_types
+                .get(type_id)
+                .map(Arc::clone)
+                .ok_or_else(|| {
+                    Report::new(InvalidPropertyType {
+                        id: type_id.clone(),
+                    })
                 })
-            })
         }
     }
 
     impl PropertyTypeProvider for Provider {}
 
     impl OntologyTypeProvider<DataTypeWithMetadata> for Provider {
+        type Value = Arc<DataTypeWithMetadata>;
+
         #[expect(refining_impl_trait)]
         async fn provide_type(
             &self,
             type_id: &VersionedUrl,
-        ) -> Result<&DataTypeWithMetadata, Report<InvalidDataType>> {
-            self.data_types.get(type_id).ok_or_else(|| {
+        ) -> Result<Arc<DataTypeWithMetadata>, Report<InvalidDataType>> {
+            self.data_types.get(type_id).map(Arc::clone).ok_or_else(|| {
                 Report::new(InvalidDataType {
                     id: type_id.clone(),
                 })
diff --git a/tests/hash-graph-http/tests/ambiguous.http b/tests/hash-graph-http/tests/ambiguous.http
index 726fd6a44ac..4a34d01647b 100644
--- a/tests/hash-graph-http/tests/ambiguous.http
+++ b/tests/hash-graph-http/tests/ambiguous.http
@@ -49,7 +49,8 @@ X-Authenticated-User-Actor-Id: {{account_id}}
         "title": "Length",
         "type": "number",
         "description": "A unit of length",
-        "minimum": 0
+        "minimum": 0,
+        "abstract": true
       },
       {
         "$schema": "https://blockprotocol.org/types/modules/graph/0.3/schema/data-type",
diff --git a/tests/hash-graph-test-data/rust/src/data_type/boolean.json b/tests/hash-graph-test-data/rust/src/data_type/boolean.json
index 0b0dc879588..d7ae2d2c226 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/boolean.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/boolean.json
@@ -4,5 +4,6 @@
   "$id": "https://blockprotocol.org/@blockprotocol/types/data-type/boolean/v/1",
   "title": "Boolean",
   "description": "A True or False value",
-  "type": "boolean"
+  "type": "boolean",
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/centimeter_v1.json b/tests/hash-graph-test-data/rust/src/data_type/centimeter_v1.json
index 7d1e5e08974..43c9332d228 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/centimeter_v1.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/centimeter_v1.json
@@ -9,5 +9,6 @@
     {
       "$ref": "https://hash.ai/@hash/types/data-type/length/v/1"
     }
-  ]
+  ],
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/centimeter_v2.json b/tests/hash-graph-test-data/rust/src/data_type/centimeter_v2.json
index a10c846d433..3ebe56806a5 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/centimeter_v2.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/centimeter_v2.json
@@ -9,5 +9,6 @@
     {
       "$ref": "https://hash.ai/@hash/types/data-type/length/v/1"
     }
-  ]
+  ],
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/empty_list.json b/tests/hash-graph-test-data/rust/src/data_type/empty_list.json
index c2612344f1b..d6b1d26bf29 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/empty_list.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/empty_list.json
@@ -5,5 +5,6 @@
   "title": "Empty List",
   "description": "An Empty List",
   "type": "array",
-  "const": []
+  "const": [],
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/length.json b/tests/hash-graph-test-data/rust/src/data_type/length.json
index 46edf85010c..01b35f7fbe9 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/length.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/length.json
@@ -9,5 +9,6 @@
     {
       "$ref": "https://blockprotocol.org/@blockprotocol/types/data-type/number/v/1"
     }
-  ]
+  ],
+  "abstract": true
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/meter.json b/tests/hash-graph-test-data/rust/src/data_type/meter.json
index e1c6f1aa2eb..5eb30a74d86 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/meter.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/meter.json
@@ -9,5 +9,6 @@
     {
       "$ref": "https://hash.ai/@hash/types/data-type/length/v/1"
     }
-  ]
+  ],
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/null.json b/tests/hash-graph-test-data/rust/src/data_type/null.json
index 4784ffd0d38..a958b53362a 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/null.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/null.json
@@ -4,5 +4,6 @@
   "$id": "https://blockprotocol.org/@blockprotocol/types/data-type/null/v/1",
   "title": "Null",
   "description": "A placeholder value representing 'nothing'",
-  "type": "null"
+  "type": "null",
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/number.json b/tests/hash-graph-test-data/rust/src/data_type/number.json
index 3f03e57eb7c..255475d44a8 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/number.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/number.json
@@ -4,5 +4,6 @@
   "$id": "https://blockprotocol.org/@blockprotocol/types/data-type/number/v/1",
   "title": "Number",
   "description": "An arithmetical value (in the Real number system)",
-  "type": "number"
+  "type": "number",
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/object_v1.json b/tests/hash-graph-test-data/rust/src/data_type/object_v1.json
index e0b192d412b..f16381b5773 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/object_v1.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/object_v1.json
@@ -4,5 +4,6 @@
   "$id": "https://blockprotocol.org/@blockprotocol/types/data-type/object/v/1",
   "title": "Object",
   "description": "A plain JSON object with no pre-defined structure",
-  "type": "object"
+  "type": "object",
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/object_v2.json b/tests/hash-graph-test-data/rust/src/data_type/object_v2.json
index af03911bd2d..c90f27d0c95 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/object_v2.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/object_v2.json
@@ -4,5 +4,6 @@
   "$id": "https://blockprotocol.org/@blockprotocol/types/data-type/object/v/2",
   "title": "Object",
   "description": "An updated plain JSON object with no pre-defined structure",
-  "type": "object"
+  "type": "object",
+  "abstract": false
 }
diff --git a/tests/hash-graph-test-data/rust/src/data_type/text.json b/tests/hash-graph-test-data/rust/src/data_type/text.json
index 29ca3c970d2..6fda52ece87 100644
--- a/tests/hash-graph-test-data/rust/src/data_type/text.json
+++ b/tests/hash-graph-test-data/rust/src/data_type/text.json
@@ -4,5 +4,6 @@
   "$id": "https://blockprotocol.org/@blockprotocol/types/data-type/text/v/1",
   "title": "Text",
   "description": "An ordered sequence of characters",
-  "type": "string"
+  "type": "string",
+  "abstract": false
 }