diff --git a/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/CoreDatatype.java b/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/CoreDatatype.java
index 7ed0df4fa90..19db1269cea 100644
--- a/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/CoreDatatype.java
+++ b/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/CoreDatatype.java
@@ -110,7 +110,7 @@ enum XSD implements CoreDatatype {
 		public static final String NAMESPACE = "http://www.w3.org/2001/XMLSchema#";
 
 		private static IRI iri(String localName) {
-			return new CoreDatatypeHelper.DatatypeIRI(NAMESPACE, localName);
+			return new InternedIRI(NAMESPACE, localName);
 		}
 
 		private final IRI iri;
@@ -275,7 +275,7 @@ enum RDF implements CoreDatatype {
 		public static final String NAMESPACE = "http://www.w3.org/1999/02/22-rdf-syntax-ns#";
 
 		private static IRI iri(String localName) {
-			return new CoreDatatypeHelper.DatatypeIRI(NAMESPACE, localName);
+			return new InternedIRI(NAMESPACE, localName);
 		}
 
 		private final IRI iri;
@@ -316,7 +316,7 @@ enum GEO implements CoreDatatype {
 		public static final String NAMESPACE = "http://www.opengis.net/ont/geosparql#";
 
 		private static IRI iri(String localName) {
-			return new CoreDatatypeHelper.DatatypeIRI(NAMESPACE, localName);
+			return new InternedIRI(NAMESPACE, localName);
 		}
 
 		private final IRI iri;
diff --git a/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/CoreDatatypeHelper.java b/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/CoreDatatypeHelper.java
index 100e61264e2..6455f6707af 100644
--- a/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/CoreDatatypeHelper.java
+++ b/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/CoreDatatypeHelper.java
@@ -43,38 +43,4 @@ static Map<IRI, CoreDatatype> getReverseLookup() {
 		return reverseLookup;
 	}
 
-	static class DatatypeIRI extends AbstractIRI {
-
-		private static final long serialVersionUID = 169243624049169159L;
-
-		private final String namespace;
-		private final String localName;
-		private final String stringValue;
-
-		public DatatypeIRI(String namespace, String localName) {
-			this.namespace = namespace;
-			this.localName = localName;
-			this.stringValue = namespace.concat(localName).intern();
-		}
-
-		@Override
-		public String stringValue() {
-			return stringValue;
-		}
-
-		@Override
-		public String getNamespace() {
-			return namespace;
-		}
-
-		@Override
-		public String getLocalName() {
-			return localName;
-		}
-
-		@Override
-		public String toString() {
-			return stringValue;
-		}
-	}
 }
diff --git a/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/InternedIRI.java b/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/InternedIRI.java
new file mode 100644
index 00000000000..f75d2ad101a
--- /dev/null
+++ b/core/model-api/src/main/java/org/eclipse/rdf4j/model/base/InternedIRI.java
@@ -0,0 +1,131 @@
+/*******************************************************************************
+ * Copyright (c) 2022 Eclipse RDF4J contributors.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Distribution License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ ******************************************************************************/
+
+package org.eclipse.rdf4j.model.base;
+
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.lang.reflect.Field;
+
+import org.eclipse.rdf4j.common.annotation.InternalUseOnly;
+import org.eclipse.rdf4j.model.IRI;
+import org.eclipse.rdf4j.model.Value;
+
+/**
+ * An IRI implementation that interns the stringValue so that two objects can be compared by their stringValue
+ * reference. Must only be used for IRIs that are effectively ´public static final´ and only for a very limited number
+ * of objects because string interning affects the GC root set
+ * (https://shipilev.net/jvm/anatomy-quarks/10-string-intern/).
+ *
+ */
+@InternalUseOnly
+public final class InternedIRI implements IRI {
+	private static final long serialVersionUID = 169243429049169159L;
+
+	private final String namespace;
+	private final String localName;
+	private final String stringValue;
+	private final int hashCode;
+
+	public InternedIRI(String namespace, String localName) {
+		this.namespace = namespace;
+		this.localName = localName;
+		this.stringValue = namespace.concat(localName).intern();
+		this.hashCode = stringValue.hashCode();
+	}
+
+	@Override
+	public String stringValue() {
+		return stringValue;
+	}
+
+	@Override
+	public String getNamespace() {
+		return namespace;
+	}
+
+	@Override
+	public String getLocalName() {
+		return localName;
+	}
+
+	@Override
+	public String toString() {
+		return stringValue;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o) {
+			return true;
+		}
+
+		if (o instanceof InternedIRI) {
+			// Because the stringValue is interned we can simply compare the reference.
+			return stringValue == ((InternedIRI) o).stringValue;
+		}
+
+		if (o instanceof Value) {
+			Value value = (Value) o;
+			if (value.isIRI()) {
+				return stringValue.equals(value.stringValue());
+			}
+		}
+
+		return false;
+	}
+
+	@Override
+	public int hashCode() {
+		return hashCode;
+	}
+
+	private void writeObject(ObjectOutputStream out) throws IOException {
+		out.writeInt(hashCode);
+		out.writeUTF(namespace);
+		out.writeUTF(localName);
+	}
+
+	private void readObject(ObjectInputStream in) throws ClassNotFoundException, IOException {
+		int hashCode = in.readInt();
+		String namespace = in.readUTF();
+		String localName = in.readUTF();
+
+		// Deserialization in Java typically uses Unsafe to set final fields, we need to use reflection.
+		writeToPrivateFinalField(namespace, "namespace");
+		writeToPrivateFinalField(localName, "localName");
+		writeToPrivateFinalField(hashCode, "hashCode");
+
+		// The main reason we need a custom deserialization is that we need to intern the stringValue field.
+		String stringValue = (namespace + localName).intern();
+		writeToPrivateFinalField(stringValue, "stringValue");
+		assert stringValue.hashCode() == hashCode;
+	}
+
+	private void writeToPrivateFinalField(String value, String fieldName) {
+		try {
+			Field field = InternedIRI.class.getDeclaredField(fieldName);
+			field.setAccessible(true);
+			field.set(this, value);
+		} catch (NoSuchFieldException | IllegalAccessException e) {
+			throw new RuntimeException(e);
+		}
+	}
+
+	private void writeToPrivateFinalField(int value, String fieldName) {
+		try {
+			Field field = InternedIRI.class.getDeclaredField(fieldName);
+			field.setAccessible(true);
+			field.set(this, value);
+		} catch (NoSuchFieldException | IllegalAccessException e) {
+			throw new RuntimeException(e);
+		}
+	}
+
+}
diff --git a/core/model-vocabulary/src/main/java/org/eclipse/rdf4j/model/vocabulary/Vocabularies.java b/core/model-vocabulary/src/main/java/org/eclipse/rdf4j/model/vocabulary/Vocabularies.java
index b4469c1d25b..1e21780c6ec 100644
--- a/core/model-vocabulary/src/main/java/org/eclipse/rdf4j/model/vocabulary/Vocabularies.java
+++ b/core/model-vocabulary/src/main/java/org/eclipse/rdf4j/model/vocabulary/Vocabularies.java
@@ -8,67 +8,57 @@
 
 package org.eclipse.rdf4j.model.vocabulary;
 
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.lang.reflect.Field;
+
 import org.eclipse.rdf4j.model.IRI;
 import org.eclipse.rdf4j.model.Namespace;
-import org.eclipse.rdf4j.model.base.AbstractIRI;
+import org.eclipse.rdf4j.model.Value;
 import org.eclipse.rdf4j.model.base.AbstractNamespace;
+import org.eclipse.rdf4j.model.base.InternedIRI;
 
 /**
  * Utility methods related to RDF vocabularies.
  *
  * @author Alessandro Bollini
- * @since 3.5.0
- *
  * @implNote To be eventually removed or merged with {@code org.eclipse.rdf4j.model.util.Vocabularies}.
+ * @since 3.5.0
  */
 class Vocabularies {
 
-	static Namespace createNamespace(String prefix, String namespace) {
-		return new AbstractNamespace() {
-
-			private static final long serialVersionUID = 3913851292983866831L;
-
-			@Override
-			public String getPrefix() {
-				return prefix;
-			}
-
-			@Override
-			public String getName() {
-				return namespace;
-			}
-
-		};
+	private Vocabularies() {
 	}
 
-	static IRI createIRI(String namespace, String localName) {
-		return new AbstractIRI() {
-
-			private static final long serialVersionUID = 1692436252019169159L;
+	static Namespace createNamespace(String prefix, String namespace) {
+		return new VocabularyNamespace(prefix, namespace);
+	}
 
-			// ;( removing .toString() causes a 2x penalty in .equals() performance on Oracle JDK 1.8/11…
+	private static class VocabularyNamespace extends AbstractNamespace {
 
-			private final String stringValue = (namespace + localName).toString();
+		private final String prefix;
+		private final String namespace;
 
-			@Override
-			public String stringValue() {
-				return stringValue;
-			}
+		public VocabularyNamespace(String prefix, String namespace) {
 
-			@Override
-			public String getNamespace() {
-				return namespace;
-			}
+			this.prefix = prefix;
+			this.namespace = namespace;
+		}
 
-			@Override
-			public String getLocalName() {
-				return localName;
-			}
+		@Override
+		public String getPrefix() {
+			return prefix;
+		}
 
-		};
+		@Override
+		public String getName() {
+			return namespace;
+		}
 	}
 
-	private Vocabularies() {
+	static IRI createIRI(String namespace, String localName) {
+		return new InternedIRI(namespace, localName);
 	}
 
 }