diff --git a/build-tools-internal/src/integTest/groovy/org/elasticsearch/gradle/internal/transport/TransportVersionGenerationFuncTest.groovy b/build-tools-internal/src/integTest/groovy/org/elasticsearch/gradle/internal/transport/TransportVersionGenerationFuncTest.groovy
index 0f2571d7ede9d..6fedcedf8e80f 100644
--- a/build-tools-internal/src/integTest/groovy/org/elasticsearch/gradle/internal/transport/TransportVersionGenerationFuncTest.groovy
+++ b/build-tools-internal/src/integTest/groovy/org/elasticsearch/gradle/internal/transport/TransportVersionGenerationFuncTest.groovy
@@ -513,4 +513,19 @@ class TransportVersionGenerationFuncTest extends AbstractTransportVersionFuncTes
         assertGenerateAndValidateSuccess(result)
         assertUpperBound("9.2", "existing_92,8123000")
     }
+
+    def "generation cannot run on release branch"() {
+        given:
+        file("myserver/build.gradle") << """
+            tasks.named('generateTransportVersion') {
+                currentUpperBoundName = '9.1'
+            }
+        """
+
+        when:
+        def result = runGenerateTask().buildAndFail()
+
+        then:
+        assertGenerateFailure(result, "Transport version generation cannot run on release branches")
+    }
 }
diff --git a/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/GenerateTransportVersionDefinitionTask.java b/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/GenerateTransportVersionDefinitionTask.java
index 2ea758a551611..619b01168c473 100644
--- a/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/GenerateTransportVersionDefinitionTask.java
+++ b/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/GenerateTransportVersionDefinitionTask.java
@@ -96,6 +96,12 @@ public abstract class GenerateTransportVersionDefinitionTask extends DefaultTask
     @TaskAction
     public void run() throws IOException {
         TransportVersionResourcesService resources = getResourceService().get();
+        List<TransportVersionUpperBound> upstreamUpperBounds = resources.getUpperBoundsFromGitBase();
+        boolean onReleaseBranch = resources.checkIfDefinitelyOnReleaseBranch(upstreamUpperBounds, getCurrentUpperBoundName().get());
+        if (onReleaseBranch) {
+            throw new IllegalArgumentException("Transport version generation cannot run on release branches");
+        }
+
         Set<String> referencedNames = TransportVersionReference.collectNames(getReferencesFiles());
         Set<String> changedDefinitionNames = resources.getChangedReferableDefinitionNames();
         String targetDefinitionName = getTargetDefinitionName(resources, referencedNames, changedDefinitionNames);
@@ -109,7 +115,7 @@ public void run() throws IOException {
             resetAllUpperBounds(resources, idsByBase);
         } else {
             getLogger().lifecycle("Generating transport version name: " + targetDefinitionName);
-            List<TransportVersionUpperBound> upstreamUpperBounds = resources.getUpperBoundsFromGitBase();
+
             Set<String> targetUpperBoundNames = getTargetUpperBoundNames(resources, upstreamUpperBounds, targetDefinitionName);
 
             List<TransportVersionId> ids = updateUpperBounds(
diff --git a/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/TransportVersionResourcesService.java b/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/TransportVersionResourcesService.java
index e7e9a2eb566f7..41f929100825c 100644
--- a/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/TransportVersionResourcesService.java
+++ b/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/TransportVersionResourcesService.java
@@ -25,6 +25,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
@@ -259,6 +260,20 @@ private Path getUpperBoundRelativePath(String name) {
         return UPPER_BOUNDS_DIR.resolve(name + ".csv");
     }
 
+    boolean checkIfDefinitelyOnReleaseBranch(Collection<TransportVersionUpperBound> upperBounds, String currentUpperBoundName) {
+        // only want to look at definitions <= the current upper bound.
+        // TODO: we should filter all of the upper bounds/definitions that are validated by this, not just in this method
+        TransportVersionUpperBound currentUpperBound = upperBounds.stream()
+            .filter(u -> u.name().equals(currentUpperBoundName))
+            .findFirst()
+            .orElse(null);
+        if (currentUpperBound == null) {
+            // since there is no current upper bound, we don't know if we are on a release branch
+            return false;
+        }
+        return upperBounds.stream().anyMatch(u -> u.definitionId().complete() > currentUpperBound.definitionId().complete());
+    }
+
     private String getBaseRefName() {
         if (baseRefName.get() == null) {
             synchronized (baseRefName) {
diff --git a/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/ValidateTransportVersionResourcesTask.java b/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/ValidateTransportVersionResourcesTask.java
index 77dff562ca314..0cdfbd5787fd3 100644
--- a/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/ValidateTransportVersionResourcesTask.java
+++ b/build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/transport/ValidateTransportVersionResourcesTask.java
@@ -84,7 +84,7 @@ public void validateTransportVersions() throws IOException {
         Map<Integer, List<IdAndDefinition>> idsByBase = resources.getIdsByBase();
         Map<String, TransportVersionUpperBound> upperBounds = resources.getUpperBounds();
         TransportVersionUpperBound currentUpperBound = upperBounds.get(getCurrentUpperBoundName().get());
-        boolean onReleaseBranch = checkIfDefinitelyOnReleaseBranch(upperBounds);
+        boolean onReleaseBranch = resources.checkIfDefinitelyOnReleaseBranch(upperBounds.values(), getCurrentUpperBoundName().get());
         boolean validateModifications = onReleaseBranch == false || getCI().get();
 
         for (var definition : referableDefinitions.values()) {
@@ -330,15 +330,6 @@ private void validatePrimaryIds(
         );
     }
 
-    private boolean checkIfDefinitelyOnReleaseBranch(Map<String, TransportVersionUpperBound> upperBounds) {
-        // only want to look at definitions <= the current upper bound.
-        // TODO: we should filter all of the upper bounds/definitions that are validated by this, not just in this method
-        String currentUpperBoundName = getCurrentUpperBoundName().get();
-        TransportVersionUpperBound currentUpperBound = upperBounds.get(currentUpperBoundName);
-
-        return upperBounds.values().stream().anyMatch(u -> u.definitionId().complete() > currentUpperBound.definitionId().complete());
-    }
-
     private void throwDefinitionFailure(TransportVersionDefinition definition, String message) {
         Path relativePath = getResources().get().getDefinitionPath(definition);
         throw new VerificationException("Transport version definition file [" + relativePath + "] " + message);