diff --git a/compatibility-tests/sdk-test-java/src/test/java/com/floci/test/Ec2Tests.java b/compatibility-tests/sdk-test-java/src/test/java/com/floci/test/Ec2Tests.java
index eb3e7fd62c..14a19c755a 100644
--- a/compatibility-tests/sdk-test-java/src/test/java/com/floci/test/Ec2Tests.java
+++ b/compatibility-tests/sdk-test-java/src/test/java/com/floci/test/Ec2Tests.java
@@ -278,6 +278,22 @@ void describeInstanceTypeProcessorArchitectures() {
                 .containsExactly("arm64");
     }
 
+    /** Regression coverage for the Karpenter instance-type compatibility contract. */
+    @Test
+    @Order(7)
+    @DisplayName("DescribeInstanceTypes - supported usage classes")
+    void describeInstanceTypeSupportedUsageClasses() {
+        DescribeInstanceTypesResponse resp = ec2.describeInstanceTypes(DescribeInstanceTypesRequest.builder()
+                .instanceTypes(InstanceType.M5_LARGE, InstanceType.fromValue("t4g.medium"),
+                        InstanceType.fromValue("m6gd.large"))
+                .build());
+
+        assertThat(resp.instanceTypes()).hasSize(3);
+        assertThat(resp.instanceTypes()).allSatisfy(instanceType ->
+                assertThat(instanceType.supportedUsageClassesAsStrings())
+                        .containsExactlyInAnyOrder("on-demand", "spot"));
+    }
+
     @Test
     @Order(7)
     @DisplayName("CreateFleet - dry-run and instant on-demand launch")
diff --git a/src/main/java/io/github/hectorvent/floci/services/ec2/Ec2InstanceTypeCatalog.java b/src/main/java/io/github/hectorvent/floci/services/ec2/Ec2InstanceTypeCatalog.java
index eaffb4c492..b281e0f28c 100644
--- a/src/main/java/io/github/hectorvent/floci/services/ec2/Ec2InstanceTypeCatalog.java
+++ b/src/main/java/io/github/hectorvent/floci/services/ec2/Ec2InstanceTypeCatalog.java
@@ -95,6 +95,9 @@ private static Map<String, CatalogInstanceType> indexInstanceTypes(List<CatalogI
             if (instanceType.supportedArchitectures == null || instanceType.supportedArchitectures.isEmpty()) {
                 throw new IllegalStateException("EC2 instance type catalog entry is missing supportedArchitectures: " + name);
             }
+            if (instanceType.supportedUsageClasses == null || instanceType.supportedUsageClasses.isEmpty()) {
+                throw new IllegalStateException("EC2 instance type catalog entry is missing supportedUsageClasses: " + name);
+            }
             if (instanceType.encryptionInTransitSupported == null) {
                 throw new IllegalStateException(
                         "EC2 instance type catalog entry is missing encryptionInTransitSupported: " + name);
@@ -156,6 +159,7 @@ public static final class CatalogInstanceType {
         public int memoryMib;
         public int localStorageGiB;
         public List<String> supportedArchitectures = List.of();
+        public List<String> supportedUsageClasses = List.of("on-demand", "spot");
         public Boolean currentGeneration;
         public Boolean encryptionInTransitSupported;
         public Integer defaultNetworkCardIndex;
@@ -170,6 +174,7 @@ public Map<String, Object> toResponseMap() {
             type.put("instanceStorageSupported", localStorageGiB > 0);
             type.put("localStorageGiB", localStorageGiB);
             type.put("supportedArchitectures", List.copyOf(supportedArchitectures));
+            type.put("supportedUsageClasses", List.copyOf(supportedUsageClasses));
             type.put("currentGeneration", currentGeneration == null || currentGeneration);
             Map<String, Object> networkInfo = new LinkedHashMap<>();
             networkInfo.put("encryptionInTransitSupported", encryptionInTransitSupported);
diff --git a/src/main/java/io/github/hectorvent/floci/services/ec2/Ec2QueryHandler.java b/src/main/java/io/github/hectorvent/floci/services/ec2/Ec2QueryHandler.java
index 793a3de2d7..bb55b895d4 100644
--- a/src/main/java/io/github/hectorvent/floci/services/ec2/Ec2QueryHandler.java
+++ b/src/main/java/io/github/hectorvent/floci/services/ec2/Ec2QueryHandler.java
@@ -3849,7 +3849,12 @@ private Response handleDescribeInstanceTypes(MultivaluedMap<String, String> p, S
             for (String arch : (List<String>) t.get("supportedArchitectures")) {
                 xml.elem("item", arch);
             }
-            xml.end("supportedArchitectures").end("processorInfo");
+            xml.end("supportedArchitectures").end("processorInfo")
+                    .start("supportedUsageClasses");
+            for (String usageClass : (List<String>) t.get("supportedUsageClasses")) {
+                xml.elem("item", usageClass);
+            }
+            xml.end("supportedUsageClasses");
             Map<String, Object> networkInfo = (Map<String, Object>) t.get("networkInfo");
             xml.start("networkInfo")
                     .elem("encryptionInTransitSupported",
diff --git a/src/test/java/io/github/hectorvent/floci/services/stepfunctions/AslExecutorFailStateErrorCauseTest.java b/src/test/java/io/github/hectorvent/floci/services/stepfunctions/AslExecutorFailStateErrorCauseTest.java
index 00743015ee..aedb5ae7d8 100644
--- a/src/test/java/io/github/hectorvent/floci/services/stepfunctions/AslExecutorFailStateErrorCauseTest.java
+++ b/src/test/java/io/github/hectorvent/floci/services/stepfunctions/AslExecutorFailStateErrorCauseTest.java
@@ -31,6 +31,9 @@
  * <p>Both fields are resolved through the same reference-path resolver a {@code ".$"} payload
  * template field uses, so an unresolvable path fails with {@code States.Runtime}, matching the
  * precedent set for issue #2521 in {@link AslExecutorUnresolvableJsonPathTest}.
+ *
+ * <p>The fixture supplies all service handlers required by the production executor, including
+ * the SNS handler introduced by the Step Functions SNS integration.
  */
 @QuarkusTest
 class AslExecutorFailStateErrorCauseTest {