diff --git a/CHANGELOG.md b/CHANGELOG.md
index cf1600677..30c4bc1c6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Removed
 
 ### Fixed
+- Fixed deserialization failure when OpenSearch returns shard failures without the `primary` field in error responses by upgrading version of `opensearch-api-specification`
 
 ### Security
 
diff --git a/java-client/src/test/java/org/opensearch/client/opensearch/_types/ShardFailureTest.java b/java-client/src/test/java/org/opensearch/client/opensearch/_types/ShardFailureTest.java
new file mode 100644
index 000000000..adf059828
--- /dev/null
+++ b/java-client/src/test/java/org/opensearch/client/opensearch/_types/ShardFailureTest.java
@@ -0,0 +1,109 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.client.opensearch._types;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import jakarta.json.stream.JsonParser;
+import java.io.StringReader;
+import org.junit.Test;
+import org.opensearch.client.json.JsonpMapper;
+import org.opensearch.client.json.jackson.JacksonJsonpMapper;
+
+public class ShardFailureTest {
+
+    private final JsonpMapper mapper = new JacksonJsonpMapper();
+
+    @Test
+    public void testShardFailureWithPrimaryField() {
+        String json = "{"
+            + "\"shard\": 0,"
+            + "\"index\": \"test-index\","
+            + "\"node\": \"node-123\","
+            + "\"primary\": true,"
+            + "\"reason\": {"
+            + "  \"type\": \"query_shard_exception\","
+            + "  \"reason\": \"Failed to parse query\""
+            + "}"
+            + "}";
+
+        JsonParser parser = mapper.jsonProvider().createParser(new StringReader(json));
+        ShardFailure shardFailure = ShardFailure._DESERIALIZER.deserialize(parser, mapper);
+
+        assertNotNull(shardFailure);
+        assertEquals(0, shardFailure.shard());
+        assertEquals("test-index", shardFailure.index());
+        assertEquals("node-123", shardFailure.node());
+        assertNotNull(shardFailure.primary());
+        assertTrue(shardFailure.primary());
+        assertNotNull(shardFailure.reason());
+        assertEquals("query_shard_exception", shardFailure.reason().type());
+    }
+
+    @Test
+    public void testShardFailureWithoutPrimaryField() {
+        // This is the real-world case that fails - OpenSearch often omits the "primary" field
+        String json = "{"
+            + "\"shard\": 0,"
+            + "\"index\": \"cases-p360\","
+            + "\"node\": \"h88XL3ygSy2OxP0Ak-YIdA\","
+            + "\"reason\": {"
+            + "  \"type\": \"query_shard_exception\","
+            + "  \"reason\": \"Failed to execute query\""
+            + "}"
+            + "}";
+
+        JsonParser parser = mapper.jsonProvider().createParser(new StringReader(json));
+        ShardFailure shardFailure = ShardFailure._DESERIALIZER.deserialize(parser, mapper);
+
+        assertNotNull(shardFailure);
+        assertEquals(0, shardFailure.shard());
+        assertEquals("cases-p360", shardFailure.index());
+        assertEquals("h88XL3ygSy2OxP0Ak-YIdA", shardFailure.node());
+        // Primary field should be null when not present in JSON
+        assertNull(shardFailure.primary());
+        assertNotNull(shardFailure.reason());
+        assertEquals("query_shard_exception", shardFailure.reason().type());
+    }
+
+    @Test
+    public void testErrorCauseWithFailedShards() {
+        // Test a more complete error response with failed_shards array
+        // This verifies that ErrorCause can be deserialized when it contains
+        // a failed_shards array with ShardFailure objects missing the primary field
+        String json = "{"
+            + "\"type\": \"search_phase_execution_exception\","
+            + "\"reason\": \"all shards failed\","
+            + "\"metadata\": {"
+            + "  \"failed_shards\": ["
+            + "    {"
+            + "      \"shard\": 0,"
+            + "      \"index\": \"test-index\","
+            + "      \"node\": \"node-1\","
+            + "      \"reason\": {"
+            + "        \"type\": \"query_shard_exception\","
+            + "        \"reason\": \"Parse error\""
+            + "      }"
+            + "    }"
+            + "  ]"
+            + "}"
+            + "}";
+
+        JsonParser parser = mapper.jsonProvider().createParser(new StringReader(json));
+        ErrorCause errorCause = ErrorCause._DESERIALIZER.deserialize(parser, mapper);
+
+        // The main goal is to verify deserialization succeeds without throwing
+        assertNotNull(errorCause);
+        assertEquals("search_phase_execution_exception", errorCause.type());
+        assertEquals("all shards failed", errorCause.reason());
+    }
+}