diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9cfcd4e6dfbd1..89616a8977e5a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Support prefix list for remote repository attributes([#16271](https://github.com/opensearch-project/OpenSearch/pull/16271))
 - Add new configuration setting `synonym_analyzer`, to the `synonym` and `synonym_graph` filters, enabling the specification of a custom analyzer for reading the synonym file ([#16488](https://github.com/opensearch-project/OpenSearch/pull/16488)).
 - Add stats for remote publication failure and move download failure stats to remote methods([#16682](https://github.com/opensearch-project/OpenSearch/pull/16682/))
+- Make timezone optional for strict_date_time format ([#16701](https://github.com/opensearch-project/OpenSearch/pull/16701))
 
 ### Dependencies
 - Bump `com.google.cloud:google-cloud-core-http` from 2.23.0 to 2.47.0 ([#16504](https://github.com/opensearch-project/OpenSearch/pull/16504))
diff --git a/server/src/main/java/org/opensearch/common/time/DateFormatters.java b/server/src/main/java/org/opensearch/common/time/DateFormatters.java
index 527dce7677dd8..f84d8a31decd7 100644
--- a/server/src/main/java/org/opensearch/common/time/DateFormatters.java
+++ b/server/src/main/java/org/opensearch/common/time/DateFormatters.java
@@ -732,6 +732,8 @@ public class DateFormatters {
     /*
      * Returns a formatter that combines a full date and time, separated by a 'T'
      * (uuuu-MM-dd'T'HH:mm:ss.SSSZZ).
+     * Timezone is optional and defaults to UTC,
+     * as Python's isoformat() can outputs ISO 8601-compliant dates that lack a timezone.
      */
     private static final DateFormatter STRICT_DATE_TIME = new JavaDateFormatter(
         "strict_date_time",
@@ -741,7 +743,9 @@ public class DateFormatters {
             .toFormatter(Locale.ROOT)
             .withResolverStyle(ResolverStyle.STRICT),
         new DateTimeFormatterBuilder().append(STRICT_DATE_FORMATTER)
+            .optionalStart()
             .append(TIME_ZONE_FORMATTER_NO_COLON)
+            .optionalEnd()
             .toFormatter(Locale.ROOT)
             .withResolverStyle(ResolverStyle.STRICT)
     );
diff --git a/server/src/test/java/org/opensearch/common/time/DateFormattersTests.java b/server/src/test/java/org/opensearch/common/time/DateFormattersTests.java
index 2ccee197686ec..bb69ebd6c16c3 100644
--- a/server/src/test/java/org/opensearch/common/time/DateFormattersTests.java
+++ b/server/src/test/java/org/opensearch/common/time/DateFormattersTests.java
@@ -828,6 +828,22 @@ public void testCamelCaseDeprecation() {
         }
     }
 
+    public void testStrictDateTimeDefaultsToUTC() {
+        DateFormatter dateFormatter = DateFormatter.forPattern("strict_date_time");
+        // "strict_date_time" formatter should be able to parse with and without a timezone specified, as both are valid in ISO 8601
+        // See https://github.com/opensearch-project/OpenSearch/issues/16673
+        assertEquals(
+            ZonedDateTime.of(2024, 11, 21, 0, 0, 0, 0, ZoneOffset.UTC),
+            DateFormatters.from(dateFormatter.parse("2024-11-21T00:00:00Z"))
+        );
+
+        // Should default to UTC without a timezone specified
+        assertEquals(
+            ZonedDateTime.of(2024, 11, 21, 0, 0, 0, 0, ZoneOffset.UTC),
+            DateFormatters.from(dateFormatter.parse("2024-11-21T00:00:00"))
+        );
+    }
+
     void assertDateTimeEquals(String toTest, DateFormatter candidateParser, DateFormatter baselineParser) {
         Instant gotInstant = DateFormatters.from(candidateParser.parse(toTest)).toInstant();
         Instant expectedInstant = DateFormatters.from(baselineParser.parse(toTest)).toInstant();