# Data stream compatibility issues upgrading from 8.18 to 9

**URL:** <https://discuss.elastic.co/t/data-stream-compatibility-issues-upgrading-from-8-18-to-9/378652>\
**Category:** Elasticsearch\
**Created:** [May 28, 2025, 1:51pm UTC](https://discuss.elastic.co/t/data-stream-compatibility-issues-upgrading-from-8-18-to-9/378652 "2025-05-28T13:51:22Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![mcflynnthm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/mcflynnthm/32/143395_2.png) [@mcflynnthm](https://discuss.elastic.co/u/mcflynnthm)\
**Post date:** [May 28, 2025, 1:51pm UTC](https://discuss.elastic.co/t/data-stream-compatibility-issues-upgrading-from-8-18-to-9/378652/1 "2025-05-28T13:51:22Z")

</div>

Testing the upgrade of my cluster from 8.18 to 9.0, the Upgrade Assistant reports it cannot retrieve deprecation issues for Elasticsearch. Checked _/\_migration/deprecations_ and among other things, get the following:

```auto
"data_streams": {
    ".items-default": [
      {
        "level": "critical",
        "message": "Old data stream with a compatibility version < 8.0",
        "url": "https://www.elastic.co/guide/en/elasticsearch/reference/current/migrating-8.0.html#breaking-changes-8.0",
        "details": "This data stream has backing indices that were created before Elasticsearch 8.0.0",
        "resolve_during_rolling_upgrade": false,
        "_meta": {
          "total_backing_indices": 1,
          "indices_requiring_upgrade_count": 1,
          "indices_requiring_upgrade": [
            ".items-default-000001"
          ],
          "reindex_required": true
        }
      }
    ],
    ".lists-default": [
      {
        "level": "critical",
        "message": "Old data stream with a compatibility version < 8.0",
        "url": "https://www.elastic.co/guide/en/elasticsearch/reference/current/migrating-8.0.html#breaking-changes-8.0",
        "details": "This data stream has backing indices that were created before Elasticsearch 8.0.0",
        "resolve_during_rolling_upgrade": false,
        "_meta": {
          "total_backing_indices": 1,
          "indices_requiring_upgrade_count": 1,
          "indices_requiring_upgrade": [
            ".lists-default-000001"
          ],
          "reindex_required": true
        }
      }
    ]

```

I attempted to use _/\_reindex_ on both the identified indices, and it didn't throw any errors but still didn't resolve the issue. I'm sure I'm missing something obvious, but I'm not sure how to proceed with these.

---

<div class="post-metadata">

**Author:** ![mcflynnthm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/mcflynnthm/32/143395_2.png) [@mcflynnthm](https://discuss.elastic.co/u/mcflynnthm)\
**Post date:** [May 28, 2025, 7:06pm UTC](https://discuss.elastic.co/t/data-stream-compatibility-issues-upgrading-from-8-18-to-9/378652/2 "2025-05-28T19:06:58Z")

</div>

OK, I solved my own issue. I had to use

```auto
POST /_migration/reindex
{
    "source": {
        "index": "[data-stream]"
    },
    "mode":"upgrade"
}

```

for each flagged data stream.

Still other deprecation issues to resolve, but just updating/closing this.