# Problem with upgrading to 9.0.0, index compability

**URL:** <https://discuss.elastic.co/t/problem-with-upgrading-to-9-0-0-index-compability/377614>\
**Category:** Elasticsearch\
**Created:** [April 29, 2025, 12:15pm UTC](https://discuss.elastic.co/t/problem-with-upgrading-to-9-0-0-index-compability/377614 "2025-04-29T12:15:49Z")\
**Posts on this page:** 1\
**Showing post:** 15

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**Author:** ![RainTown](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/raintown/32/140206_2.png) [@RainTown](https://discuss.elastic.co/u/RainTown)\
**Post date:** [December 1, 2025, 10:22am UTC](https://discuss.elastic.co/t/problem-with-upgrading-to-9-0-0-index-compability/377614/15 "2025-12-01T10:22:57Z")

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similar topic was covered in [this](https://discuss.elastic.co/t/cluster-will-not-start-after-upgrade-from-8-x-to-9-x/383690) thread

Are you 100% sure you have migrated or re-indexed all indices from 7.x or earlier? As was discussed in the thread, its easy-ish to miss things the Upgrade Assistant is telling you need done.

In the above thread there’s a long one liner that will show you the ES version the index was created with, for all indices.

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_[View the full topic](https://discuss.elastic.co/t/problem-with-upgrading-to-9-0-0-index-compability/377614)._