OpenSearch is an open-source fork of
Elasticsearch, licensed under the permissive
Apache 2.0 license and governed by the OpenSearch Software Foundation (Linux Foundation).
"Elasticsearch B.V.", the company that developed Elasticsearch, originally developed it as Apache 2.0 open source. In 2021, the company moved Elasticsearch to more restrictive source-available licenses (SSPL and the Elastic License v2). Because of that, Amazon and the community created OpenSearch, a fork of the last Apache 2.0 Elasticsearch version.
Elasticsearch later returned to open source under the AGPLv3 license in 2024. OpenSearch keeps the permissive Apache 2.0 license, and it has its own development team, updates, and new features.