This is not a direct alternative to ElasticSearch. Tantivy is closer to an alternative to ElasticSearch since ES is built on top of Lucene. An alternative could be achieved if built on top of Tantivy.
Sonic here only returns document identifiers so you will never be able to get document information back. This is very useful though if all you want to do is index text data and then get the stored information from another data store.
Quickwit is a search engine built on top of Tantivy (by the author of Tantivy): https://github.com/quickwit-oss/quickwit
Quickwit supports Elasticsearch compatible bulk indexing API.