This meta issue tracks the various changes relating to offering a "case insensitive" option to various term-level queries (term, terms, prefix, wildcard, regex) at search time. It replaces the previous #53603 which meandered with various discussions.
In query DSL we will offer a new case_insensitive flag which can only be set to true to enable new behaviour. When left unset the existing behaviour is used (which is inconsistent - keyword fields with normalizers normalize query terms while text fields do not). Due to these inconsistencies and lack of guarantees, setting the case_insensitive flag to false will throw an error.

Tasks

• Add case insensitive option to Lucene's RegExpQuery - merged RegExp - add case insensitive matching option apache/lucene-solr#1541
• regexp queries in elasticsearch DSL - Issue PR Search - add case insensitive support for regex queries. #59441
• Lucene query_string support for /Foo/i regex syntax - PR LUCENE-9445 Add support for case insensitive regex searches in QueryParser apache/lucene-solr#1708
• term queries in elasticsearch DSL- issue Search - add case insensitive flag to term, prefix and wildcard queries #61546
• terms queries in elasticsearch DSL
• prefix queries in elasticsearch DSL - issue Search - add case insensitive flag to term, prefix and wildcard queries #61546
• wildcard query in elasticsearch DSL - issue Search - add case insensitive flag to term, prefix and wildcard queries #61546