FINALLY!!!! After many delays and much fanfare, Oracle AI Database 26ai (23.26.1.0.0) has been officially released for Linux x86-64 (on-prem)!
You can find the download at oracle.com (*.zip and *.rpm)
https://www.oracle.com/database/technologies/oracle-database-software-downloads.html#db_ee
You can also find it at e-delivery.oracle.com (if you’re looking for the more “official” version).

Special note for E-Business Suite customers: While the EBS ATG group HAS announced certification of E-Business Suite R12.2 against 26ai for Exadata (which is, for many purposes just Linux x86-64), they haven’t officially announced certification for EBS R12.2 + RDBMS 26ai for on-prem Linux. Given that the two are extremely close, I would expect an announcement from them soon(ish).
https://blogs.oracle.com/ebstech/ebs-12-2-certified-with-database-release-update-23-26-on-premises-exadata