[2023] SISI for Content Creators and EVE partners only now?

There is a Statement from the Developers in this Thread:

Connection Failed ‘The cluster is not accepting connections’ - EVE Technology and Research Center / Test Server Feedback - EVE Online Forums

Just to add additional clarity - content creators and EVE Partners had access to Singularity the weekend before EVE Viridian launched but then lost access on Tuesday, June 13th.

Hi everyone,

We just wanted to advise you that the Singularity test server will continue to be inaccessible to players throughout July and August unless needed to test a specific feature or perform a mass test.

We’ll provide a further update as we approach September.