The knowledge sources do not mention any specific or official sunset/end-of-support date for Legacy ID Management.
They do state that Legacy ID Management still exists and is documented separately, and that you must create a new project to move to Original or Simplified ID Merge; there is no automatic conversion. [Deciding to migrate]
Because no concrete deprecation timeline is provided in these docs, I can’t say when (or if) Legacy ID Management will be fully turned off. For an up‑to‑date answer, the docs recommend contacting Mixpanel Support for migration and plan questions. [Identity FAQ]
