This landed as available via string resolution at unique-id but did not come with a public import, meaning it doesn't currently work in <template>/strict mode. Per discussion at the Framework team meeting a few weeks ago, it should be exported from @ember/helper, the same as the other public helpers which are not built-ins (hash, array, concat, get, and fn etc.).

It needs two things to be public:

• Create public import for uniqueId helper #20171
• A note in the blog post for that release (which should be 4.8).

Additionally, we'll want to update ecosystem support for it:

• add it to the list of allowed built-ins for the no-curly-component-invocation rule in ember-template-lint
  • Usage of unique-id helper causes rule triggers ember-template-lint/ember-template-lint#2592
  • Add unique-id to allowed built-in helpers in no-curly-component-invocation and no-implicit-this rules ember-template-lint/ember-template-lint#2593