The full quote adds some important context to what they meant by “unique”.

Today at the Cannes Lions International Festival of Creativity, we announced that the Threads API is now available to all developers. We believe it will enable creators, developers and brands to build their own unique integrations, manage their Threads presence at scale, and easily share inspiring content with their communities.

These “unique integrations” aren’t features or plugins exclusive to Threads in comparison to the larger fediverse, they’re the types of features that would be unique to the applications developers who use the API will create, but aren’t available in the default Threads app. For example, one app’s “unique” feature might be collating data on interactions with your posts (like to track brand growth), while another’s might be built for scheduled or automated posting (like a streamer who sends out automatic Tweets when they go live on Twitch).

These sorts of things are all available currently through Mastodon’s API, Threads is playing catch-up here.