I think only for those editors. Google does also give a free API Key (aistudio.google.com) for the underlying models (though not the coding fine-tuned one) But IMO the free tier is rate limited a bit too much to build your own extension out of it for free.
(Zero analogies to drug dealers. Wink wink.)
So can this be used standalone or must you use JetBrains / VSCode / Firebase / GitHub with no other option? I am not seeing any.