Kagi has FastGPT and the AI assistant mode (available via several bangs like !fast, !expert, and !code). Though the latter is beta and only available to Ultimate subscribers
When I ask an AI tricky questions, the responses usually point me in the right direction without fully solving the problem, so those citation links are really useful.
With Bard in particular, I find it often gives a confident but incorrect answer. When I point this out, it apologises then gives another incorrect answer, and so on.