Actually, Gemini 2.0 Flash is available for free, just as long as you aren’t of course sending a million requests to it each day. It’s working fine for my forum right now with zero cost, and it is defenitely more precise and “smarter” than Akismet.
However, if the AI Spam detection plan fails, I still have the Akismet plugin installed on my site and ready to go if I ever need it again, and I think you can still install it. (Since it is being deprecated though, I don’t expect it to stick around forever). Also remember that trust levels are a fundamental core of Discourse that help you manage spam on your site. 