Ask HN: Contact form spam despite trying everything

I'm at my wit's end with contact form spam on my sites. I've tried:

CleanTalk - caught some spam but still getting through, plus the monthly cost adds up Turnstile - better UX than reCAPTCHA but bots seem to be solving it reCAPTCHA v2 - effective but users hate the image challenges reCAPTCHA v3 - invisible but I'm still getting 20-30 spam submissions daily even with strict thresholds

I've also implemented honeypots, rate limiting, basic keyword filtering, and email validation (both format checking and MX record verification). The spam is getting more sophisticated - proper English, realistic email addresses that actually exist, even passing behavioral checks. What I'm curious about: How does Hacker News handle spam so effectively? I rarely see spam comments here, and there's no visible CAPTCHA. Are you using something custom, or is there a service/approach I'm missing? For context, I get about 500 legitimate form submissions per month, so I need something that won't block real users while stopping the bot flood. What's worked best for your sites? Especially interested in hearing from anyone who's dealt with determined, human-like spam at scale.