Most times cats and rabbits are fine together without too much intro needed. Whether you trust them free-roam unsupervised will depend on their personalities. Are your bunnies very small or skittish? Does the cat have a strong prey drive? Usually we only worry when the bunnies are babies or very small, and the cat has a strong prey drive.
Really you just need to supervise them at first to make sure your cat isn’t harassing the bun. If the buns are bold and the cat is timid, you might even need to worry about the bunnies bullying the cat!
With my cat, I’m sure to only get him toys that do not mimic rabbits (so none of those big “grab and kick” toys), and I play with him during the times he gets frisky. I’m had some bunnies that get spooked by him so I have to supervise them more closely, but my current bunnies pretty much ignore him so he ignores them.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.