If you want to block them yourself, you can do so once they go live by selecting "Block <domain>" in the context menu of one of their posts or accounts.

If you want to block them ahead of time, you can do so via the CSV import. On https://chaos.social/settings/import, select "Domain blocking list" and upload a file containing "threads.net", (and to be safe, "threads.instagram.net").
Here's a file like that: https://gist.githubusercontent.com/rixx/cff5003c5054b9288d67552f544d26bc/raw/e81dd45648367b0ace0646675255f2b154368dd0/blocked_domains.csv

You can see your blocked domains at https://chaos.social/domain_blocks

Thank you for your patience. After observing the first 24 hours of Threads, we decided to block threads.net (in advance of them at some point joining the Fediverse).

There are openly, aggressively transphobic accounts on Threads.net with no visible attempt at moderation. We would defederate from any other Fediverse instance with that behaviour and no moderation, and there is no reason to treat threads.net any different.

@Silicium @ordnung yes, then leave this instance where you had the rules available beforehand, read them, and accepted them. I'm not sure whether you've realised this whole decentralization thing and that this is the so-called fediverse. New thing, so not everyone may be aware, but the point about is that you can choose what kind of moderation you want.

You chose moderation by chaos.social. Now you whine about getting moderation by chaos.social. I'm sorry, but my condolences are limited here.