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 you want transphobic content to be unmoderated?

@ordnung

@Silicium I do want that hive of scum and villainy excluded from the Fediverse, especially as Meta is obviously trying to EEE ActivityPub. If you want your bath in that environment, feel free to go there, but please refrain from even attempting to force that on all the others here.

@ordnung

@wonka
Reading the EEE thing... Microsoft lost at least the browser fight...
Java is still there....
So not sure if it always works...

@Silicium @ordnung

@joergi Browsers are not the example you think it is. All relevant browsers are Chromium based now, except Firefox.

@Silicium @ordnung