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.

@ordnung being a heavy user on #Threads since the launch, I didn't stumble upon a single posting or account that shared transphobic content. Not one.

Instead #Twitter is full of postings with screenshots and accounts that were banned, closed/deactivated on Threads... so there's obviously quite some moderation going on, which of course caused a censorship outcry on Twitter

Do you have any examples for your accusations?

@343max

du wirst spezifisch auf die usual suspects gehen muessen. Ich habe nicht ein Posting bei mir in den Feed bekommen, dass auch nur ansatzweise in die Richtung dieser Ballerbirnen schoss.

Nicht eines!

Der pauschale Block von wohl inzischen gut ueber 100 Mio User:innen duerfte wohl so ziemlich die groesste Sippenhaft in der Netzhistorie sein. Kann man machen!

@ordnung