How does Instagram's OG username interception work? (Checkers/Auto-claimers) [closed]

I recently came across a Telegram channel where a guy sells short and catchy Instagram usernames (3–4 letters, clean words, etc.). From time to time, he shows small parts of his Python scripts — you can see a multithreaded checker, threading.Lock(), and statuses like Checked, Avail, Block, UnAvail. Obviously, he hides the actual source code and core logic.

I understand the basic idea: a script loads wordlists and keeps sending requests to Instagram to check username availability. As soon as something returns Avail, it instantly tries to claim it.

But there are a few architectural details I’m still curious about. If anyone has experience with this kind of tooling or understands how it works under the hood, I’d appreciate some insights:

Where do they get their datasets from? Is it just brute-forcing all possible 3–4 character combinations, using leaked username dumps, or scraping handles from platforms like TikTok/Twitter?

How do they deal with rate limits? Instagram is pretty aggressive with anti-spam — regular IPv4 proxies get hit with 429s almost immediately. Are they using large pools of rotating residential/mobile proxies?

What’s the deal with “dead” usernames? For example, if I try a 4-letter username (like @guhw), it doesn’t show up in search, but during signup it says “Unavailable.” I assume it’s tied to a deleted or permanently banned account. Can these checkers ever reclaim such usernames, or do they only catch ones that were recently released (after the cooldown period)?

Would love to hear any technical insights about how this market actually works behind the scenes.