There are currently no regular public codes you can use in Steal a Brainrot on Roblox.
Current code situation
Most up-to-date guides explain that the game does not yet have an in‑game code redeem system, so no standard “promo codes” (like many other Roblox games have) are available. Some sites even note that because there’s no code system, there are also no expired codes listed for the game.
Special or limited codes
A recent update mentions a unique “Festive 67 Plush” code that was emailed only to people who bought a specific plush toy, and it is limited in quantity. Aside from this kind of special merch code, there is still no general list of reusable codes for all players.
What you can do instead
Because there are no normal codes, progress mainly comes from playing: building your base, stealing rare Brainrots, and using traits and events to boost your income. Checking recent community news or official channels from the game’s creators is the best way to see if a real code system gets added in the future.