At Babylon, the native Olympia token model was upgraded to a much more powerful resource model, and all pre-existing tokens were converted to fungible resources (note that there were no non-fungible tokens on Olympia, though some community NFT-related projects had previously distributed fungible placeholder tokens).
The configuration of the new resource-based tokens were set to mimic the behavior of those tokens on Olympia. Symbol, name, and description were mapped to metadata fields. Tokens which were set to have a mutable supply at Olympia now have a badge on Babylon created with the authority to mint and burn them, and that badge was placed in a smart account controlled by the same key which had that authority on Olympia.
While there is no set maximum supply of any resource on Babylon, the maximum amount that can be minted in a single action is 2^152 atto. Any Olympia tokens with a supply exceeding 2^152 were proportionally reduced such that the migrated supply did not exceed 2^152. That is, if you had a token whose supply was 10 * 2^152 atto, any accounts holding those tokens would wind up with 1/10th what they held prior to migration.
New resource behaviors which were not possible on Olympia tokens were locked off from the migrated assets, so that holders can be confident that nothing surprising can suddenly happen with their tokens that could not happen on Olympia.
Developers who released a token on Olympia and now wish to take advantage of the new features offered by resources may wish to re-create a representation on Babylon, and can easily deploy a simple redemption component which exchanges the new resource for the old one.