Coin categories (GET /v1/categories): each category id and name with the catalog uids that belong to it, for example layer-1 or stablecoins. Join it with uids from get_rates or search_assets to group holdings. It changes about once a day; as_of says when it was refreshed. A coin can be in several categories, and only the larger coins of a category are listed. Categories without a catalog member are omitted. The result grows with the catalog (one uid list per category, both copies of the result). not_ready (503) before the first daily refresh; not_found when the server has categories switched off.