Stacks, as we defined earlier, is a Bitcoin layer. Rollups are a different type of scaling solution, but they are not layers. In recent months, comparisons have been made between Stacks and sovereign rollups, in particular, with key differences highlighted in a GitHub entry. Most notably, rollups require tokens to be moved in and out of L1 (in this case, the Bitcoin L1). This is why the development and launch of sBTC will be crucial for new technologies like rollups that require BTC to be moved in and out of the Bitcoin L1.
Additionally, sovereign rollups, in particular, publish the full rollup data on to L1. Stacks, on the other hand, publishes hashes of data to every Bitcoin block.