More space per chicken is just one of the requirements. Probably the most important requirement is to use higher welfare breeds, which generally grow more slowly. But there are more requirements regarding lighting, enrichments, etc. You can see the full ask in the European Chicken Commitment. Asks for other regions are similar and can be seen here.
Off-topic but what do broiler chicken campaigns look like typically? I know for hens it’s cage-free, is it just more space per chicken for broilers?
More space per chicken is just one of the requirements. Probably the most important requirement is to use higher welfare breeds, which generally grow more slowly. But there are more requirements regarding lighting, enrichments, etc. You can see the full ask in the European Chicken Commitment. Asks for other regions are similar and can be seen here.