There is a mixed information on the internet about the number of CNAME records that can be defined for a domain. Some say that there is no limit and millions of CNAME records can be created. Others say that it depends on a provider that can enforce limits.
I can’t find exact answer about AWS Route 53 limits. Will Route 53 support 200K+ CNAME records per hosted zone?
The limits are not expressed directly in number of subdomains or cnames, but rather in number of records and hosted zones, among other things.
Therefore, there is 10,000 records per hosted zone, but it can be increased. Also you can have 500 hosted zones per account.