Legal Question in Landlord & Tenant Law in California

Not required, no, but if they are a true sub-tenant, they are legally subject to the terms of the master lease. So it's not a good idea to sublease without having a copy. Also, if the property is in the Berkeley part of 94706, it may be illegal for the master tenant to charge more rent for the sublease than the master tenant pays the landlord. So if the master tenant tries to do that and to cover it up by refusing to provide a copy of the master lease, that could be charged as fraud.