A community property survivorship agreement is similar to a will but it does not have to be executed with the formalities required of a will. The agreement has to be signed by both parties and has to use certain words as described by the statute.
The effect of the agreement is to transfer all of the community property owned by husband and wife to the survivor when one dies. That sounds like a will doesn't it? However, it is not a will but is just an agreement. Since it is an agreement and not a will, the requirements of execution under a will did not apply to an agreement. The agreement doesn't transfer separate property, just community property. 112.001.
I have an article on my blog about a 2019 case involving community property survivorship agreements. You can view that here.