Almost all housing providers must accept emotional support animals under federal Fair Housing rules, so you are not obliged to tell your landlord about your ESA. As emotional support animals are not considered pets, building’s standard policies regarding pets do not apply to ESA.
However, it is an excellent idea to let your landlord know about your emotional support animal and give them an ESA letter before you sign the lease. ESA letters for housing purposes technically do not expire under Fair Housing rules. But some landlords can demand a more recent dated letter.