must implement and maintain a standards-based Application Programming Interface (API)
Here it says that the MA plans must be "standards-based".
must implement and maintain a standards-based Application Programming Interface (API)
Here it says that the MA plans must be "standards-based".
without special effort
This is the simple phrase that means it must be standards compliant.
This is the requirements for Medicare Advantage Payers to implement directories that explain coverage contents.
In the Interoperability and Patient Access final rule (CMS-9115-F), CMS encouraged MA-PD plans to build a Provider Directory API that is conformant to the Health Level Seven International® (HL7®) PDex Plan-Net Implementation Guide (85 FR 25529).
Apparently PDex standard is "encouraged." but not required.