"Our initial review indicates that CMS has been responsive to many of the concerns raised by the AMA, and in the days ahead, the AMA will conduct a comprehensive review of the final rule to ensure that it promotes flexibility and innovation in the delivery of care to help meet the unique needs of all patients," said the association in a statement, which noted what it saw as improvements over what the administration had previously proposed.

A number of members of Congress signaled ambivalence but stopped short of embracing or denouncing the new regulations.

"Transforming something of this size is something we have focused on with great care," Andy Slavitt, head of the federal Centers for Medicare and Medicaid Services, told the AP.

The new regulations will not be fully implemented until 2019.

The new regulations offer medical providers two options for billing Medicare.

The track that most are expected to take is the Merit-Based Incentive Payment Systems (MIPS), which will tie parts of the reimbursement to certain performance measures. CMS anticipates roughly 600,000 doctors, nurses and other medical professionals to be paid that way, at least in the first year of the new system.

More ambitious providers can also opt to develop an Alternative Payment Model, which offers higher risk and higher reward. There is a wide range of acceptable "alternatives," that providers can submit for approval to CMS, which said it expects between 70,000 and 120,000 medical professionals to participate in the track.

In addition, there are an estimated 380,000 clinicians who will continue to operate on a fee-for-service basis because they don't do enough business with Medicare.

That compromise was extracted from the administration by the AMA and other physician groups.