A memo signed by Obama last June extending benefits to federal employees of same-sex partners will begin taking effect next month, and has been broadened "to include same-sex domestic partners of eligible federal workers, U.S. Postal Service workers and federal retirees" according to the Washington Post:

"OPM will not extend access to opposite-sex domestic partners, because they can obtain the insurance through marriage, 'an option not currently available to same-sex domestic partners,' the agency wrote in Tuesday's Federal Register.

OPM said same-sex couples can visit www.ltcfeds.com to complete a form that states they are each other's domestic partner and intend to stay together indefinitely. The federal worker must submit the form to their employer. Couples will not be required to provide further proof of the relationship, OPM said, because that 'would impose a greater burden on domestic partners than other qualified relatives.' The agency said it does not ask opposite-sex couples for bank statements or other proof of marriage."

Changes are detailed here.