Domestic Partnerships were created in Washington State as a sort of marriage substitute. They are codified in RCW 26.60. To have a Domestic Partnership in Washington, you need to register the partnership with the state.
To register a Domestic Partnership in Washington you must fall into one of two categories – be a same sex couple, or one partner must be over 62 years of age. However, as of June 30, 2014, the first category is being eliminated and only couples where one partner is over 62 will still be able to register.
The two categories were created for very different reasons. The same sex couple Domestic Partnership was created to provide a marriage equivalent for couples who were not able to legally marry in the state based on being of the same gender. The category for couples where one partner is over 62 (often a heterosexual couple) was created to provide a marriage like status for older couples who might face negative financial impacts from marrying, such as to their social security payments.
Several years after the Domestic Partnership statute was enacted, Washington finally passed new legislation allowing same sex couples to marry. This then eliminated the need to have a marriage equivalent for same sex couples. This is why the ability for same sex couples to register a Domestic Partnership is being eliminated.
This still left the question of what to do about the same sex couples that had already registered. The decision was made by the state to convert those Domestic Partnerships to marriages as of June 30, 2014 without any further action on the part of those couples. I assume the reasoning was that the couples who registered would have married instead if that had been an option. However, if at least partner is over 62, that Domestic Partnership will not be automatically converted to a marriage.
I have heard from some couples who do not wish to have their partnership converted to a marriage. If at least one of the partners is not over 62, the couple will need to dissolve the partnership to avoid having it convert to a marriage. The process for dissolving a Domestic Partnership is similar to that for dissolving a marriage (i.e. a divorce). One issue that can create problems is if the couple has moved out of Washington State since registering. If neither party is still a resident of Washington (which means living here with the intent to continue to live here), then they may not be able to obtain a dissolution. Such a couple may need to move back to Washington, or to another state that recognizes their partnership, in order to obtain their dissolution.