With the final appeal being denied, I thought they had no further chance.
From Reuters on twitter:
BBC: Wa Lone poses with wife Pan Ei Mon and daughter, along with Reuters reporter Kyaw
Wa Lone had a daughter born while he was in prison.
Preliminarily, it appears that a Brit doing advisory work for the government there may have been involved in their inclusion in an annual amnesty release:
The Reuters journalists were released at the prison to representatives of Reuters and to Lord Ara Darzi, a British surgeon and health care expert who has served as a member of an advisory group to Myanmars government on reforms in Rakhine State.
...
Darzi said discussions about the pardon for Wa Lone and Kyaw Soe Oo had involved the Myanmar government, Reuters, the United Nations and representatives of other governments. He did not elaborate.
...
A Reuters spokesman said Darzi had made the company aware earlier this year of his efforts to secure the journalists release.
Darzi has been a member of an advisory commission that was formed in 2016 to see through the advice from a panel headed by former U.N. chief Kofi Annan on solving the long-running conflict in western Myanmars Rakhine State.
More from Reuters along with a photo slide-show after their release:
https://www.reuters.com/article/us-myanmar-journalists/reuters-reporters-jailed-in-myanmar-freed-from-prison-after-more-than-500-days-idUSK