Functions pertaining to talents and specializations are renamed:
GetActiveTalentGroup → GetActiveSpecGroup (NB: player character-only)
SetActiveTalentGroup → SetActiveSpecGroup
GetNumTalentGroups → GetNumSpecGroups
GetPrimaryTalentTree → GetSpecialization
GetUnspentTalentPoints → GetNumUnspentTalents
GetNumTalentTabs → GetNumSpecializations
GetTalentTabInfo → GetSpecializationInfo
GetTalentTreeRoles → GetSpecializationRole
Many party/raid-related functions and events are merged into group variants.
IsRaidLeader, IsPartyLeader, UnitIsPartyLeader → UnitIsGroupLeader
IsRaidOfficer, UnitIsRaidOfficer → UnitIsGroupAssistant
GetNumPartyMembers, GetRealNumPartyMembers → GetNumSubgroupMembers
GetNumRaidMembers, GetRealNumRaidMembers → GetNumGroupMembers (NB: non-0 in any group, including parties; use IsInRaid to check for group type)
RAID_ROSTER_UPDATE, PARTY_MEMBERS_CHANGED → GROUP_ROSTER_UPDATE
Functions pertaining to Real/Fake groups (home realm and instance/battleground-specific groups) are removed. Instead, group functions take an argument specifying which group you want to query:
LE_PARTY_CATEGORY_HOME will query information about your "real" group -- the group you were in on your Home realm, before entering any instance/battleground.
LE_PARTY_CATEGORY_INSTANCE will query information about your "fake" group -- the group created by the instance/battleground matching mechanism.
Achievement API:
GetAchievementCriteriaInfo split into two separate functions:
By criteria order: GetAchievementCriteriaInfo(achievementID, criteriaIndex)
By internal criteria ID: GetAchievementCriteriaInfoByID(achievementID, criteriaID)