Do I use 1041-A or 5227 for a split interest trust return?
According to Form 1041-A Instructions, page 3:
Split-interest trusts as described in section 4947(a)(2) do not file Form 1041-A. These types of trusts file Form 5227, Split-Interest Trust Information Return, which meets the section 6034 filing requirements.
Form 5227 Instructions state that the following types of organizations should instead use Form 5227:
All charitable remainder trusts described in section 664 must file Form 5227. All pooled income funds described in section 642(c)(5) and all other trusts such as charitable lead trusts that meet the definition of a split-interest trust under section 4947(a)(2) must file Form 5227 unless the Exception (listed on page 1 of Form 5227 instructions) applies.