Result of EXLA.CustomCall.call/4 when lowering a tagged Nx.block/4 to stablehlo.custom_call.

• call_target_name — XLA FFI handler name (call_target_name on the op).

• attributes — Optional {name, attr} pairs, default [], merged into the backend_config dictionary on stablehlo.custom_call (StableHLO’s name for that attribute). Each name must be a BEAM binary MLIR identifier; each attr must be a BEAM binary with valid MLIR attribute syntax for the RHS after name = (for example {"k", "42 : i64"}). An empty list omits the dictionary from the op.

• operand_element_types — How operand SSA values are presented to the handler:

  • :default — use each lowered operand’s element type as produced from the block inputs. No extra converts.

  • [Nx.Type.t(), ...] — one type per block input, same order and length as Nx.block/4 inputs. Before building the custom call, each operand is converted (StableHLO convert) when its element type differs from the requested type; shapes are unchanged. Use this when the native kernel’s FFI signature expects dtypes that may differ from the traced expression types (for example after promotion rules).