diff --git a/research/vortex_exact_attention/DESIGN.md b/research/vortex_exact_attention/DESIGN.md
index ad54b64..8c226bc 100644
--- a/research/vortex_exact_attention/DESIGN.md
+++ b/research/vortex_exact_attention/DESIGN.md
@@ -166,3 +166,19 @@ boundary rather than a temporal schedule rearrangement.
 Stop immediately on changed KV order, any material score tensor, nonzero output
 difference, forced local spilling, inability to beat the `220 ms` model gate, or
 fallback to Sage2 for main computation.
+
+## Interface And Future Ulysses Layout
+
+The isolated API consumes projection-strided BF16 NHD views directly. Its work
+descriptor must carry `q_start`, `q_count`, `kv_count`, `head_start`,
+`head_count`, source token/head strides, destination token/head strides, and a
+future rank destination. No HND transpose or contiguous input copy is allowed.
+
+Output stores land directly in token-major `[token, local_head*128+d]` rows for
+the local output projection. Ragged local token counts and nonzero destination
+offsets are legal, but each rank must receive the globally ordered KV sequence
+before attention. Independently normalized KV partials must never be merged.
+
+VEA-B is optimized first for the single-GPU Q128 shape. A future SM120/SM100 or
+Ulysses schedule may choose Q64 or a different producer geometry, but it must
+retain this numerical and descriptor contract and pass separately tuned gates.