diff --git a/pyproject.toml b/pyproject.toml
index ed3724ac..778862a7 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,6 +50,10 @@ dependencies = [
 # https://peps.python.org/pep-0621/#dependencies-optional-dependencies
 [project.optional-dependencies]
 models = ["transformers<4.40"]
+# Multiscale UMAP montages for the diffae interpretability figures. A git
+# dependency, so it is kept out of the default install; only
+# models/interpretability/diffae/viewer/ imports it.
+diffae = ["latent-lens @ git+https://github.com/czi-ai/latent-lens"]
 test = ["pytest>=6.0", "pytest-cov"]
 dev = [
     "ipykernel",
diff --git a/src/ops_model/models/interpretability/diffae/viewer/build_umap_montage.py b/src/ops_model/models/interpretability/diffae/viewer/build_umap_montage.py
index 87bd16cf..6d16a3ee 100644
--- a/src/ops_model/models/interpretability/diffae/viewer/build_umap_montage.py
+++ b/src/ops_model/models/interpretability/diffae/viewer/build_umap_montage.py
@@ -15,7 +15,6 @@
 import anndata as ad
 from PIL import Image
 
-from latent_lens import MontageConfig, build_montage
 
 from ..classifier.config import slugify
 from .precompute import VIEWER_ALPHAS
@@ -79,6 +78,10 @@ def montage_from_cache(h5ad, out_zarr, cell=0, alpha=2.0, modality="phase", grai
     placed at the gene's position in `embedding` (obsm X_<embedding>, e.g. umap or phate).
     Crops kept GRAYSCALE (white category tint). crop_size=256 sharp; px_per_umap≈22×crop fills canvas.
     `border_field` (an obs column, e.g. 'leiden_r4') draws a per-cell colored border keyed on that group."""
+    # Lazy: latent-lens is the `diffae` extra, not a default install
+    # (`uv sync --extra diffae`, or `pip install ops_model[diffae]`).
+    from latent_lens import MontageConfig, build_montage
+
     al = list(VIEWER_ALPHAS)
     ai = int(np.argmin([abs(a - alpha) for a in al]))     # frame index for the requested α
     a0 = int(np.argmin([abs(a) for a in al]))             # α=0 frame index (shared anchor recon)