diff --git a/Makefile b/Makefile
index 1f58a9d..5b244d0 100644
--- a/Makefile
+++ b/Makefile
@@ -82,7 +82,7 @@ py-test: py-dev
 
 py-test-benchmarks: py-dev
 	@command -v $(UV) >/dev/null 2>&1 || (echo "uv not found; install from https://docs.astral.sh/uv/" && exit 1)
-	cd atompack-py && UV_CACHE_DIR=$(UV_CACHE_DIR) $(UV) run --extra dev --locked pytest tests/benchmarks
+	cd atompack-py && UV_CACHE_DIR=$(UV_CACHE_DIR) $(UV) run --extra dev --extra benchmarks --locked pytest tests/benchmarks
 
 docs-sync:
 	@command -v $(UV) >/dev/null 2>&1 || (echo "uv not found; install from https://docs.astral.sh/uv/" && exit 1)
diff --git a/atompack-py/benchmarks/README.md b/atompack-py/benchmarks/README.md
index 035765b..a4162f0 100644
--- a/atompack-py/benchmarks/README.md
+++ b/atompack-py/benchmarks/README.md
@@ -64,7 +64,8 @@ Notes:
 - `get_molecules_flat(...)` remains the fastest tensor-batch path when the
   consumer can work with concatenated arrays directly.
 - `hdf5_soa` reflects the usual chunked-dataset HDF5 layout used for
-  fixed-shape materials data and is part of the default benchmark environment.
+  fixed-shape materials data; install with `pip install atompack-db[benchmarks]`
+  to pull in the `h5py` dependency.
 - `lmdb_packed` now participates in the synthetic custom-property variants in
   this suite too; `lmdb_soa` remains the builtins-only helper baseline.
 - In this suite, `hdf5_soa` is intentionally read one molecule at a time so it
@@ -330,8 +331,9 @@ tuning that matters most for dataloader-like access:
 - reader-side raw chunk cache sizing through `h5py` open options
 - batch reads that regroup requested indices by chunk before rebuilding payloads
 
-This backend is included in the default benchmark environment through the base
-project dependencies.
+This backend depends on `h5py`, which is shipped as the `[benchmarks]` extra:
+install with `pip install atompack-db[benchmarks]` (or `make py-test-benchmarks`
+which now uses both the `dev` and `benchmarks` extras).
 
 ### `atom_lmdb_soa.py`
 
diff --git a/atompack-py/pyproject.toml b/atompack-py/pyproject.toml
index 1fbb7b4..7988c45 100644
--- a/atompack-py/pyproject.toml
+++ b/atompack-py/pyproject.toml
@@ -32,7 +32,6 @@ classifiers = [
     "Programming Language :: Python :: 3.14",
 ]
 dependencies = [
-    "h5py>=3.10",
     "huggingface_hub>=0.24",
     "numpy>=1.20",
 ]
@@ -51,6 +50,12 @@ dev = [
     "mypy",
     "ruff",
 ]
+# Used only by the comparison scripts under atompack-py/benchmarks/. Not
+# imported anywhere under python/atompack/, so it has no business in the
+# base wheel — pulls ~50 MB of HDF5 binaries onto every install.
+benchmarks = [
+    "h5py>=3.10",
+]
 
 [tool.maturin]
 python-source = "python"
diff --git a/atompack-py/uv.lock b/atompack-py/uv.lock
index e4ef7f7..02f311c 100644
--- a/atompack-py/uv.lock
+++ b/atompack-py/uv.lock
@@ -169,9 +169,6 @@ name = "atompack-db"
 version = "0.2.1"
 source = { editable = "." }
 dependencies = [
-    { name = "h5py", version = "3.11.0", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.9'" },
-    { name = "h5py", version = "3.14.0", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version == '3.9.*'" },
-    { name = "h5py", version = "3.16.0", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.10'" },
     { name = "huggingface-hub", version = "0.36.2", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.9'" },
     { name = "huggingface-hub", version = "1.8.0", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.9'" },
     { name = "numpy", version = "1.24.4", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.9'" },
@@ -181,6 +178,11 @@ dependencies = [
 ]
 
 [package.optional-dependencies]
+benchmarks = [
+    { name = "h5py", version = "3.11.0", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.9'" },
+    { name = "h5py", version = "3.14.0", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version == '3.9.*'" },
+    { name = "h5py", version = "3.16.0", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.10'" },
+]
 dev = [
     { name = "mypy", version = "1.14.1", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.9'" },
     { name = "mypy", version = "1.19.1", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.9'" },
@@ -224,7 +226,7 @@ docs = [
 
 [package.metadata]
 requires-dist = [
-    { name = "h5py", specifier = ">=3.10" },
+    { name = "h5py", marker = "extra == 'benchmarks'", specifier = ">=3.10" },
     { name = "huggingface-hub", specifier = ">=0.24" },
     { name = "mypy", marker = "extra == 'dev'" },
     { name = "numpy", specifier = ">=1.20" },
@@ -232,7 +234,7 @@ requires-dist = [
     { name = "pytest-benchmark", marker = "extra == 'dev'" },
     { name = "ruff", marker = "extra == 'dev'" },
 ]
-provides-extras = ["dev"]
+provides-extras = ["dev", "benchmarks"]
 
 [package.metadata.requires-dev]
 docs = [