diff --git a/packages/overture-schema-pyspark/changelog.d/659.bugfix.md b/packages/overture-schema-pyspark/changelog.d/659.bugfix.md
new file mode 100644
index 000000000..133bc11dd
--- /dev/null
+++ b/packages/overture-schema-pyspark/changelog.d/659.bugfix.md
@@ -0,0 +1 @@
+Moved `pyspark` from a hard dependency to the `spark` optional extra, so installing `overture-schema-pyspark` no longer resolves `pyspark` on runtimes (Glue, EMR) that already bundle their own. Standalone environments need `pip install overture-schema-pyspark[spark]`. Importing the package without PySpark installed now raises an actionable `ModuleNotFoundError` pointing at that extra, instead of a bare "No module named 'pyspark'".
diff --git a/packages/overture-schema-pyspark/pyproject.toml b/packages/overture-schema-pyspark/pyproject.toml
index 6e72bc93c..a280bf72c 100644
--- a/packages/overture-schema-pyspark/pyproject.toml
+++ b/packages/overture-schema-pyspark/pyproject.toml
@@ -6,7 +6,6 @@ build-backend = "uv_build"
 dependencies = [
     "click>=8.0",
     "overture-schema-system>=0.1.1",
-    "pyspark>=3.4",
 ]
 description = "PySpark validation expressions for Overture Maps data"
 license = "MIT"
@@ -14,6 +13,9 @@ name = "overture-schema-pyspark"
 requires-python = ">=3.10"
 version = "0.1.1"
 
+[project.optional-dependencies]
+spark = ["pyspark>=3.4"]
+
 [project.scripts]
 overture-validate = "overture.schema.pyspark.cli:validate_cli"
 
diff --git a/packages/overture-schema-pyspark/src/overture/schema/pyspark/__init__.py b/packages/overture-schema-pyspark/src/overture/schema/pyspark/__init__.py
index 8841ae9f4..33b794e27 100644
--- a/packages/overture-schema-pyspark/src/overture/schema/pyspark/__init__.py
+++ b/packages/overture-schema-pyspark/src/overture/schema/pyspark/__init__.py
@@ -1,5 +1,19 @@
 """PySpark validation expressions for Overture Maps data."""
 
+# pyspark is an optional extra (the `spark` extra): a bare install lets this
+# package's console script and metadata resolve, but every submodule needs
+# pyspark to do anything. Guard the import directly so a missing pyspark gives
+# an actionable message; anything else this package imports surfaces its own
+# error through the real imports below.
+try:
+    import pyspark  # noqa: F401
+except ModuleNotFoundError as e:
+    raise ModuleNotFoundError(
+        "overture-schema-pyspark requires PySpark, which isn't installed. "
+        "Install it with `pip install overture-schema-pyspark[spark]`, or run "
+        "in an environment that already provides PySpark (e.g. a Spark cluster)."
+    ) from e
+
 from .check import Check, CheckShape
 from .schema_check import SchemaMismatch, compare_schemas
 from .validate import (
diff --git a/uv.lock b/uv.lock
index 5e0bcfd1a..bead56ba9 100644
--- a/uv.lock
+++ b/uv.lock
@@ -9,7 +9,7 @@ resolution-markers = [
 ]
 
 [options]
-exclude-newer = "0001-01-01T00:00:00Z" # This has no effect and is included for backwards compatibility when using relative exclude-newer values.
+exclude-newer = "2026-08-06T18:30:08.560594Z"
 exclude-newer-span = "P1W"
 
 [manifest]
@@ -363,7 +363,7 @@ name = "exceptiongroup"
 version = "1.3.1"
 source = { registry = "https://pypi.org/simple" }
 dependencies = [
-    { name = "typing-extensions" },
+    { name = "typing-extensions", marker = "python_full_version < '3.11'" },
 ]
 sdist = { url = "https://files.pythonhosted.org/packages/50/79/66800aadf48771f6b62f7eb014e352e5d06856655206165d775e675a02c9/exceptiongroup-1.3.1.tar.gz", hash = "sha256:8b412432c6055b0b7d14c310000ae93352ed6754f70fa8f7c34141f91c4e3219", size = 30371, upload-time = "2025-11-21T23:01:54.787Z" }
 wheels = [
@@ -1042,6 +1042,10 @@ source = { editable = "packages/overture-schema-pyspark" }
 dependencies = [
     { name = "click" },
     { name = "overture-schema-system" },
+]
+
+[package.optional-dependencies]
+spark = [
     { name = "pyspark" },
 ]
 
@@ -1049,8 +1053,9 @@ dependencies = [
 requires-dist = [
     { name = "click", specifier = ">=8.0" },
     { name = "overture-schema-system", editable = "packages/overture-schema-system" },
-    { name = "pyspark", specifier = ">=3.4" },
+    { name = "pyspark", marker = "extra == 'spark'", specifier = ">=3.4" },
 ]
+provides-extras = ["spark"]
 
 [[package]]
 name = "overture-schema-system"