diff --git a/pyproject.toml b/pyproject.toml
index 3c6fb88e..3f576949 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -65,7 +65,9 @@ langcache = ["langcache>=0.11.0"]
 # importing. New text embeddings should use the `google-genai` extra below.
 vertexai = [
     "google-cloud-aiplatform>=1.26,<2.0.0",
-    "protobuf>=5.28.0,<6.0.0",
+    # Uncapped on purpose: nothing here imports protobuf, so the bound belongs
+    # to google-cloud-aiplatform, which declares its own.
+    "protobuf>=5.28.0",
 ]
 # Modern Google backend (Vertex AI + Gemini Developer API) for GoogleGenAIVectorizer.
 google-genai = ["google-genai>=1.0.0"]
@@ -87,7 +89,7 @@ all = [
     "sentence-transformers>=5.2.0,<6",
     "langcache>=0.11.0",
     "google-cloud-aiplatform>=1.26,<2.0.0",
-    "protobuf>=5.28.0,<6.0.0",
+    "protobuf>=5.28.0",
     "google-genai>=1.0.0",
     "boto3>=1.36.0,<2",
     "urllib3<2.8.0",
diff --git a/uv.lock b/uv.lock
index fee99270..2c013a33 100644
--- a/uv.lock
+++ b/uv.lock
@@ -4975,8 +4975,8 @@ requires-dist = [
     { name = "openai", marker = "extra == 'openai'", specifier = ">=1.1.0" },
     { name = "pillow", marker = "extra == 'all'", specifier = ">=11.3.0" },
     { name = "pillow", marker = "extra == 'pillow'", specifier = ">=11.3.0" },
-    { name = "protobuf", marker = "extra == 'all'", specifier = ">=5.28.0,<6.0.0" },
-    { name = "protobuf", marker = "extra == 'vertexai'", specifier = ">=5.28.0,<6.0.0" },
+    { name = "protobuf", marker = "extra == 'all'", specifier = ">=5.28.0" },
+    { name = "protobuf", marker = "extra == 'vertexai'", specifier = ">=5.28.0" },
     { name = "pydantic", specifier = ">=2,<3" },
     { name = "pydantic-settings", marker = "extra == 'mcp'", specifier = ">=2.0,<3" },
     { name = "python-ulid", specifier = ">=3.0.0" },