diff --git a/pkgs/by-name/op/open-webui/package.nix b/pkgs/by-name/op/open-webui/package.nix
index a8888d43f8c7..73a80c60e6e4 100644
--- a/pkgs/by-name/op/open-webui/package.nix
+++ b/pkgs/by-name/op/open-webui/package.nix
@@ -163,6 +163,7 @@ python312.pkgs.buildPythonApplication rec {
       requests
       restrictedpython
       sentence-transformers
+      sentencepiece
       soundfile
       tiktoken
       transformers
diff --git a/pkgs/development/python-modules/sentence-transformers/default.nix b/pkgs/development/python-modules/sentence-transformers/default.nix
index 5ecd35e78a8c..808613591d94 100644
--- a/pkgs/development/python-modules/sentence-transformers/default.nix
+++ b/pkgs/development/python-modules/sentence-transformers/default.nix
@@ -2,14 +2,17 @@
   lib,
   buildPythonPackage,
   fetchFromGitHub,
+  pythonOlder,
 
   # build-system
   setuptools,
 
   # dependencies
+  accelerate,
+  datasets,
   huggingface-hub,
-  nltk,
-  numpy,
+  optimum,
+  pillow,
   scikit-learn,
   scipy,
   sentencepiece,
@@ -19,8 +22,6 @@
   transformers,
 
   # tests
-  accelerate,
-  datasets,
   pytestCheckHook,
   pytest-cov-stub,
 }:
@@ -30,6 +31,8 @@ buildPythonPackage rec {
   version = "3.4.1";
   pyproject = true;
 
+  disabled = pythonOlder "3.9";
+
   src = fetchFromGitHub {
     owner = "UKPLab";
     repo = "sentence-transformers";
@@ -41,23 +44,28 @@ buildPythonPackage rec {
 
   dependencies = [
     huggingface-hub
-    nltk
-    numpy
+    pillow
     scikit-learn
     scipy
-    sentencepiece
-    tokenizers
     torch
     tqdm
     transformers
   ];
 
+  optional-dependencies = {
+    train = [
+      accelerate
+      datasets
+    ];
+    onnx = [ optimum ] ++ optimum.optional-dependencies.onnxruntime;
+    # onnx-gpu = [ optimum ] ++ optimum.optional-dependencies.onnxruntime-gpu;
+    # openvino = [ optimum-intel ] ++ optimum-intel.optional-dependencies.openvino;
+  };
+
   nativeCheckInputs = [
-    accelerate
-    datasets
-    pytestCheckHook
     pytest-cov-stub
-  ];
+    pytestCheckHook
+  ] ++ lib.flatten (builtins.attrValues optional-dependencies);
 
   pythonImportsCheck = [ "sentence_transformers" ];