[gemma 3] multimodal checkpoints + AutoModelForCausalLM (#36741)

tests/models/gemma3/test_modeling_gemma3.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 """Testing suite for the PyTorch Gemma3 model."""
 
+import tempfile
 import unittest
 
 import pytest
@@ -339,6 +340,18 @@ class Gemma3Vision2TextModelTest(ModelTesterMixin, GenerationTesterMixin, unitte
     def test_flex_attention_with_grads(self):
         pass
 
+    def test_automodelforcausallm(self):
+        """
+        Regression test for #36741 -- make sure `AutoModelForCausalLM` works with a Gemma3 config, i.e. that
+        `AutoModelForCausalLM.from_pretrained` pulls the text config before loading the model
+        """
+        config = self.model_tester.get_config()
+        model = Gemma3ForConditionalGeneration(config)
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            model.save_pretrained(tmp_dir)
+            for_causal_lm = AutoModelForCausalLM.from_pretrained(tmp_dir)
+            self.assertIsInstance(for_causal_lm, Gemma3ForCausalLM)
+
 
 @slow
 @require_torch_gpu