diff --git a/python/packages/ag-ui/agent_framework_ag_ui/_message_adapters.py b/python/packages/ag-ui/agent_framework_ag_ui/_message_adapters.py
index 35ddd46be8..c5a4d04cb3 100644
--- a/python/packages/ag-ui/agent_framework_ag_ui/_message_adapters.py
+++ b/python/packages/ag-ui/agent_framework_ag_ui/_message_adapters.py
@@ -360,9 +360,10 @@ def _extract_multimodal_source_fields(
 ) -> tuple[str | None, str | None, str | None, str | None]:
     """Extract ``(url, data, binary_id, mime_type)`` from an AG-UI multimodal part.
 
-    Handles both the current AG-UI spec (``source.value`` for base64 payloads) and the
-    legacy ``source.data`` field for backward compatibility. Returned values are the
-    raw extracted strings (or ``None`` when absent); callers apply their own defaults.
+    Handles both the current AG-UI spec (``source.value`` for both URL and base64
+    payloads) and the legacy ``source.url``/``source.data`` fields for backward
+    compatibility. Returned values are the raw extracted strings (or ``None`` when
+    absent); callers apply their own defaults.
     """
     mime_type = cast(str | None, part.get("mimeType") or part.get("mime_type"))
     url = cast(str | None, part.get("url") or part.get("uri"))
@@ -378,7 +379,7 @@ def _extract_multimodal_source_fields(
             mime_type = source_mime
 
         if source_type in {"url", "uri"}:
-            url = cast(str | None, source_dict.get("url") or source_dict.get("uri"))
+            url = cast(str | None, source_dict.get("value") or source_dict.get("url") or source_dict.get("uri"))
         elif source_type in {"base64", "data", "binary"}:
             data = cast(str | None, source_dict.get("value") or source_dict.get("data"))
         elif source_type in {"id", "file"}:
diff --git a/python/packages/ag-ui/tests/ag_ui/test_message_adapters.py b/python/packages/ag-ui/tests/ag_ui/test_message_adapters.py
index d1f90157e6..c78bec3293 100644
--- a/python/packages/ag-ui/tests/ag_ui/test_message_adapters.py
+++ b/python/packages/ag-ui/tests/ag_ui/test_message_adapters.py
@@ -2045,3 +2045,39 @@ def test_parse_multimodal_media_part_unknown_source_value_fallback():
     )
     assert result is not None
     assert "aGVsbG8=" in result.uri  # type: ignore[operator]  # pyrefly: ignore[not-iterable]  # ty: ignore[unsupported-operator]
+
+
+def test_parse_multimodal_media_part_url_value_field():
+    """Source with type='url' reads the URL from the 'value' field per AG-UI spec."""
+    from agent_framework_ag_ui._message_adapters import _parse_multimodal_media_part
+
+    result = _parse_multimodal_media_part(
+        {
+            "type": "document",
+            "source": {
+                "type": "url",
+                "value": "https://example.com/files/document.pdf",
+                "mime_type": "application/pdf",
+            },
+        }
+    )
+    assert result is not None
+    assert result.uri == "https://example.com/files/document.pdf"
+    assert result.media_type == "application/pdf"
+
+
+def test_parse_multimodal_media_part_url_field_backward_compat():
+    """Source with type='url' still supports the non-spec 'url' and 'uri' fields."""
+    from agent_framework_ag_ui._message_adapters import _parse_multimodal_media_part
+
+    from_url = _parse_multimodal_media_part(
+        {"type": "image", "source": {"type": "url", "url": "https://example.com/a.png"}}
+    )
+    assert from_url is not None
+    assert from_url.uri == "https://example.com/a.png"
+
+    from_uri = _parse_multimodal_media_part(
+        {"type": "image", "source": {"type": "uri", "uri": "https://example.com/b.png"}}
+    )
+    assert from_uri is not None
+    assert from_uri.uri == "https://example.com/b.png"