diff --git a/headroom/proxy/handlers/streaming.py b/headroom/proxy/handlers/streaming.py
index 7581b420b..eb0b4d29d 100644
--- a/headroom/proxy/handlers/streaming.py
+++ b/headroom/proxy/handlers/streaming.py
@@ -544,10 +544,15 @@ class StreamingMixin:
                         "data": block.get("data", ""),
                     },
                 }
+            elif block.get("type") == "server_tool_use":
+                block_start = {
+                    "type": "content_block_start",
+                    "index": idx,
+                    "content_block": block,
+                }
             else:
                 raise ValueError(
-                    f"Unsupported Anthropic content block type for SSE conversion: "
-                    f"{block.get('type')!r}"
+                    f"Unsupported Anthropic content block type for SSE conversion: {block.get('type')!r}"
                 )
 
             events.append(
diff --git a/tests/test_sse_thinking_blocks.py b/tests/test_sse_thinking_blocks.py
index 762bf2c58..5ed2abd38 100644
--- a/tests/test_sse_thinking_blocks.py
+++ b/tests/test_sse_thinking_blocks.py
@@ -186,6 +186,35 @@ def test_redacted_thinking_data_preserved() -> None:
     assert block["data"] == redacted_blob
 
 
+def test_response_to_sse_preserves_server_tool_use_blocks() -> None:
+    parser = _Parser()
+    response = {
+        "id": "msg_1",
+        "model": "claude-opus-4",
+        "role": "assistant",
+        "content": [
+            {
+                "type": "server_tool_use",
+                "id": "srv_1",
+                "name": "web_search",
+                "input": {"query": "headroom"},
+            }
+        ],
+        "stop_reason": "end_turn",
+        "usage": {"output_tokens": 1},
+    }
+
+    sse_events = b"".join(parser._response_to_sse(response, "anthropic")).decode("utf-8")
+
+    assert '"type": "content_block_start"' in sse_events
+    assert '"type": "server_tool_use"' in sse_events
+    assert '"name": "web_search"' in sse_events
+
+    round_tripped = parser._parse_sse_to_response(sse_events, "anthropic")
+    assert round_tripped is not None
+    assert round_tripped["content"][0]["type"] == "server_tool_use"
+
+
 def test_response_to_sse_preserves_thinking_redacted_and_citations() -> None:
     parser = _Parser()
     redacted_blob = "ENC:" + ("y" * 200)