diff --git a/src/agentex/lib/core/tracing/processors/sgp_tracing_processor.py b/src/agentex/lib/core/tracing/processors/sgp_tracing_processor.py
index 6d186de5f..81a2e1780 100644
--- a/src/agentex/lib/core/tracing/processors/sgp_tracing_processor.py
+++ b/src/agentex/lib/core/tracing/processors/sgp_tracing_processor.py
@@ -54,11 +54,30 @@ def _get_span_type(span: Span) -> str:
     return "STANDALONE"
 
 
+def _active_otel_trace_id() -> str | None:
+    """Active OpenTelemetry/W3C trace id as 32-char hex, or None when OTel is absent or no span is recording."""
+    try:
+        from opentelemetry import trace as otel_trace
+    except ImportError:
+        return None
+    context = otel_trace.get_current_span().get_span_context()
+    if not context.is_valid:
+        return None
+    return format(context.trace_id, "032x")
+
+
+def _resolve_trace_id(agentex_trace_id: str) -> str:
+    """Prefer the ambient W3C/OTel trace id so agent spans share the request's observability trace, else keep agentex's own id."""
+    return _active_otel_trace_id() or agentex_trace_id
+
+
 def _add_source_to_span(span: Span, env_vars: EnvironmentVariables) -> None:
     if span.data is None:
         span.data = {}
     if isinstance(span.data, dict):
         span.data["__source__"] = "agentex"
+        # Preserve agentex's own id so the task linkage survives when the SGP trace_id adopts the W3C id.
+        span.data["__agentex_trace_id__"] = span.trace_id
         if env_vars.ACP_TYPE is not None:
             span.data["__acp_type__"] = env_vars.ACP_TYPE
         if env_vars.AGENT_NAME is not None:
@@ -77,7 +96,7 @@ def _build_sgp_span(span: Span, env_vars: EnvironmentVariables) -> SGPSpan:
             span_type=_get_span_type(span),
             span_id=span.id,
             parent_id=span.parent_id,
-            trace_id=span.trace_id,
+            trace_id=_resolve_trace_id(span.trace_id),
             input=span.input,
             output=span.output,
             metadata=span.data,
diff --git a/tests/lib/core/tracing/processors/test_sgp_tracing_processor.py b/tests/lib/core/tracing/processors/test_sgp_tracing_processor.py
index dc8bab127..a259cbda0 100644
--- a/tests/lib/core/tracing/processors/test_sgp_tracing_processor.py
+++ b/tests/lib/core/tracing/processors/test_sgp_tracing_processor.py
@@ -494,3 +494,66 @@ def test_falsy_values_restore_span_start(self, monkeypatch, val):
     def test_other_values_keep_skip_enabled(self, monkeypatch, val):
         monkeypatch.setenv("AGENTEX_TRACING_SKIP_SPAN_START", val)
         assert self._fn()() is True
+
+
+class TestResolveTraceId:
+    def _mod(self):
+        import agentex.lib.core.tracing.processors.sgp_tracing_processor as m
+
+        return m
+
+    def test_prefers_active_otel_trace_id(self, monkeypatch):
+        m = self._mod()
+        monkeypatch.setattr(m, "_active_otel_trace_id", lambda: "4bf92f3577b34da6a3ce929d0e0e4736")
+        assert m._resolve_trace_id("task-123") == "4bf92f3577b34da6a3ce929d0e0e4736"
+
+    def test_falls_back_to_agentex_id_without_otel(self, monkeypatch):
+        m = self._mod()
+        monkeypatch.setattr(m, "_active_otel_trace_id", lambda: None)
+        assert m._resolve_trace_id("task-123") == "task-123"
+
+    def test_active_otel_trace_id_none_without_span(self):
+        pytest.importorskip("opentelemetry")
+        assert self._mod()._active_otel_trace_id() is None
+
+    def test_active_otel_trace_id_returns_w3c_hex(self):
+        otel_trace = pytest.importorskip("opentelemetry.trace")
+        otel_context = pytest.importorskip("opentelemetry.context")
+
+        span_context = otel_trace.SpanContext(
+            trace_id=0x4BF92F3577B34DA6A3CE929D0E0E4736,
+            span_id=0x00F067AA0BA902B7,
+            is_remote=False,
+            trace_flags=otel_trace.TraceFlags(otel_trace.TraceFlags.SAMPLED),
+        )
+        token = otel_context.attach(otel_trace.set_span_in_context(otel_trace.NonRecordingSpan(span_context)))
+        try:
+            resolved = self._mod()._active_otel_trace_id()
+        finally:
+            otel_context.detach(token)
+        assert resolved == "4bf92f3577b34da6a3ce929d0e0e4736"
+
+
+class TestBuildSgpSpanTraceId:
+    def _build(self, monkeypatch, otel_id):
+        import agentex.lib.core.tracing.processors.sgp_tracing_processor as m
+
+        monkeypatch.setattr(m, "_active_otel_trace_id", lambda: otel_id)
+        captured = {}
+        monkeypatch.setattr(m, "create_span", lambda **kw: captured.update(kw) or _make_mock_sgp_span())
+        env = MagicMock(ACP_TYPE=None, AGENT_NAME=None, AGENT_ID=None)
+        span = _make_span()
+        m._build_sgp_span(span, env)
+        return captured, span
+
+    def test_adopts_otel_trace_id_and_preserves_agentex_id(self, monkeypatch):
+        captured, span = self._build(monkeypatch, "4bf92f3577b34da6a3ce929d0e0e4736")
+        assert captured["trace_id"] == "4bf92f3577b34da6a3ce929d0e0e4736"
+        assert isinstance(span.data, dict)
+        assert span.data["__agentex_trace_id__"] == "trace-1"
+
+    def test_keeps_agentex_trace_id_without_otel(self, monkeypatch):
+        captured, span = self._build(monkeypatch, None)
+        assert captured["trace_id"] == "trace-1"
+        assert isinstance(span.data, dict)
+        assert span.data["__agentex_trace_id__"] == "trace-1"