diff --git a/CONFIG_REFERENCE.md b/CONFIG_REFERENCE.md
index f05d64db..aa8703d7 100644
--- a/CONFIG_REFERENCE.md
+++ b/CONFIG_REFERENCE.md
@@ -184,6 +184,7 @@ Accepted keys:
   - `trace` — mapping. Optional. Use with callable targets that emit OpenTelemetry spans.
     - `backend` — string. Default: `phoenix`.
     - `group_by` — string. Customer preview supports `session.id`.
+    - `project_name` — string. Optional. Routes spans to a named Phoenix project instead of `"default"`. Sets `PHOENIX_PROJECT_NAME` before importing the target module.
   - `tools` — mapping. Optional. Allowed only when `target.model` is set.
     - `module` — string. Use a Python tool backend module.
     - `toolset` — string. Use a toolset file.
@@ -206,6 +207,7 @@ pipeline:
       trace:
         backend: phoenix
         group_by: session.id
+        project_name: travel-planner-eval
     auditor:
       model:
         name: azure/gpt-5.4-mini
diff --git a/p2m/core/config_model.py b/p2m/core/config_model.py
index 921e03e9..9865511f 100644
--- a/p2m/core/config_model.py
+++ b/p2m/core/config_model.py
@@ -93,8 +93,10 @@ def __post_init__(self) -> None:
 class TraceConfig:
     backend: str = "phoenix"
     group_by: str = "session.id"
+    project_name: str | None = None
 
     def __post_init__(self) -> None:
+        self.project_name = _normalize_optional_string(self.project_name)
         if self.group_by not in VALID_TRACE_GROUP_BY:
             raise ValueError(
                 f"trace.group_by must be 'session.id'. "
diff --git a/p2m/core/otel_session.py b/p2m/core/otel_session.py
index 178c6221..281db1a0 100644
--- a/p2m/core/otel_session.py
+++ b/p2m/core/otel_session.py
@@ -69,6 +69,7 @@ def __init__(
         exporter: TraceExporter | None = None,
         collector: SpanCollector | None = None,
         group_by: str = "session.id",
+        project_name: str | None = None,
         system_prompt: str | None = None,
         message_timeout_s: float | None = None,
         max_events_per_turn: int = 50,
@@ -77,6 +78,7 @@ def __init__(
         self._callable_ref = callable_ref
         self._collector = collector
         self._group_by = group_by
+        self._project_name = project_name
         self._system_prompt = system_prompt
         self._message_timeout_s = message_timeout_s
         self._max_events_per_turn = max_events_per_turn
@@ -108,9 +110,21 @@ def session_metadata(self) -> dict[str, Any] | None:
 
     async def open(self) -> None:
         import io
+        import os
         import sys
 
         module_path, func_name = self._callable_ref.rsplit(":", 1)
+
+        # Set Phoenix project name before importing the target module.
+        # Phoenix's register() reads PHOENIX_PROJECT_NAME from the
+        # environment when no explicit project_name is passed. By setting
+        # it here we route spans to a named project without interfering
+        # with the target's register() call or the set-once TracerProvider
+        # guard.
+        _prev_project_name = os.environ.get("PHOENIX_PROJECT_NAME")
+        if self._project_name:
+            os.environ["PHOENIX_PROJECT_NAME"] = self._project_name
+
         # Suppress Phoenix/OTel banner output during module import.
         # Phoenix's register(verbose=True) prints a multi-line banner to
         # stdout when the target module calls register() at import time.
@@ -120,6 +134,12 @@ async def open(self) -> None:
             mod = importlib.import_module(module_path)
         finally:
             sys.stdout = _orig_stdout
+            # Restore original env var state to avoid side effects.
+            if self._project_name:
+                if _prev_project_name is None:
+                    os.environ.pop("PHOENIX_PROJECT_NAME", None)
+                else:
+                    os.environ["PHOENIX_PROJECT_NAME"] = _prev_project_name
         self._callable = getattr(mod, func_name)
         sig = inspect.signature(self._callable)
         self._supports_history = "history" in sig.parameters
diff --git a/p2m/stages/rollout.py b/p2m/stages/rollout.py
index fe1a5650..03023ebc 100644
--- a/p2m/stages/rollout.py
+++ b/p2m/stages/rollout.py
@@ -475,6 +475,7 @@ def _build_target_session(
                 system_prompt=target.system_prompt,
                 message_timeout_s=rollout.tool_timeout_s,
                 group_by=target.trace.group_by,
+                project_name=target.trace.project_name,
                 live_otel=True,
             )
         return CallableSession(
diff --git a/tests/test_framework_agnostic.py b/tests/test_framework_agnostic.py
index 900fec4e..a4be4840 100644
--- a/tests/test_framework_agnostic.py
+++ b/tests/test_framework_agnostic.py
@@ -615,6 +615,69 @@ async def _run():
         finally:
             del sys.modules["_test_otel_target"]
 
+    def test_project_name_sets_env_var(self):
+        """project_name should set PHOENIX_PROJECT_NAME before module import."""
+        from p2m.core.otel_session import OTelTracedSession
+
+        import os
+        import sys
+        import types
+
+        captured_env = {}
+        mod = types.ModuleType("_test_otel_projname")
+        _original_init = mod.__dict__.get("__init__")
+
+        # Record the env var value at module import time
+        captured_env["at_import"] = os.environ.get("PHOENIX_PROJECT_NAME")
+        mod.target = lambda msg: "ok"
+
+        # We need the env capture to happen at import time.
+        # Create a fresh module that captures env on import.
+        code = (
+            "import os\n"
+            "CAPTURED_PROJECT = os.environ.get('PHOENIX_PROJECT_NAME')\n"
+            "def target(msg): return 'ok'\n"
+        )
+        mod = types.ModuleType("_test_otel_projname")
+        exec(code, mod.__dict__)
+        # Don't register yet — we'll let open() do the import
+
+        # Remove from sys.modules so open() triggers a fresh import
+        sys.modules.pop("_test_otel_projname", None)
+
+        # Write a temp module file so importlib can find it
+        import tempfile
+        tmpdir = tempfile.mkdtemp()
+        modpath = os.path.join(tmpdir, "_test_otel_projname.py")
+        with open(modpath, "w") as f:
+            f.write(code)
+
+        sys.path.insert(0, tmpdir)
+        try:
+            original_val = os.environ.get("PHOENIX_PROJECT_NAME")
+            session = OTelTracedSession(
+                callable_ref="_test_otel_projname:target",
+                project_name="my-test-project",
+            )
+
+            async def _run():
+                await session.open()
+                await session.close()
+
+            asyncio.run(_run())
+
+            # Verify the module captured the env var at import time
+            imported = sys.modules["_test_otel_projname"]
+            self.assertEqual(imported.CAPTURED_PROJECT, "my-test-project")
+
+            # Verify env var is restored after open()
+            self.assertEqual(os.environ.get("PHOENIX_PROJECT_NAME"), original_val)
+        finally:
+            sys.path.remove(tmpdir)
+            sys.modules.pop("_test_otel_projname", None)
+            import shutil
+            shutil.rmtree(tmpdir, ignore_errors=True)
+
     def test_run_turn_with_history(self):
         """OTelTracedSession should detect and pass history parameter."""
         from p2m.core.otel_session import OTelTracedSession