diff --git a/bot_bottle/agent_provider.py b/bot_bottle/agent_provider.py
index f455d68..9d65154 100644
--- a/bot_bottle/agent_provider.py
+++ b/bot_bottle/agent_provider.py
@@ -45,7 +45,12 @@ PROVIDER_TEMPLATES = frozenset({PROVIDER_CLAUDE, PROVIDER_CODEX, PROVIDER_PI})
 # forward_host_credentials is enabled. Pipelock must pass these through
 # (no TLS MITM) or its header DLP blocks the injected JWT.
 CODEX_HOST_CREDENTIAL_HOSTS = ("api.openai.com", "chatgpt.com")
-PromptMode = Literal["append_file", "read_prompt_file", "print_read_prompt_file"]
+PromptMode = Literal[
+    "append_file",
+    "read_prompt_file",
+    "print_read_prompt_file",
+    "append_system_prompt",
+]
 
 
 @dataclass(frozen=True)
@@ -381,4 +386,6 @@ def prompt_args(
         return [f"Read and follow the instructions in {prompt_path}."]
     if prompt_mode == "print_read_prompt_file":
         return ["-p", f"Read and follow the instructions in {prompt_path}."]
+    if prompt_mode == "append_system_prompt":
+        return ["--append-system-prompt", prompt_path]
     raise ValueError(f"unknown provider prompt mode: {prompt_mode}")
diff --git a/bot_bottle/contrib/pi/agent_provider.py b/bot_bottle/contrib/pi/agent_provider.py
index c823a78..b2a1453 100644
--- a/bot_bottle/contrib/pi/agent_provider.py
+++ b/bot_bottle/contrib/pi/agent_provider.py
@@ -111,7 +111,7 @@ _RUNTIME = AgentProviderRuntime(
     template="pi",
     command="pi",
     image="bot-bottle-pi:latest",
-    prompt_mode="print_read_prompt_file",
+    prompt_mode="append_system_prompt",
     bypass_args=(),
     resume_args=(),
     remote_control_args=(),
diff --git a/docs/prds/0058-pi-agent-provider.md b/docs/prds/0058-pi-agent-provider.md
index 83a00fb..7191a77 100644
--- a/docs/prds/0058-pi-agent-provider.md
+++ b/docs/prds/0058-pi-agent-provider.md
@@ -93,7 +93,7 @@ endpoint.
 The Pi runtime uses:
 
 - `command="pi"`
-- `prompt_mode="read_prompt_file"`
+- `prompt_mode="append_system_prompt"`
 - `image="bot-bottle-pi:latest"`
 - `bypass_args=()`
 - `resume_args=()`
diff --git a/tests/unit/test_agent_provider.py b/tests/unit/test_agent_provider.py
index 3a3993e..57bfc55 100644
--- a/tests/unit/test_agent_provider.py
+++ b/tests/unit/test_agent_provider.py
@@ -273,7 +273,7 @@ class TestAgentProviderRuntime(unittest.TestCase):
             models = json.loads(Path(tmp, "pi-models.json").read_text())
         self.assertEqual("pi", plan.template)
         self.assertEqual("pi", plan.command)
-        self.assertEqual("print_read_prompt_file", plan.prompt_mode)
+        self.assertEqual("append_system_prompt", plan.prompt_mode)
         self.assertEqual("/tmp/Dockerfile.pi", plan.dockerfile)
         self.assertEqual("bot-bottle-pi:latest", plan.image)
         self.assertEqual(
@@ -354,10 +354,10 @@ class TestAgentProviderRuntime(unittest.TestCase):
         self.assertNotIn("OPENROUTER_API_KEY", plan.guest_env)
         self.assertTrue(provider["compat"]["supportsReasoningEffort"])
 
-    def test_pi_prompt_mode_uses_print_flag(self):
+    def test_pi_prompt_mode_appends_system_prompt_interactively(self):
         self.assertEqual(
-            ["-p", "Read and follow the instructions in /home/node/.bot-bottle-prompt.txt."],
-            prompt_args("print_read_prompt_file", "/home/node/.bot-bottle-prompt.txt"),
+            ["--append-system-prompt", "/home/node/.bot-bottle-prompt.txt"],
+            prompt_args("append_system_prompt", "/home/node/.bot-bottle-prompt.txt"),
         )
 
 
diff --git a/tests/unit/test_contrib_pi_provider.py b/tests/unit/test_contrib_pi_provider.py
index 143f216..17d3a18 100644
--- a/tests/unit/test_contrib_pi_provider.py
+++ b/tests/unit/test_contrib_pi_provider.py
@@ -77,7 +77,7 @@ def _plan(
         supervise_plan=None,
         use_runsc=False,
         agent_provision=agent_provision or AgentProvisionPlan(
-            template="pi", command="pi", prompt_mode="print_read_prompt_file",
+            template="pi", command="pi", prompt_mode="append_system_prompt",
             image="bot-bottle-pi:latest", dockerfile="",
             guest_home="/home/node",
             instance_name="bot-bottle-demo-abc12",
@@ -144,7 +144,7 @@ class TestPiProvisionSkills(unittest.TestCase):
 class TestPiProvision(unittest.TestCase):
     def test_creates_dir_and_copies_models_config(self):
         provision = AgentProvisionPlan(
-            template="pi", command="pi", prompt_mode="print_read_prompt_file",
+            template="pi", command="pi", prompt_mode="append_system_prompt",
             image="", dockerfile="", guest_home="/home/node",
             instance_name="bot-bottle-demo-abc12",
             prompt_file=Path("/tmp/prompt.txt"),
@@ -172,7 +172,7 @@ class TestPiProvision(unittest.TestCase):
 
     def test_dies_when_dir_creation_fails(self):
         provision = AgentProvisionPlan(
-            template="pi", command="pi", prompt_mode="print_read_prompt_file",
+            template="pi", command="pi", prompt_mode="append_system_prompt",
             image="", dockerfile="", guest_home="/home/node",
             instance_name="bot-bottle-demo-abc12",
             prompt_file=Path("/tmp/prompt.txt"),
diff --git a/tests/unit/test_docker_bottle.py b/tests/unit/test_docker_bottle.py
index 72a3644..dfbc3da 100644
--- a/tests/unit/test_docker_bottle.py
+++ b/tests/unit/test_docker_bottle.py
@@ -31,6 +31,16 @@ def _codex_bottle(prompt_path: str | None = None) -> DockerBottle:
     )
 
 
+def _pi_bottle(prompt_path: str | None = None) -> DockerBottle:
+    return DockerBottle(
+        container="bot-bottle-dev-abc",
+        teardown=lambda: None,
+        prompt_path_in_container=prompt_path,
+        agent_command="pi",
+        agent_prompt_mode="append_system_prompt",
+    )
+
+
 class TestClaudeArgv(unittest.TestCase):
     def test_minimal_argv_no_prompt(self):
         argv = _bottle().agent_argv([])
@@ -117,6 +127,15 @@ class TestClaudeArgv(unittest.TestCase):
             argv,
         )
 
+    def test_pi_provider_appends_system_prompt_without_print_mode(self):
+        argv = _pi_bottle("/home/node/.bot-bottle-prompt.txt").agent_argv([])
+        self.assertEqual(
+            ["docker", "exec", "-it", "bot-bottle-dev-abc", "pi",
+             "--append-system-prompt", "/home/node/.bot-bottle-prompt.txt"],
+            argv,
+        )
+        self.assertNotIn("-p", argv)
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/unit/test_smolmachines_bottle.py b/tests/unit/test_smolmachines_bottle.py
index 0ad99bc..9446348 100644
--- a/tests/unit/test_smolmachines_bottle.py
+++ b/tests/unit/test_smolmachines_bottle.py
@@ -28,6 +28,15 @@ def _bottle(prompt_path: str | None = None, **env: str) -> SmolmachinesBottle:
     )
 
 
+def _pi_bottle(prompt_path: str | None = None) -> SmolmachinesBottle:
+    return SmolmachinesBottle(
+        "bot-bottle-dev-abc",
+        prompt_path=prompt_path,
+        agent_command="pi",
+        agent_prompt_mode="append_system_prompt",
+    )
+
+
 def _unwrap(argv: list[str]) -> list[str]:
     """Strip the pty_resize wrapper from the front of a TTY-mode
     argv, return the inner smolvm argv. Mirrors what the kernel
@@ -122,6 +131,16 @@ class TestClaudeArgvWrapped(unittest.TestCase):
             argv[agent_idx - 7:agent_idx - 2],
         )
 
+    def test_pi_provider_appends_system_prompt_without_print_mode(self):
+        argv = _unwrap(
+            _pi_bottle("/home/node/.bot-bottle-prompt.txt").agent_argv([])
+        )
+        self.assertEqual(
+            ["pi", "--append-system-prompt", "/home/node/.bot-bottle-prompt.txt"],
+            argv[argv.index("pi"):],
+        )
+        self.assertNotIn("-p", argv)
+
 
 class TestClaudeArgvNoTTY(unittest.TestCase):
     """`tty=False` paths skip the pty_resize wrapper — there's no