diff --git a/src/blacki/sandbox/config.py b/src/blacki/sandbox/config.py
index e5825e0..0700559 100644
--- a/src/blacki/sandbox/config.py
+++ b/src/blacki/sandbox/config.py
@@ -9,6 +9,8 @@
 
 from pydantic import BaseModel, Field, field_validator
 
+DEFAULT_SANDBOX_IMAGE: Final[str] = "ghcr.io/queryplanner/blacki-sandbox:latest"
+
 
 class SandboxConfig(BaseModel):
     """Configuration for OpenSandbox sandbox operations.
@@ -36,14 +38,16 @@ class SandboxConfig(BaseModel):
     memory_limit: str = Field(default="1Gi", description="Memory limit per sandbox")
     cpu_limit: str = Field(default="0.5", description="CPU limit per sandbox")
     image: str = Field(
-        default="ghcr.io/queryplanner/athena-sandbox:latest",
+        default=DEFAULT_SANDBOX_IMAGE,
         description="Docker image for sandboxes",
     )
     entrypoint: list[str] = Field(
         default=[
             "/bin/sh",
             "-c",
-            "if command -v athena-sandbox-start >/dev/null 2>&1; then "
+            "if command -v blacki-sandbox-start >/dev/null 2>&1; then "
+            "exec blacki-sandbox-start; "
+            "elif command -v athena-sandbox-start >/dev/null 2>&1; then "
             "exec athena-sandbox-start; "
             "elif [ -x /opt/opensandbox/code-interpreter.sh ]; then "
             "exec /opt/opensandbox/code-interpreter.sh; "
@@ -89,7 +93,7 @@ def load_sandbox_config() -> SandboxConfig:
         SANDBOX_TIMEOUT_MINUTES: Sandbox TTL in minutes (default: 30)
         SANDBOX_MEMORY_LIMIT: Memory limit per sandbox (default: 1Gi)
         SANDBOX_CPU_LIMIT: CPU limit per sandbox (default: 0.5)
-        SANDBOX_IMAGE: Docker image for sandboxes (default: the shared
+        SANDBOX_IMAGE: Docker image for sandboxes (default: the Blacki
             Chromium/agent-browser image)
 
     Returns:
@@ -105,9 +109,7 @@ def load_sandbox_config() -> SandboxConfig:
         timeout_minutes=int(os.getenv("SANDBOX_TIMEOUT_MINUTES", "30").strip()),
         memory_limit=os.getenv("SANDBOX_MEMORY_LIMIT", "1Gi").strip(),
         cpu_limit=os.getenv("SANDBOX_CPU_LIMIT", "0.5").strip(),
-        image=os.getenv(
-            "SANDBOX_IMAGE", "ghcr.io/queryplanner/athena-sandbox:latest"
-        ).strip(),
+        image=os.getenv("SANDBOX_IMAGE", DEFAULT_SANDBOX_IMAGE).strip(),
     )
 
 
diff --git a/tests/sandbox/test_config.py b/tests/sandbox/test_config.py
index 6a094b7..fc718e2 100644
--- a/tests/sandbox/test_config.py
+++ b/tests/sandbox/test_config.py
@@ -26,8 +26,9 @@ def test_default_values(self) -> None:
         assert config.timeout_minutes == 30
         assert config.memory_limit == "1Gi"
         assert config.cpu_limit == "0.5"
-        assert config.image == "ghcr.io/queryplanner/athena-sandbox:latest"
+        assert config.image == "ghcr.io/queryplanner/blacki-sandbox:latest"
         entrypoint = config.entrypoint[-1]
+        assert "blacki-sandbox-start" in entrypoint
         assert "athena-sandbox-start" in entrypoint
         assert "/opt/opensandbox/code-interpreter.sh" in entrypoint
 
@@ -89,6 +90,14 @@ def test_timeout_minutes_bounds(self) -> None:
 class TestLoadSandboxConfig:
     """Tests for load_sandbox_config."""
 
+    def test_default_image_without_override(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        monkeypatch.delenv("SANDBOX_IMAGE", raising=False)
+        assert (
+            load_sandbox_config().image == "ghcr.io/queryplanner/blacki-sandbox:latest"
+        )
+
     def test_load_from_environment(self) -> None:
         """Test loading config from environment variables."""
         env = {