diff --git a/config/ci.yaml b/config/ci.yaml
new file mode 100644
index 0000000..38e00c9
--- /dev/null
+++ b/config/ci.yaml
@@ -0,0 +1 @@
+env: ci
diff --git a/config/jetson.yaml b/config/jetson.yaml
new file mode 100644
index 0000000..824e9cb
--- /dev/null
+++ b/config/jetson.yaml
@@ -0,0 +1 @@
+env: jetson
diff --git a/config/sitl.yaml b/config/sitl.yaml
new file mode 100644
index 0000000..15801a3
--- /dev/null
+++ b/config/sitl.yaml
@@ -0,0 +1 @@
+env: sitl
diff --git a/config/x86_dev.yaml b/config/x86_dev.yaml
new file mode 100644
index 0000000..1d411a9
--- /dev/null
+++ b/config/x86_dev.yaml
@@ -0,0 +1 @@
+env: x86_dev
diff --git a/pyproject.toml b/pyproject.toml
index 49b7e33..221a019 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -19,6 +19,7 @@ dependencies = [
     "opencv-python-headless>=4.9,<4.11",  # 4.11+ requires numpy>=2.0 (incompatible with GTSAM)
     "gtsam>=4.3a0",
     "pymavlink>=2.4",
+    "pyyaml>=6.0",
 ]
 
 [project.optional-dependencies]
diff --git a/src/gps_denied/config.py b/src/gps_denied/config.py
index 678889f..e5e5741 100644
--- a/src/gps_denied/config.py
+++ b/src/gps_denied/config.py
@@ -3,9 +3,10 @@
 from __future__ import annotations
 
 from pathlib import Path
+from typing import Literal
 
 from pydantic import Field
-from pydantic_settings import BaseSettings, SettingsConfigDict
+from pydantic_settings import BaseSettings, SettingsConfigDict, YamlConfigSettingsSource
 
 
 class DatabaseConfig(BaseSettings):
@@ -162,6 +163,8 @@ class AppSettings(BaseSettings):
         extra="ignore",
     )
 
+    env: Literal["jetson", "x86_dev", "ci", "sitl"] = "x86_dev"
+
     db: DatabaseConfig = Field(default_factory=DatabaseConfig)
     api: APIConfig = Field(default_factory=APIConfig)
     tiles: TileProviderConfig = Field(default_factory=TileProviderConfig)
@@ -174,6 +177,36 @@ class AppSettings(BaseSettings):
     satellite: SatelliteConfig = Field(default_factory=SatelliteConfig)
     eskf: ESKFSettings = Field(default_factory=ESKFSettings)
 
+    @classmethod
+    def settings_customise_sources(cls, settings_cls, **kwargs):
+        """Load YAML overlay from config/{env}.yaml when present."""
+        import os
+        import yaml
+
+        init_kwargs = kwargs.get("init_settings")
+        env_settings = kwargs.get("env_settings")
+        dotenv = kwargs.get("dotenv_settings")
+        file_secret = kwargs.get("file_secret_settings")
+
+        # Determine which env we're in (check ENV env-var before loading YAML)
+        current_env = os.environ.get("ENV", "x86_dev")
+        yaml_path = Path(f"config/{current_env}.yaml")
+
+        yaml_source = None
+        if yaml_path.exists():
+            try:
+                yaml_source = YamlConfigSettingsSource(settings_cls, yaml_file=yaml_path)
+            except Exception:
+                yaml_source = None
+
+        sources = [s for s in [init_kwargs, env_settings, dotenv, file_secret] if s is not None]
+        if yaml_source is not None:
+            sources.append(yaml_source)
+        return tuple(sources)
+
+
+# Alias for external consumers that expect RuntimeConfig
+RuntimeConfig = AppSettings
 
 _settings: AppSettings | None = None