diff --git a/python/flydsl/compiler/backends/__init__.py b/python/flydsl/compiler/backends/__init__.py
index 5e67fd61..cca36ff5 100644
--- a/python/flydsl/compiler/backends/__init__.py
+++ b/python/flydsl/compiler/backends/__init__.py
@@ -68,6 +68,10 @@ def get_backend(name: Optional[str] = None, *, arch: str = "") -> BaseBackend:
 
     *name* defaults to ``FLYDSL_COMPILE_BACKEND`` env var (or ``'rocm'``).
     *arch* overrides the auto-detected architecture when non-empty.
+
+    Compile/runtime pairing (``FLYDSL_COMPILE_BACKEND`` vs ``FLYDSL_RUNTIME_KIND``)
+    is validated on the JIT path when a kernel is compiled or loaded for execution
+    (see :func:`flydsl.runtime.device_runtime.get_device_runtime`), not here.
     """
     if name is None:
         name = compile_backend_name()
diff --git a/python/flydsl/compiler/jit_executor.py b/python/flydsl/compiler/jit_executor.py
index 1d3c5ddd..934c0ef7 100644
--- a/python/flydsl/compiler/jit_executor.py
+++ b/python/flydsl/compiler/jit_executor.py
@@ -85,6 +85,11 @@ def _ensure_engine(self):
             if self._engine is not None:
                 return
 
+            # Validate compile backend vs device runtime before loading ExecutionEngine.
+            from ..runtime.device_runtime import get_device_runtime
+
+            get_device_runtime()
+
             with ir.Context() as ctx:
                 ctx.load_all_available_dialects()
                 self._module = ir.Module.parse(self._ir_text)
diff --git a/python/flydsl/compiler/jit_function.py b/python/flydsl/compiler/jit_function.py
index 1be37d85..5b3139ba 100644
--- a/python/flydsl/compiler/jit_function.py
+++ b/python/flydsl/compiler/jit_function.py
@@ -778,6 +778,11 @@ def __call__(self, *args, **kwargs):
 
             compiled_module = MlirCompiler.compile(module, arch=backend.target.arch, func_name=self.func.__name__)
 
+            # Compile/runtime pairing before COMPILE_ONLY return (no ExecutionEngine on that path).
+            from ..runtime.device_runtime import get_device_runtime
+
+            get_device_runtime()
+
             if env.compile.compile_only:
                 print(f"[flydsl] COMPILE_ONLY=1, compilation succeeded (arch={backend.target.arch})")
                 return None
diff --git a/python/flydsl/expr/typing.py b/python/flydsl/expr/typing.py
index 061d4d37..2d09d0c8 100644
--- a/python/flydsl/expr/typing.py
+++ b/python/flydsl/expr/typing.py
@@ -300,6 +300,13 @@ def __fly_values__(self):
 
 
 class Stream:
+    """Opaque async queue handle for kernel launch.
+
+    Values may be ``None`` (default queue), a raw pointer, or a framework stream
+    with a ``cuda_stream`` attribute (e.g. PyTorch); the active
+    :class:`flydsl.runtime.device_runtime.DeviceRuntime` interprets them.
+    """
+
     _is_stream_param = True
 
     def __init__(self, value=None):
diff --git a/python/flydsl/runtime/__init__.py b/python/flydsl/runtime/__init__.py
index 450d0f1d..0ffce4ab 100644
--- a/python/flydsl/runtime/__init__.py
+++ b/python/flydsl/runtime/__init__.py
@@ -1,3 +1,28 @@
 # SPDX-License-Identifier: Apache-2.0
 # Copyright (c) 2025 FlyDSL Project Contributors
 
+"""FlyDSL runtime: device runtime, GPU detection helpers, etc."""
+
+from .device_runtime import (
+    COMPILE_BACKEND_TO_RUNTIME_KIND,
+    Device,
+    DeviceRuntime,
+    Event,
+    RocmDeviceRuntime,
+    ensure_compile_runtime_compatible,
+    get_device_runtime,
+    register_compile_runtime_mapping,
+    register_device_runtime,
+)
+
+__all__ = [
+    "COMPILE_BACKEND_TO_RUNTIME_KIND",
+    "Device",
+    "DeviceRuntime",
+    "Event",
+    "RocmDeviceRuntime",
+    "ensure_compile_runtime_compatible",
+    "get_device_runtime",
+    "register_compile_runtime_mapping",
+    "register_device_runtime",
+]
diff --git a/python/flydsl/runtime/device_runtime/__init__.py b/python/flydsl/runtime/device_runtime/__init__.py
new file mode 100644
index 00000000..c6755c4a
--- /dev/null
+++ b/python/flydsl/runtime/device_runtime/__init__.py
@@ -0,0 +1,148 @@
+# SPDX-License-Identifier: Apache-2.0
+# Copyright (c) 2025 FlyDSL Project Contributors
+
+"""Per-process GPU device runtime.
+
+Exactly one :class:`DeviceRuntime` implementation is active per process.
+It must match the selected compile backend (e.g. ``rocm`` compile backend ↔
+``rocm`` runtime / HIP).
+
+Environment:
+
+* ``FLYDSL_RUNTIME_KIND`` — selects the built-in runtime implementation
+  (default: ``rocm``). Must agree with ``FLYDSL_COMPILE_BACKEND`` via
+  :data:`COMPILE_BACKEND_TO_RUNTIME_KIND` (and optional extension mappings).
+"""
+
+from __future__ import annotations
+
+from typing import Dict, Optional, Type
+
+from ...utils import env
+from .base import Device, DeviceRuntime, Event
+from .rocm import RocmDeviceRuntime
+
+# Compile-backend id -> device-runtime kind (single string namespace).
+COMPILE_BACKEND_TO_RUNTIME_KIND: Dict[str, str] = {
+    "rocm": "rocm",
+}
+
+_EXTRA_MAPPINGS: Dict[str, str] = {}
+
+_builtin_runtimes: Dict[str, Type[DeviceRuntime]] = {
+    "rocm": RocmDeviceRuntime,
+}
+
+_runtime_cls_override: Optional[Type[DeviceRuntime]] = None
+_instance: Optional[DeviceRuntime] = None
+
+
+def register_compile_runtime_mapping(compile_backend: str, runtime_kind: str) -> None:
+    """Map a compile-backend id to a device-runtime *kind*.
+
+    Use when a third-party :func:`flydsl.compiler.backends.register_backend`
+    targets an existing runtime stack (e.g. custom name → ``rocm``).
+    """
+    _EXTRA_MAPPINGS[compile_backend.strip().lower()] = runtime_kind.strip().lower()
+
+
+def register_device_runtime(
+    cls: Type[DeviceRuntime],
+    *,
+    kind: Optional[str] = None,
+    force: bool = False,
+) -> None:
+    """Register a custom :class:`DeviceRuntime` class for the whole process.
+
+    Must be called before the first :func:`get_device_runtime` if replacing the
+    default. Raises if a runtime instance already exists, unless ``force=True``.
+
+    If *kind* is set, the class is also registered under that runtime *kind* for
+    ``FLYDSL_RUNTIME_KIND`` (and should match the compile-backend mapping).
+    """
+    global _runtime_cls_override, _instance
+    if _instance is not None and not force:
+        raise RuntimeError(
+            "Cannot register a device runtime after get_device_runtime() "
+            "has been called (unless force=True)."
+        )
+    if _runtime_cls_override is not None and not force:
+        raise ValueError(
+            "A custom device runtime class is already registered "
+            "(use force=True to replace)."
+        )
+    _runtime_cls_override = cls
+    if kind is not None:
+        _builtin_runtimes[kind.strip().lower()] = cls
+
+
+def _expected_runtime_kind_for_compile_backend(compile_backend_id: str) -> str:
+    key = compile_backend_id.strip().lower()
+    if key in _EXTRA_MAPPINGS:
+        return _EXTRA_MAPPINGS[key]
+    if key in COMPILE_BACKEND_TO_RUNTIME_KIND:
+        return COMPILE_BACKEND_TO_RUNTIME_KIND[key]
+    raise ValueError(
+        f"No device-runtime kind mapped for compile backend {compile_backend_id!r}. "
+        "Register a mapping with register_compile_runtime_mapping()."
+    )
+
+
+def _resolve_runtime_class() -> Type[DeviceRuntime]:
+    if _runtime_cls_override is not None:
+        return _runtime_cls_override
+    kind = (env.runtime.kind or "rocm").strip().lower()
+    cls = _builtin_runtimes.get(kind)
+    if cls is None:
+        known = ", ".join(sorted(_builtin_runtimes)) or "(none)"
+        raise ValueError(
+            f"Unknown FLYDSL_RUNTIME_KIND={kind!r}. Built-in kinds: {known}"
+        )
+    return cls
+
+
+def ensure_compile_runtime_compatible(
+    compile_backend_id: str,
+    *,
+    runtime: Optional[DeviceRuntime] = None,
+) -> None:
+    """Raise if *compile_backend_id* does not match the active runtime kind."""
+    expected = _expected_runtime_kind_for_compile_backend(compile_backend_id)
+    rt = runtime if runtime is not None else get_device_runtime()
+    if rt.kind != expected:
+        raise RuntimeError(
+            f"Compile backend {compile_backend_id!r} requires device runtime kind "
+            f"{expected!r}, but the active runtime is {rt.kind!r}. "
+            f"Align FLYDSL_COMPILE_BACKEND with FLYDSL_RUNTIME_KIND (and extension "
+            f"mappings), or use a matching pair of register_backend / "
+            f"register_device_runtime."
+        )
+
+
+def _active_compile_backend_id() -> str:
+    """Mirror :func:`flydsl.compiler.backends.compile_backend_name` without importing ``compiler``."""
+    return (env.compile.backend or "rocm").lower()
+
+
+def get_device_runtime() -> DeviceRuntime:
+    """Return the single process-wide :class:`DeviceRuntime` instance."""
+    global _instance
+    if _instance is None:
+        cls = _resolve_runtime_class()
+        _instance = cls()
+
+    ensure_compile_runtime_compatible(_active_compile_backend_id(), runtime=_instance)
+    return _instance
+
+
+__all__ = [
+    "COMPILE_BACKEND_TO_RUNTIME_KIND",
+    "Device",
+    "DeviceRuntime",
+    "Event",
+    "RocmDeviceRuntime",
+    "ensure_compile_runtime_compatible",
+    "get_device_runtime",
+    "register_compile_runtime_mapping",
+    "register_device_runtime",
+]
diff --git a/python/flydsl/runtime/device_runtime/base.py b/python/flydsl/runtime/device_runtime/base.py
new file mode 100644
index 00000000..5943776d
--- /dev/null
+++ b/python/flydsl/runtime/device_runtime/base.py
@@ -0,0 +1,47 @@
+# SPDX-License-Identifier: Apache-2.0
+# Copyright (c) 2025 FlyDSL Project Contributors
+
+"""Abstract device runtime : single native GPU stack per process."""
+
+from __future__ import annotations
+
+from abc import ABCMeta, abstractmethod
+from dataclasses import dataclass
+from typing import ClassVar
+
+
+@dataclass(frozen=True)
+class Device:
+    """Logical GPU device (ordinal only in v1; capabilities may extend later)."""
+
+    ordinal: int = 0
+    """Device index for the active runtime (e.g. HIP device id)."""
+
+
+class DeviceRuntime(metaclass=ABCMeta):
+    """Vendor-neutral runtime: one implementation per process (HIP, CUDA, …).
+
+    Stream and Event handles stay opaque at the Python/C boundary; concrete
+    APIs live in native glue (e.g. ROCm wrappers).
+    """
+
+    kind: ClassVar[str]
+    """Stable runtime identifier (e.g. ``\"rocm\"`` for HIP/ROCm)."""
+
+    @abstractmethod
+    def device_count(self) -> int:
+        """Number of visible devices for this runtime."""
+
+    def default_device(self) -> Device:
+        """Default device for launch when none is specified."""
+        return Device(ordinal=0)
+
+
+class Event:
+    """Placeholder for future opaque event handles.
+
+    Kernel launch paths may synchronize via streams; explicit events can be
+    added without changing the compile-backend layer.
+    """
+
+    __slots__ = ()
diff --git a/python/flydsl/runtime/device_runtime/rocm.py b/python/flydsl/runtime/device_runtime/rocm.py
new file mode 100644
index 00000000..2de9eda4
--- /dev/null
+++ b/python/flydsl/runtime/device_runtime/rocm.py
@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: Apache-2.0
+# Copyright (c) 2025 FlyDSL Project Contributors
+
+"""ROCm / HIP device runtime (default FlyDSL GPU stack)."""
+
+from __future__ import annotations
+
+from typing import ClassVar, Optional
+
+from .base import DeviceRuntime
+
+
+class RocmDeviceRuntime(DeviceRuntime):
+    """HIP-based runtime; matches compile backend ``rocm``.
+
+    ``device_count()`` reports 0 when no GPU is visible to PyTorch (no fake device).
+    """
+
+    kind: ClassVar[str] = "rocm"
+
+    def __init__(self) -> None:
+        self._torch_device_count: Optional[int] = None
+
+    def _lazy_device_count(self) -> int:
+        if self._torch_device_count is not None:
+            return self._torch_device_count
+        try:
+            import torch
+
+            # ROCm builds still use the torch.cuda Python API for device visibility.
+            if torch.cuda.is_available():
+                n = int(torch.cuda.device_count())
+            else:
+                n = 0
+        except Exception:
+            n = 0
+        self._torch_device_count = n
+        return self._torch_device_count
+
+    def device_count(self) -> int:
+        return self._lazy_device_count()
diff --git a/python/flydsl/utils/env.py b/python/flydsl/utils/env.py
index fefe7997..9689a7e8 100644
--- a/python/flydsl/utils/env.py
+++ b/python/flydsl/utils/env.py
@@ -255,6 +255,10 @@ class RuntimeEnvManager(EnvManager):
 
     env_prefix = "RUNTIME"
 
+    kind = OptStr(
+        "rocm",
+        description="Device runtime kind (must match FLYDSL_COMPILE_BACKEND; e.g. rocm for HIP)",
+    )
     cache_dir = OptStr(str(Path.home() / ".flydsl" / "cache"), description="Directory for caching compiled kernels")
     enable_cache = OptBool(True, description="Enable kernel caching")
 
diff --git a/tests/unit/test_device_runtime.py b/tests/unit/test_device_runtime.py
new file mode 100644
index 00000000..edebe0f6
--- /dev/null
+++ b/tests/unit/test_device_runtime.py
@@ -0,0 +1,56 @@
+# SPDX-License-Identifier: Apache-2.0
+# Copyright (c) 2025 FlyDSL Project Contributors
+
+"""device runtime registry and compile-backend pairing."""
+
+import pytest
+
+import flydsl.runtime.device_runtime as dr
+
+
+@pytest.fixture(autouse=True)
+def _reset_device_runtime_singleton():
+    """Each test starts without a cached DeviceRuntime instance."""
+    dr._instance = None
+    dr._runtime_cls_override = None
+    dr._EXTRA_MAPPINGS.clear()
+    yield
+    dr._instance = None
+    dr._runtime_cls_override = None
+    dr._EXTRA_MAPPINGS.clear()
+
+
+class _FakeCudaRuntime(dr.DeviceRuntime):
+    kind = "cuda"
+
+    def device_count(self) -> int:
+        return 1
+
+
+def test_rocm_runtime_kind_matches_compile_backend(monkeypatch):
+    monkeypatch.delenv("FLYDSL_RUNTIME_KIND", raising=False)
+    monkeypatch.setenv("FLYDSL_COMPILE_BACKEND", "rocm")
+    rt = dr.get_device_runtime()
+    assert rt.kind == "rocm"
+    dr.ensure_compile_runtime_compatible("rocm", runtime=rt)
+
+
+def test_ensure_mismatch_raises():
+    bad = _FakeCudaRuntime()
+    with pytest.raises(RuntimeError, match="requires device runtime kind"):
+        dr.ensure_compile_runtime_compatible("rocm", runtime=bad)
+
+
+def test_unknown_runtime_kind_env(monkeypatch):
+    monkeypatch.setenv("FLYDSL_RUNTIME_KIND", "not_a_real_kind")
+    monkeypatch.setenv("FLYDSL_COMPILE_BACKEND", "rocm")
+    with pytest.raises(ValueError, match="Unknown FLYDSL_RUNTIME_KIND"):
+        dr.get_device_runtime()
+
+
+def test_register_compile_runtime_mapping():
+    dr.register_compile_runtime_mapping("foo", "rocm")
+    try:
+        dr.ensure_compile_runtime_compatible("foo", runtime=dr.RocmDeviceRuntime())
+    finally:
+        dr._EXTRA_MAPPINGS.pop("foo", None)