diff --git a/cascadeflow/providers/__init__.py b/cascadeflow/providers/__init__.py
index dd70def8..8354d190 100644
--- a/cascadeflow/providers/__init__.py
+++ b/cascadeflow/providers/__init__.py
@@ -18,6 +18,7 @@
 
 _LAZY_PROVIDERS: dict[str, str] = {
     "AnthropicProvider": ".anthropic",
+    "AtlasCloudProvider": ".atlascloud",
     "DeepSeekProvider": ".deepseek",
     "GroqProvider": ".groq",
     "HuggingFaceProvider": ".huggingface",
@@ -57,6 +58,7 @@ def _build_provider_registry() -> dict:
     registry = {}
     _name_to_key = {
         "OpenAIProvider": "openai",
+        "AtlasCloudProvider": "atlascloud",
         "AnthropicProvider": "anthropic",
         "OllamaProvider": "ollama",
         "GroqProvider": "groq",
@@ -137,6 +139,7 @@ def get_available_providers() -> dict[str, BaseProvider]:
     "ModelResponse",
     "PROVIDER_CAPABILITIES",
     "OpenAIProvider",
+    "AtlasCloudProvider",
     "AnthropicProvider",
     "OllamaProvider",
     "GroqProvider",
diff --git a/cascadeflow/providers/atlascloud.py b/cascadeflow/providers/atlascloud.py
new file mode 100644
index 00000000..d320b73a
--- /dev/null
+++ b/cascadeflow/providers/atlascloud.py
@@ -0,0 +1,53 @@
+"""Atlas Cloud provider implementation.
+
+Atlas Cloud exposes an OpenAI-compatible chat completions API, so the provider
+reuses the OpenAI provider implementation with Atlas-specific defaults.
+
+Environment Variables:
+    ATLASCLOUD_API_KEY: Your Atlas Cloud API key
+
+Models:
+    - qwen/qwen3.5-flash: Fast default chat model
+    - deepseek-ai/deepseek-v4-pro: Reasoning-capable chat model
+"""
+
+import os
+from typing import Optional
+
+from .openai import OpenAIProvider
+
+
+class AtlasCloudProvider(OpenAIProvider):
+    """Atlas Cloud provider using the OpenAI-compatible API."""
+
+    BASE_URL = "https://api.atlascloud.ai/v1"
+
+    def __init__(
+        self,
+        api_key: Optional[str] = None,
+        base_url: Optional[str] = None,
+        **kwargs,
+    ):
+        """
+        Initialize Atlas Cloud provider.
+
+        Args:
+            api_key: Atlas Cloud API key (defaults to ATLASCLOUD_API_KEY env var)
+            base_url: Custom base URL (defaults to Atlas Cloud API)
+            **kwargs: Additional OpenAI provider options
+        """
+        atlascloud_api_key = api_key or os.getenv("ATLASCLOUD_API_KEY")
+
+        if not atlascloud_api_key:
+            raise ValueError(
+                "Atlas Cloud API key not found. "
+                "Set ATLASCLOUD_API_KEY environment variable or pass api_key parameter."
+            )
+
+        super().__init__(api_key=atlascloud_api_key, **kwargs)
+        self.base_url = base_url or self.BASE_URL
+
+    @property
+    def name(self) -> str:
+        """Provider name."""
+        return "atlascloud"
diff --git a/cascadeflow/providers/base.py b/cascadeflow/providers/base.py
index f133db14..80458fee 100644
--- a/cascadeflow/providers/base.py
+++ b/cascadeflow/providers/base.py
@@ -947,6 +947,7 @@ def _get_litellm_prefix(self) -> Optional[str]:
         # Map provider class names to LiteLLM prefixes
         provider_prefixes = {
             "OpenAIProvider": None,  # Native format
+            "AtlasCloudProvider": "openai",  # Atlas Cloud uses OpenAI-compatible format
             "AnthropicProvider": None,  # Native format
             "GroqProvider": "groq",
             "TogetherProvider": "together_ai",
diff --git a/docs/INSTALLATION.md b/docs/INSTALLATION.md
index 6e44cdec..63a38d93 100644
--- a/docs/INSTALLATION.md
+++ b/docs/INSTALLATION.md
@@ -184,6 +184,7 @@ python examples/multi_provider.py
 | pydantic | Core validation | ✅ Always | requirements.txt |
 | httpx | Core HTTP client | ✅ Always | requirements.txt |
 | openai | OpenAIProvider | ❌ Optional | `[openai]` or `[providers]` or `[all]` |
+| atlascloud | AtlasCloudProvider | ❌ Optional | core package + `ATLASCLOUD_API_KEY` |
 | anthropic | AnthropicProvider | ❌ Optional | `[anthropic]` or `[providers]` or `[all]` |
 | groq | GroqProvider | ❌ Optional | `[groq]` or `[providers]` or `[all]` |
 | huggingface-hub | HuggingFaceProvider | ❌ Optional | `[huggingface]` or `[all]` |
diff --git a/tests/test_atlascloud.py b/tests/test_atlascloud.py
new file mode 100644
index 00000000..999fa5ca
--- /dev/null
+++ b/tests/test_atlascloud.py
@@ -0,0 +1,46 @@
+"""Tests for Atlas Cloud provider."""
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+from cascadeflow.providers import PROVIDER_REGISTRY
+from cascadeflow.providers.atlascloud import AtlasCloudProvider
+
+
+def test_init_with_api_key():
+    """Test initialization with explicit API key."""
+    provider = AtlasCloudProvider(api_key="atlas-test-key")
+
+    assert provider.api_key == "atlas-test-key"
+    assert provider.base_url == "https://api.atlascloud.ai/v1"
+    assert provider.name == "atlascloud"
+
+
+def test_init_from_env():
+    """Test initialization from ATLASCLOUD_API_KEY."""
+    with patch.dict(os.environ, {"ATLASCLOUD_API_KEY": "atlas-env-key"}, clear=True):
+        provider = AtlasCloudProvider()
+
+    assert provider.api_key == "atlas-env-key"
+    assert provider.base_url == "https://api.atlascloud.ai/v1"
+
+
+def test_init_no_api_key():
+    """Test initialization fails without Atlas Cloud API key."""
+    with patch.dict(os.environ, {}, clear=True):
+        with pytest.raises(ValueError, match="Atlas Cloud API key not found"):
+            AtlasCloudProvider()
+
+
+def test_custom_base_url():
+    """Test custom Atlas Cloud-compatible base URL."""
+    provider = AtlasCloudProvider(api_key="atlas-test-key", base_url="https://proxy.test/v1")
+
+    assert provider.base_url == "https://proxy.test/v1"
+
+
+def test_registered_provider():
+    """Test Atlas Cloud is registered for cascade agents."""
+    assert PROVIDER_REGISTRY["atlascloud"] is AtlasCloudProvider