diff --git a/src/config/__init__.py b/src/config/__init__.py
index bd13e27..52f367c 100644
--- a/src/config/__init__.py
+++ b/src/config/__init__.py
@@ -145,8 +145,8 @@ class Settings(BaseSettings):
 
     # S3 Storage Configuration
     s3_endpoint: str = Field(default="localhost:3900")
-    s3_access_key: str = Field(default="test-access-key", min_length=3)
-    s3_secret_key: str = Field(default="test-secret-key", min_length=8)
+    s3_access_key: Optional[str] = Field(default=None)
+    s3_secret_key: Optional[str] = Field(default=None)
     s3_secure: bool = Field(default=False)
     s3_bucket: str = Field(default="code-interpreter-files")
     s3_region: str = Field(default="garage")
diff --git a/src/config/s3.py b/src/config/s3.py
index 0293279..c9e1d4a 100644
--- a/src/config/s3.py
+++ b/src/config/s3.py
@@ -1,19 +1,25 @@
 """S3-compatible object storage configuration."""
 
+from typing import Any, Optional
+
+import boto3
 from pydantic import Field
 from pydantic_settings import BaseSettings
 
 
 class S3Config(BaseSettings):
-    """S3-compatible storage settings (Garage, AWS S3, etc.)."""
+    """S3-compatible storage settings (Garage, AWS S3, etc.).
+
+    When ``access_key`` and ``secret_key`` are ``None`` (the default), boto3
+    uses its standard credential chain — environment variables,
+    ``~/.aws/credentials``, and EC2/ECS instance metadata (IAM role).  Set
+    them explicitly only when connecting to a non-AWS S3-compatible service
+    such as Garage or MinIO that requires static credentials.
+    """
 
     endpoint: str = Field(default="localhost:3900", alias="s3_endpoint")
-    access_key: str = Field(
-        default="test-access-key", min_length=3, alias="s3_access_key"
-    )
-    secret_key: str = Field(
-        default="test-secret-key", min_length=8, alias="s3_secret_key"
-    )
+    access_key: Optional[str] = Field(default=None, alias="s3_access_key")
+    secret_key: Optional[str] = Field(default=None, alias="s3_secret_key")
     secure: bool = Field(default=False, alias="s3_secure")
     bucket: str = Field(default="code-interpreter-files", alias="s3_bucket")
     region: str = Field(default="garage", alias="s3_region")
@@ -24,6 +30,31 @@ def endpoint_url(self) -> str:
         scheme = "https" if self.secure else "http"
         return f"{scheme}://{self.endpoint}"
 
+    def make_client(self) -> Any:
+        """Return a configured boto3 S3 client.
+
+        Credentials are passed explicitly only when both ``access_key`` and
+        ``secret_key`` are set. When they are ``None``, boto3 falls through to
+        its default credential chain (env vars, ``~/.aws/credentials``, EC2/ECS
+        instance metadata).
+
+        Raises ``ValueError`` when exactly one of the pair is set — partial
+        static config is always a misconfiguration.
+        """
+        if bool(self.access_key) != bool(self.secret_key):
+            raise ValueError(
+                "S3_ACCESS_KEY and S3_SECRET_KEY must both be set or both be unset. "
+                "Partial static credentials are not supported."
+            )
+        kwargs: dict[str, Any] = {
+            "endpoint_url": self.endpoint_url,
+            "region_name": self.region,
+        }
+        if self.access_key and self.secret_key:
+            kwargs["aws_access_key_id"] = self.access_key
+            kwargs["aws_secret_access_key"] = self.secret_key
+        return boto3.client("s3", **kwargs)
+
     class Config:
         env_prefix = ""
         extra = "ignore"
diff --git a/src/services/file.py b/src/services/file.py
index 5d12c01..939bd9d 100644
--- a/src/services/file.py
+++ b/src/services/file.py
@@ -6,7 +6,6 @@
 from typing import List, Optional, Tuple, Dict, Any
 
 # Third-party imports
-import boto3
 import redis.asyncio as redis
 import structlog
 from botocore.exceptions import ClientError
@@ -25,13 +24,7 @@ class FileService(FileServiceInterface):
 
     def __init__(self):
         """Initialize the file service with S3 and Redis clients."""
-        self.s3_client = boto3.client(
-            "s3",
-            endpoint_url=settings.s3.endpoint_url,
-            aws_access_key_id=settings.s3_access_key,
-            aws_secret_access_key=settings.s3_secret_key,
-            region_name=settings.s3_region,
-        )
+        self.s3_client = settings.s3.make_client()
 
         # Initialize Redis client
         self.redis_client = redis.from_url(
diff --git a/src/services/health.py b/src/services/health.py
index 0027c51..e86f5c4 100644
--- a/src/services/health.py
+++ b/src/services/health.py
@@ -11,7 +11,6 @@
 from typing import Dict, Any, Optional
 
 # Third-party imports
-import boto3
 import redis.asyncio as redis
 import structlog
 from botocore.exceptions import ClientError
@@ -224,21 +223,11 @@ async def check_s3(self) -> HealthCheckResult:
 
         try:
             if not self._s3_client:
-                self._s3_client = boto3.client(
-                    "s3",
-                    endpoint_url=settings.s3.endpoint_url,
-                    aws_access_key_id=settings.s3_access_key,
-                    aws_secret_access_key=settings.s3_secret_key,
-                    region_name=settings.s3_region,
-                )
+                self._s3_client = settings.s3.make_client()
 
             loop = asyncio.get_event_loop()
-            buckets_resp = await loop.run_in_executor(
-                None, self._s3_client.list_buckets
-            )
-            buckets = buckets_resp.get("Buckets", [])
 
-            # Check if our bucket exists
+            # Check if our bucket exists; create it if not
             try:
                 await loop.run_in_executor(
                     None,
@@ -300,7 +289,6 @@ async def check_s3(self) -> HealthCheckResult:
                 "endpoint": settings.s3_endpoint,
                 "bucket": settings.s3_bucket,
                 "bucket_exists": bucket_exists,
-                "total_buckets": len(buckets),
                 "secure": settings.s3_secure,
             }
 
diff --git a/src/services/state_archival.py b/src/services/state_archival.py
index 2d05d12..915a9d1 100644
--- a/src/services/state_archival.py
+++ b/src/services/state_archival.py
@@ -22,7 +22,6 @@
 from datetime import datetime, timezone
 from typing import Optional, Dict, Any
 
-import boto3
 import structlog
 from botocore.exceptions import ClientError
 
@@ -58,13 +57,7 @@ def __init__(
             s3_client: Optional boto3 S3 client (creates new one if not provided)
         """
         self.state_service = state_service or StateService()
-        self.s3_client = s3_client or boto3.client(
-            "s3",
-            endpoint_url=settings.s3.endpoint_url,
-            aws_access_key_id=settings.s3_access_key,
-            aws_secret_access_key=settings.s3_secret_key,
-            region_name=settings.s3_region,
-        )
+        self.s3_client = s3_client or settings.s3.make_client()
         self.bucket_name = settings.s3_bucket
         self._bucket_checked = False
 
diff --git a/src/utils/config_validator.py b/src/utils/config_validator.py
index 237ed6a..36b8ae5 100644
--- a/src/utils/config_validator.py
+++ b/src/utils/config_validator.py
@@ -4,7 +4,6 @@
 import shutil
 from typing import List, Dict, Any
 import redis
-import boto3
 from botocore.exceptions import ClientError
 
 from ..config import settings
@@ -124,26 +123,18 @@ def _validate_redis_connection(self):
     def _validate_s3_connection(self):
         """Validate S3 storage connection."""
         try:
-            client = boto3.client(
-                "s3",
-                endpoint_url=settings.s3.endpoint_url,
-                aws_access_key_id=settings.s3_access_key,
-                aws_secret_access_key=settings.s3_secret_key,
-                region_name=settings.s3_region,
-            )
-
-            # Test connection by listing buckets
-            response = client.list_buckets()
-            buckets = response.get("Buckets", [])
-
-            # Check if our bucket exists
-            bucket_exists = any(
-                bucket["Name"] == settings.s3_bucket for bucket in buckets
-            )
-            if not bucket_exists:
-                self.warnings.append(
-                    f"S3 bucket '{settings.s3_bucket}' does not exist - will be created"
-                )
+            client = settings.s3.make_client()
+
+            try:
+                client.head_bucket(Bucket=settings.s3_bucket)
+            except ClientError as e:
+                code = e.response["Error"]["Code"]
+                if code in ("404", "NoSuchBucket"):
+                    self.warnings.append(
+                        f"S3 bucket '{settings.s3_bucket}' does not exist"
+                    )
+                else:
+                    raise
 
         except ClientError as e:
             if settings.api_debug:
diff --git a/tests/conftest.py b/tests/conftest.py
index 37e432c..bad9dd1 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -115,10 +115,9 @@ def execution_service(mock_sandbox_manager):
 @pytest.fixture
 def file_service(mock_s3_client, mock_redis):
     """Create FileService instance with mocked dependencies."""
-    with patch("src.services.file.boto3") as mock_boto3, patch(
+    with patch("src.config.s3.S3Config.make_client", return_value=mock_s3_client), patch(
         "src.services.file.redis.from_url", return_value=mock_redis
     ):
-        mock_boto3.client.return_value = mock_s3_client
         service = FileService()
         yield service
 
diff --git a/tests/unit/test_file_service.py b/tests/unit/test_file_service.py
index 58aebb6..f838171 100644
--- a/tests/unit/test_file_service.py
+++ b/tests/unit/test_file_service.py
@@ -39,8 +39,7 @@ def mock_redis_client():
 @pytest.fixture
 def file_service(mock_s3_client, mock_redis_client):
     """Create FileService with mocked clients."""
-    with patch("src.services.file.boto3") as mock_boto3:
-        mock_boto3.client.return_value = mock_s3_client
+    with patch("src.config.s3.S3Config.make_client", return_value=mock_s3_client):
         with patch("src.services.file.redis.from_url") as mock_redis_from_url:
             mock_redis_from_url.return_value = mock_redis_client
             service = FileService()