diff --git a/tests/v1/kv_offload/tiering/test_obj_tier.py b/tests/v1/kv_offload/tiering/test_obj_tier.py
index 3df9d30691d..f429d6cf62d 100644
--- a/tests/v1/kv_offload/tiering/test_obj_tier.py
+++ b/tests/v1/kv_offload/tiering/test_obj_tier.py
@@ -25,6 +25,7 @@ from vllm.v1.kv_offload.base import (
     make_offload_key,
 )
 from vllm.v1.kv_offload.tiering.base import JobMetadata, JobResult
+from vllm.v1.kv_offload.tiering.obj.config import ObjStoreConfig
 from vllm.v1.kv_offload.tiering.obj.manager import ObjectStoreSecondaryTierManager
 
 # ---------------------------------------------------------------------------
@@ -418,3 +419,49 @@ class TestMockObjTierShutdown:
         tier, _ = _make_tier(num_blocks=4)
         tier.shutdown()
         tier.shutdown()  # must not raise
+
+
+class TestObjStoreConfig:
+    def test_explicit_credentials_included(self):
+        cfg = ObjStoreConfig(
+            bucket="b",
+            endpoint_override="ep",
+            access_key="ak",
+            secret_key="sk",
+        )
+        params = cfg.to_nixl_params()
+        assert params["access_key"] == "ak"
+        assert params["secret_key"] == "sk"
+
+    def test_credentials_omitted_when_empty(self):
+        cfg = ObjStoreConfig(bucket="b", endpoint_override="ep")
+        params = cfg.to_nixl_params()
+        assert "access_key" not in params
+        assert "secret_key" not in params
+        assert "session_token" not in params
+        assert "region" not in params
+        assert params["bucket"] == "b"
+        assert params["endpoint_override"] == "ep"
+
+    def test_session_token_and_region_included(self):
+        cfg = ObjStoreConfig(
+            bucket="b",
+            endpoint_override="ep",
+            access_key="ak",
+            secret_key="sk",
+            session_token="tok",
+            region="us-east-1",
+        )
+        params = cfg.to_nixl_params()
+        assert params["session_token"] == "tok"
+        assert params["region"] == "us-east-1"
+
+    def test_ca_bundle_included_when_set(self):
+        cfg = ObjStoreConfig(
+            bucket="b",
+            endpoint_override="ep",
+            ca_bundle="/path/to/ca.pem",
+        )
+        params = cfg.to_nixl_params()
+        assert params["ca_bundle"] == "/path/to/ca.pem"
+        assert "access_key" not in params
diff --git a/vllm/v1/kv_offload/tiering/obj/config.py b/vllm/v1/kv_offload/tiering/obj/config.py
index 5507c6a198e..76a1ae29e55 100644
--- a/vllm/v1/kv_offload/tiering/obj/config.py
+++ b/vllm/v1/kv_offload/tiering/obj/config.py
@@ -2,29 +2,45 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 """Connection configuration for the object store secondary tier."""
 
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 
 
 @dataclass
 class ObjStoreConfig:
-    """Connection parameters for an object store backend."""
+    """Connection parameters for an object store backend.
+
+    When ``access_key`` and ``secret_key`` are left empty the NIXL OBJ
+    plugin falls back to the AWS SDK default credential provider chain
+    (IAM roles, environment variables, credential files, etc.), which
+    enables workload-identity based auth on Kubernetes.
+    """
 
     bucket: str
     endpoint_override: str
-    access_key: str
-    secret_key: str
+    access_key: str = field(default="", repr=False)
+    secret_key: str = field(default="", repr=False)
+    session_token: str = field(default="", repr=False)
+    region: str = ""
     scheme: str = "http"
     ca_bundle: str = ""
 
     def to_nixl_params(self) -> dict[str, str]:
-        """Build the NIXL backend params dict."""
+        """Build the NIXL backend params dict.
+
+        Credential and optional fields are only included when non-empty
+        so that the AWS SDK default credential chain can activate.
+        """
         params: dict[str, str] = {
             "bucket": self.bucket,
             "endpoint_override": self.endpoint_override,
             "scheme": self.scheme,
-            "access_key": self.access_key,
-            "secret_key": self.secret_key,
         }
-        if self.ca_bundle:
-            params["ca_bundle"] = self.ca_bundle
+        # Omit empty optional fields so the NIXL OBJ plugin's underlying
+        # AWS SDK can fall back to its default credential provider chain
+        # (IAM roles, env vars, credential files, etc.).
+        # https://github.com/ai-dynamo/nixl/blob/main/src/plugins/obj/README.md
+        for key in ("access_key", "secret_key", "session_token", "region", "ca_bundle"):
+            value = getattr(self, key)
+            if value:
+                params[key] = value
         return params
diff --git a/vllm/v1/kv_offload/tiering/obj/manager.py b/vllm/v1/kv_offload/tiering/obj/manager.py
index 4c3fa754bf6..6060370ea06 100644
--- a/vllm/v1/kv_offload/tiering/obj/manager.py
+++ b/vllm/v1/kv_offload/tiering/obj/manager.py
@@ -157,8 +157,10 @@ class ObjectStoreSecondaryTierManager(SecondaryTierManager):
         except Exception as e:
             raise RuntimeError(
                 f"Object store tier connectivity probe failed — check bucket, "
-                f"endpoint_override, access_key, secret_key, and scheme. "
-                f"Error: {e}"
+                f"endpoint_override, and scheme. If using explicit credentials "
+                f"verify access_key and secret_key; otherwise ensure the AWS "
+                f"SDK default credential chain is configured (IAM role, env "
+                f"vars, credential file). Error: {e}"
             ) from e
 
     def _exists(self, obj_key: str) -> bool: