diff --git a/tests/nixos/s3-binary-cache-store.nix b/tests/nixos/s3-binary-cache-store.nix
index 0e01d0a01..154c1fb1b 100644
--- a/tests/nixos/s3-binary-cache-store.nix
+++ b/tests/nixos/s3-binary-cache-store.nix
@@ -789,6 +789,108 @@ in
 
           print("  ✓ Compressed log uploaded with multipart")
 
+      @setup_s3(
+          populate_bucket=[PKGS['A']],
+          profiles={
+              "valid": {"access_key": ACCESS_KEY, "secret_key": SECRET_KEY},
+              "invalid": {"access_key": "INVALIDKEY", "secret_key": "INVALIDSECRET"},
+          }
+      )
+      def test_profile_credentials(bucket):
+          """Test that profile-based credentials work without environment variables"""
+          print("\n=== Testing Profile-Based Credentials ===")
+
+          store_url = make_s3_url(bucket, profile="valid")
+
+          # Verify store info works with profile credentials (no env vars)
+          client.succeed(f"HOME=/root nix store info --store '{store_url}' >&2")
+          print("  ✓ nix store info works with profile credentials")
+
+          # Verify we can copy from the store using profile
+          verify_packages_in_store(client, PKGS['A'], should_exist=False)
+          client.succeed(f"HOME=/root nix copy --no-check-sigs --from '{store_url}' {PKGS['A']}")
+          verify_packages_in_store(client, PKGS['A'])
+          print("  ✓ nix copy works with profile credentials")
+
+          # Clean up the package we just copied so we can test invalid profile
+          client.succeed(f"nix store delete --ignore-liveness {PKGS['A']}")
+          verify_packages_in_store(client, PKGS['A'], should_exist=False)
+
+          # Verify invalid profile fails when trying to copy
+          invalid_url = make_s3_url(bucket, profile="invalid")
+          client.fail(f"HOME=/root nix copy --no-check-sigs --from '{invalid_url}' {PKGS['A']} 2>&1")
+          print("  ✓ Invalid profile credentials correctly rejected")
+
+      @setup_s3(
+          populate_bucket=[PKGS['A']],
+          profiles={
+              "wrong": {"access_key": "WRONGKEY", "secret_key": "WRONGSECRET"},
+          }
+      )
+      def test_env_vars_precedence(bucket):
+          """Test that environment variables take precedence over profile credentials"""
+          print("\n=== Testing Environment Variables Precedence ===")
+
+          # Use profile with wrong credentials, but provide correct creds via env vars
+          store_url = make_s3_url(bucket, profile="wrong")
+
+          # Ensure package is not in client store
+          verify_packages_in_store(client, PKGS['A'], should_exist=False)
+
+          # This should succeed because env vars (correct) override profile (wrong)
+          output = client.succeed(
+              f"HOME=/root {ENV_WITH_CREDS} nix copy --no-check-sigs --debug --from '{store_url}' {PKGS['A']} 2>&1"
+          )
+          print("  ✓ nix copy succeeded with env vars overriding wrong profile")
+
+          # Verify the credential chain shows Environment provider was added
+          if "Added AWS Environment Credential Provider" not in output:
+              print("Debug output:")
+              print(output)
+              raise Exception("Expected Environment provider to be added to chain")
+          print("  ✓ Environment provider added to credential chain")
+
+          # Clean up the package so we can test again without env vars
+          client.succeed(f"nix store delete --ignore-liveness {PKGS['A']}")
+          verify_packages_in_store(client, PKGS['A'], should_exist=False)
+
+          # Without env vars, same URL should fail (proving profile creds are actually wrong)
+          client.fail(f"HOME=/root nix copy --no-check-sigs --from '{store_url}' {PKGS['A']} 2>&1")
+          print("  ✓ Without env vars, wrong profile credentials correctly fail")
+
+      @setup_s3(
+          populate_bucket=[PKGS['A']],
+          profiles={
+              "testprofile": {"access_key": ACCESS_KEY, "secret_key": SECRET_KEY},
+          }
+      )
+      def test_credential_provider_chain(bucket):
+          """Test that debug logging shows which providers are added to the chain"""
+          print("\n=== Testing Credential Provider Chain Logging ===")
+
+          store_url = make_s3_url(bucket, profile="testprofile")
+
+          output = client.succeed(
+              f"HOME=/root nix store info --debug --store '{store_url}' 2>&1"
+          )
+
+          # For a named profile, we expect to see these providers in the chain
+          expected_providers = ["Environment", "Profile", "IMDS"]
+          for provider in expected_providers:
+              msg = f"Added AWS {provider} Credential Provider to chain for profile 'testprofile'"
+              if msg not in output:
+                  print("Debug output:")
+                  print(output)
+                  raise Exception(f"Expected to find: {msg}")
+              print(f"  ✓ {provider} provider added to chain")
+
+          # SSO should be skipped (no SSO config for this profile)
+          if "Skipped AWS SSO Credential Provider for profile 'testprofile'" not in output:
+              print("Debug output:")
+              print(output)
+              raise Exception("Expected SSO provider to be skipped")
+          print("  ✓ SSO provider correctly skipped (not configured)")
+
       # ============================================================================
       # Main Test Execution
       # ============================================================================
@@ -822,6 +924,9 @@ in
       test_multipart_upload_basic()
       test_multipart_threshold()
       test_multipart_with_log_compression()
+      test_profile_credentials()
+      test_env_vars_precedence()
+      test_credential_provider_chain()
 
       print("\n" + "="*80)
       print("✓ All S3 Binary Cache Store Tests Passed!")