diff --git a/src/anthropic/lib/credentials/_chain.py b/src/anthropic/lib/credentials/_chain.py
index 6e974a7b0..5be104ed1 100644
--- a/src/anthropic/lib/credentials/_chain.py
+++ b/src/anthropic/lib/credentials/_chain.py
@@ -32,7 +32,7 @@ def _build_federation_result(*, base_url: str) -> Optional[CredentialResult]:
     isn't fully set."""
     federation_rule_id = os.environ.get(ENV_FEDERATION_RULE_ID)
     organization_id = os.environ.get(ENV_ORGANIZATION_ID)
-    has_literal_token = ENV_IDENTITY_TOKEN in os.environ
+    has_literal_token = bool(os.environ.get(ENV_IDENTITY_TOKEN))
     identity_token_path = resolve_identity_token_path()
 
     if not federation_rule_id or not organization_id:
@@ -48,11 +48,11 @@ def _build_federation_result(*, base_url: str) -> Optional[CredentialResult]:
         # at the next token exchange (don't capture into a closure).
         def _read_env_token() -> str:
             value = os.environ.get(ENV_IDENTITY_TOKEN)
-            if value is None:
+            if not value:
                 raise CredentialsError(
-                    f"{ENV_IDENTITY_TOKEN} is not set; the workload-identity chain "
-                    f"selected this provider at construction time but the env var "
-                    f"is no longer present."
+                    f"{ENV_IDENTITY_TOKEN} is not set or is empty; the workload-identity chain "
+                    f"selected this provider at construction time but the env var no longer "
+                    f"contains an identity token."
                 )
             return value
 
diff --git a/tests/lib/test_empty_workload_identity_token.py b/tests/lib/test_empty_workload_identity_token.py
new file mode 100644
index 000000000..f9ecc82c0
--- /dev/null
+++ b/tests/lib/test_empty_workload_identity_token.py
@@ -0,0 +1,70 @@
+from __future__ import annotations
+
+import pathlib
+
+import pytest
+
+from anthropic import CredentialsError
+from anthropic.lib.credentials import _chain
+from anthropic.lib.credentials._constants import (
+    ENV_IDENTITY_TOKEN,
+    ENV_IDENTITY_TOKEN_FILE,
+    ENV_ORGANIZATION_ID,
+    ENV_FEDERATION_RULE_ID,
+)
+
+
+def test_empty_literal_identity_token_does_not_select_federation(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv(ENV_FEDERATION_RULE_ID, "fdrl_test")
+    monkeypatch.setenv(ENV_ORGANIZATION_ID, "org_test")
+    monkeypatch.setenv(ENV_IDENTITY_TOKEN, "")
+    monkeypatch.delenv(ENV_IDENTITY_TOKEN_FILE, raising=False)
+
+    assert _chain._build_federation_result(base_url="https://api.anthropic.com") is None
+
+
+def test_literal_identity_token_cleared_after_discovery_fails_before_exchange(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv(ENV_FEDERATION_RULE_ID, "fdrl_test")
+    monkeypatch.setenv(ENV_ORGANIZATION_ID, "org_test")
+    monkeypatch.setenv(ENV_IDENTITY_TOKEN, "initial-jwt")
+    monkeypatch.delenv(ENV_IDENTITY_TOKEN_FILE, raising=False)
+
+    result = _chain._build_federation_result(base_url="https://api.anthropic.com")
+    assert result is not None
+
+    monkeypatch.setenv(ENV_IDENTITY_TOKEN, "")
+    try:
+        with pytest.raises(CredentialsError, match="not set or is empty"):
+            result.provider()
+    finally:
+        close = getattr(result.provider, "close", None)
+        if close is not None:
+            close()
+
+
+def test_empty_literal_token_does_not_mask_identity_token_file(
+    monkeypatch: pytest.MonkeyPatch,
+    tmp_path: pathlib.Path,
+) -> None:
+    token_file = tmp_path / "identity-token"
+    token_file.write_text("file-jwt")
+
+    monkeypatch.setenv(ENV_FEDERATION_RULE_ID, "fdrl_test")
+    monkeypatch.setenv(ENV_ORGANIZATION_ID, "org_test")
+    monkeypatch.setenv(ENV_IDENTITY_TOKEN, "")
+    monkeypatch.setenv(ENV_IDENTITY_TOKEN_FILE, str(token_file))
+
+    result = _chain._build_federation_result(base_url="https://api.anthropic.com")
+    assert result is not None
+    try:
+        provider = result.provider
+        identity_provider = getattr(provider, "_identity_token_provider")
+        assert identity_provider() == "file-jwt"
+    finally:
+        close = getattr(result.provider, "close", None)
+        if close is not None:
+            close()