diff --git a/docs/04_automation_and_utility.md b/docs/04_automation_and_utility.md
index 636eb5f..05eaad4 100644
--- a/docs/04_automation_and_utility.md
+++ b/docs/04_automation_and_utility.md
@@ -1,5 +1,6 @@
 ---
 log:
+2026-11-07: Optimized `_get_adc_credentials` in `auth.py` to stub `google.auth._cloud_sdk.get_project_id` around `google.auth.default()`. When ADC user credentials lack a `quota_project_id`, `google-auth` otherwise spawns `gcloud config get-value project` on every CLI invocation to resolve a `project_id` that `_get_adc_credentials` immediately discards (`_`).
 2026-11-04: `colab drivemount` now opens the Drive consent URL in the system browser (`utils.open_url_in_browser`, also used by `colab pay`/`colab url --open`) instead of only printing it. The URL is still printed first, and a missing browser opener (SSH, containers, CI) is treated as normal: the flow keeps waiting for the user exactly as before. The prompt moved into `commands/automation.py::show_drive_auth_url` so it can be unit-tested.
 2026-11-02: Added `_check_linux_keyring_locked` in `auth.py` to inspect the active Linux `SecretService` collection via `secretstorage` before `get_password`/`set_password`, warning immediately when the keyring is locked so users know why the CLI is waiting on an unlock prompt (and suggesting `--auth=adc`).
 2026-10-29: Session history files are created readable only by the owner (0600), and existing ones are tightened to 0600 whenever the history logger starts.
diff --git a/src/colab_cli/auth.py b/src/colab_cli/auth.py
index 581aaf6..c67cd8f 100644
--- a/src/colab_cli/auth.py
+++ b/src/colab_cli/auth.py
@@ -299,7 +299,22 @@ def _get_adc_credentials() -> Credentials:
     # That warning shows up on every single `colab` invocation under ADC,
     # which is pure noise. Filter it, but keep the scope as tight as possible:
     # only this exact message, only during this one call.
-    with warnings.catch_warnings():
+    #
+    # Additionally, when ADC user credentials lack a `quota_project_id`,
+    # `google.auth._default._get_gcloud_sdk_credentials` calls
+    # `google.auth._cloud_sdk.get_project_id()`, which spawns a
+    # `gcloud config get-value project` subprocess (adding 2-13s of latency on
+    # every CLI invocation) solely to compute the second tuple element
+    # (`project_id`) that we immediately discard (`_`). Stubbing
+    # `get_project_id` during `google.auth.default()` avoids spawning `gcloud`
+    # while preserving the full ADC discovery chain.
+    from unittest.mock import patch as _patch
+    from google.auth import _cloud_sdk
+
+    with (
+        warnings.catch_warnings(),
+        _patch.object(_cloud_sdk, "get_project_id", return_value="colab-cli"),
+    ):
         warnings.filterwarnings(
             "ignore",
             message=r"Your application has authenticated using end user credentials.*",
diff --git a/tests/test_auth_adc.py b/tests/test_auth_adc.py
index 4e7ec5c..7f0cff7 100644
--- a/tests/test_auth_adc.py
+++ b/tests/test_auth_adc.py
@@ -200,3 +200,30 @@ def fake_default(*args, **kwargs):
     assert len(matching) == 1, (
         "Unrelated UserWarnings from google.auth must NOT be suppressed."
     )
+
+
+def test_get_credentials_adc_skips_gcloud_project_subprocess(mocker):
+    """When ADC user credentials have no quota_project_id, google.auth.default()
+    normally calls google.auth._cloud_sdk.get_project_id(), spawning a slow
+    `gcloud config get-value project` subprocess on every CLI invocation for a
+    project_id that _get_adc_credentials discards. Verify that subprocess path
+    is bypassed during google.auth.default()."""
+    from google.auth import _cloud_sdk
+
+    mock_creds = MagicMock()
+    mock_creds.requires_scopes = False
+
+    observed_project_id = []
+
+    def fake_default(*args, **kwargs):
+        observed_project_id.append(_cloud_sdk.get_project_id())
+        return mock_creds, observed_project_id[-1]
+
+    mocker.patch("google.auth.default", side_effect=fake_default)
+    m_subproc = mocker.patch("subprocess.check_output")
+    mocker.patch("colab_cli.auth.requests.AuthorizedSession")
+
+    get_credentials(provider=AuthProvider.ADC)
+
+    assert observed_project_id == ["colab-cli"]
+    m_subproc.assert_not_called()