> For the complete documentation index, see [llms.txt](https://docs.thousandeyes.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.thousandeyes.com/product-documentation/browser-synthetics/dual-chromium-option/working-with-dual-chromium.md).

# Working with Dual Chromium

Use Dual Chromium to validate important page load tests and transaction tests against the newer Chromium track before that track becomes the default browser runtime.

Focus first on tests that monitor critical applications, use complex transaction scripts, or have failed during previous browser updates. Keep production monitoring on **Default** until you confirm the test behaves as expected on **Newer when available**.

### Validating a Test on the Newer Chromium Track

Use this workflow to compare a test on **Default** and **Newer when available**:

All Cloud Agents are enabled for Dual Chromium. To evaluate tests on Enterprise Agents, designate one Enterprise Agent as your canary agent and set **BrowserBot Package Type** to **Dual Chromium Version**.

For production tests, validate a duplicate test so the original test can stay on **Default**. For non-production tests, you can validate the existing test.

1. Identify a page load or transaction test that you want to validate.

   Start with business-critical tests, tests with complex scripts, or tests that depend on precise browser behavior.
2. If the test is used for production monitoring, duplicate the test.

   Use the duplicate for validation so the original test keeps its current agent assignments and Chromium setting.
3. Assign the validation test to one agent.

   To test with a Cloud Agent, keep any one Cloud Agent. To test with an Enterprise Agent, keep one Enterprise Agent that has **BrowserBot Package Type** set to **Dual Chromium Version**.
4. Open the test in **Network & App Synthetics > Test Settings**.
5. Set **Chromium Version** to **Newer when available**.

   For page load and transaction tests, this setting is under **Advanced Settings > Browser Options**.
6. Run an instant test, or let the scheduled test run on the selected agent.

   The instant test workflow replaces local validation of the newer Chromium version.
7. Compare the result with a recent run on **Default**.

   Review availability, errors, screenshots, waterfalls, timings, and transaction markers. In the test view, use the **Table** tab to confirm which Chromium version the run used.
8. If the test behaves as expected, keep **Chromium Version** set to **Newer when available** for continued validation.
9. If the test fails only on the newer track, set **Chromium Version** back to **Default** and troubleshoot the script before validating again.

### Investigating Failures After a Chromium Update

If a page load or transaction test starts failing after a Chromium update, check whether the failure appears only on the newer Chromium track.

1. Confirm that the test has **Chromium Version** set to **Newer when available**.
2. Confirm that the selected agent is a Cloud Agent, or that the selected Enterprise Agent has **BrowserBot Package Type** set to **Dual Chromium Version**.
3. In the test view, open the **Table** tab and confirm that the run used the newer Chromium version.
4. Compare the failed run with a recent successful run on **Default**.
5. Review the script, screenshots, waterfall, errors, and markers for browser behavior changes.

If the test works on **Default** but fails on **Newer when available**, keep the test on **Default** while you troubleshoot. If you need help, contact ThousandEyes Customer Support.

### Seeing the Chromium Version in Test Views

The page load and transaction test views show the Chromium version used for each Cloud Agent or Enterprise Agent in a test round. In **Network & App Synthetics > Views**, open the page load or transaction test view, then use the **Table** tab to check the Chromium version for each result.

For more information about test views, see [Views](https://docs.thousandeyes.com/product-documentation/internet-and-wan-monitoring/viewing-data).