[SITE-5247] Release note for final Gen 2 rollout of Solr 3 sites (#9825)

* Add release note for final Gen 2 rollout of Solr 3 sites

- New release note announcing Jan 7/14 rollout dates
- Update Gen 2 doc timeline table with Solr 3 sites
- Remove outdated Known Issues section

* Bump published date

---------

Co-authored-by: Rachel <[email protected]>

Author: pwtyler

src/source/content/php-runtime-generation-2.md

@@ -61,6 +61,8 @@ The table below contains the dates we upgraded sites to Gen 2 that were not set
 | October 29 | Performance/Elite | Dev/Multidevs |
 | November 3 | Basic | Test/Live |
 | November 17 | Performance/Elite | Test/Live |
+| January 7, 2026 | Solr 3 sites (all plans) | Dev/Multidev |
+| January 14, 2026 | Solr 3 sites (all plans) | Test/Live |
 
 
 <Alert type="info" title="Deploying code will upgrade test/live environments">
@@ -108,15 +110,11 @@ Once the Dev environment for a site has been upgraded to Generation 2, deploying
 
 <sup>1</sup> Review the <a href="/tls-compatibility">TLS documentation</a> to check which version of TLS your external connections are using, and how to ensure you are compatible with this change.<br /><br />
 
-## Known Issues
-
-- Drupal 8+ sites using Solr 3 are not compatible with PHP Runtime Generation 2.  [Upgrading to Solr 8](https://docs.pantheon.io/release-notes/2025/08/solr-3-drupal-94-eol) or disabling Solr is required. These sites were not included in the initial automatic upgrade rollout. The dev/multidev environments of these sites will be upgraded on December 9, and the test/live environments will be upgraded on December 16. Opting out of Generation 2 is still available for these sites.
-
 ## Reporting Issues
 
 If you encounter any issues with PHP Runtime Generation 2:
 
-1. Check the Known Issues section above
+1. Check the [Known Changes and Requirements](#known-changes-and-requirements) section above
 2. Verify the issue is related to the new PHP runtime by reverting back to `1` in your `pantheon.yml` file.
 3. Submit a detailed report through our [Support Portal](https://pantheon.io/support). Include "PHP Runtime Generation 2" in your message to support.
 

src/source/releasenotes/2026-01-08-final-generation-2-rollout.md

@@ -0,0 +1,24 @@
+---
+title: "Final PHP Runtime Generation 2 rollout for previously excluded Solr 3 sites"
+published_date: "2026-01-08"
+categories: [infrastructure]
+---
+
+The final set of sites previously excluded from the [PHP Runtime Generation 2](/php-runtime-generation-2) rollout are now being migrated. These sites were excluded because they were using Solr 3 with Drupal 9+. With [Solr 3 support for Drupal 9+ ending](/release-notes/2025/08/solr-3-drupal-94-eol) in December 2025, these sites are no longer excluded from the Generation 2 rollout.
+
+## Rollout Timeline
+
+| Start Date | Environments |
+|------------|--------------|
+| January 7, 2026 | Dev/Multidev |
+| January 14, 2026 | Test/Live |
+
+<Alert type="info" title="Deploying code will upgrade test/live environments">
+
+Once the Dev environment for a site has been upgraded to Generation 2, deploying commits from Dev to Test will automatically upgrade the Test environment to Generation 2 as well. Following this pattern, an upgrade to the Live environment takes place once commits are deployed from the Test to Live environment.
+
+</Alert>
+
+## Opting Out
+
+Sites may continue to [opt out of PHP Runtime Generation 2](/php-runtime-generation-2#q-how-do-i-opt-out-of-php-runtime-generation-2) until the [Gen 1 removal](/release-notes/2025/12/php-runtime-generation-1-removal-date) takes place starting April 6, 2026.