At DrupalCon Vienna, we opened the opt-in period for module maintainers to volunteer their modules to be migrated to GitLab issues. You can opt yours in at #3409678: Opt-in GitLab issues.
That means that we will have some projects with issues on Drupal.org and some other projects with their issues on GitLab during this transition period. Due to this, some things will change in our current systems.
Changes to Drupal.org
The issue cockpit on each project's page will go away. The current issue cockpit that will see in projects reads data from our internal issues, but as projects transition to GitLab issues this block no longer makes sense. We will replace this for a simple "Issues" link that will take you to the right issue queue, whether it is GitLab or Drupal.org.

Parent and related issues will now be connected via a full URL. It used to be connected via entity reference fields, pointing at internal issues. Now that we have two systems for this, these will be links, that once rendered will bring the metadata information, like title and issue status, as we did with internal issues. We will be able to link both Drupal.org and GitLab issues into these new fields, and the old entity reference fields will go away.
What's next?
We ask project maintainers to help us at the Drupal Association iterate and improve on this process as we migrate more and more projects. We know that change can take time to be adopted, and we are really excited to help project maintainers move their issues into GitLab.
There are almost 200 projects with more than 1000 issues, and around 2000 projects with more than 100. 
Drupal "core" has more than 115K issues.
The roadmap will be (in each iteration, we will address feedback, fix bugs...):

Migrate projects that opted in
Make this the default for new projects
Migrate low-risk, low-usage, and/or sandbox projects
Migrate remaining projects, excluding a few selected high-volume, high-risk
Migrate the rest of the projects, including core

We are very excited about this transition, and we truly think it will be an improvement to the contribution experience. We are also thankful to the community for helping us with this.

The Drupal Association has received €201,000 from the Sovereign Tech Fund to enhance Drupal's GitLab infrastructure, with a focus on security, testing efficiency, and design tools. This funding will enable critical improvements including completing the migration of Drupal's security issue management system to GitLab, optimizing CI/CD testing across thousands of repositories, and implementing new tools for UX and design contributors.
This continues the Sovereign Tech Fund’s support of Drupal. In 2023, the Sovereign Tech Fund funded major work to support the move from Drupal.org's homebuilt contribution tools to the GitLab platform. 
The self-hosted GitLab instance at git.drupalcode.org is maintained by the Drupal Association and used by contributors all over the globe. In 2024, there were 7,276 unique individuals using git.drupalcode.org to contribute to 69,204 issues. These contributors represent an international community of users who support critical Drupal installations serving the public.
The additional funding will enable the Drupal Association to further enhance our use of GitLab in the following key areas:

Migrate security issue management to GitLab
Our existing security portal is running on an end-of-life version of Drupal, under extended support, and isn't integrated with our modern developer tools. Finalizing the move of our security team issue management to GitLab will provide the security team with better tools and make it easier to onboard new members.
 
Optimize CI/CD testing
We currently support testing for tens of thousands of repositories in the Drupal ecosystem. By further optimizing our testing configuration, we can reduce redundant tests, improve performance, and potentially expand to new types of testing like visual and performance regression testing.
 
Improve tools for UX and Design contributors
We'll implement better project management templates and explore integrating with design tools like Storybook and/or Figma to support our UX and Design contributors—who will then have the tools they need to help make Drupal easier, more intuitive, and more beautiful than ever. .
 
Share our CI strategy with other open source projects
We'll document and share our approach to managing CI testing across thousands of repositories to help other large open source projects facing similar challenges.
 

The work commissioned by the Sovereign Tech Fund will not only enable us to advance strategically, driving meaningful progress and making a positive impact within the Drupal community but also strengthen the open source platform for users everywhere.
We are grateful to the Sovereign Tech Fund for this collaboration. This funding reflects their continued dedication to open source and their confidence in the Drupal Association and the community's ability to innovate and ensure the future of web development.