The following schedule is subject to adjustment, but reflects the current thoughts on achievable milestones.

January 02-09, 2013 Confirm proposed scope and secure team leads.
January 09, 2013 Development begins.
April 04, 2013 Hard freeze on feature development. Stop feature development; focus on testing and compatibility (supported platforms, browsers, RTL, accessibilityAccessibility Accessibility (commonly shortened to a11y) refers to the design of products, devices, services, or environments for people with disabilities. The concept of accessible design ensures both “direct access” (i.e. unassisted) and “indirect access” meaning compatibility with a person’s assistive technology (for example, computer screen readers). (, etc). Ship a BetaBeta A pre-release of software that is given out to a large group of users to trial under real conditions. Beta versions have gone through alpha testing in-house and are generally fairly close in look, feel and function to the final product; however, design changes often occur as part of the process. 1.
From this point on, no more new feature requests in this release cycle, only fixes for issues in current features.
April 29, 2013 Beta 2
May 03, 2013 Beta 3
May 08, 2013 Release Candidaterelease candidate One of the final stages in the version release cycle, this version signals the potential to be a final release to the public. Also see alpha (beta). 1 target date. String freeze. Any work is focused on regressions and blockers only.
May 15, 2013 Release Candidate 2
May 20, 2013 Target date for WordPress 3.6 launch.

To get involved in WordPress coreCore Core is the set of software required to run WordPress. The Core Development Team builds WordPress. development, head on over to TracTrac An open source project by Edgewall Software that serves as a bug tracker and project management tool for WordPress. and pick a 3.6 ticket. Need help? Check out the Core Contributor Handbook.