This morning, we re-licensed Hack itself under the MIT license, and we will be doing the same for most of our Hack libraries and tools over the next few days, including the Hack Standard Library.

We’re relicensing Hack, these tools, and these libraries to a license that is broadly used in the community to ease concerns about compatibility, and to avoid holding back adoption for non-technical reasons.

HHVM itself remains under the PHP and Zend licenses.