Recently, when I was checking my Travis CI build statuses, I found out that they are transferring their services to
travis-ci.org. I looked more into it, and it turns out there is a plan to change the billing system.
For OSS repositories, you are given a 10K credit allotment which is around 1k Linux build minutes. Once that is up, they are hoping that you will consider on of their payed plans. But, for OSS projects, you can also submit a request to get more credits for your project.
They are doing this because they have seen increased abuse of the platform which increases the queue time for users that use it well.