Sponsorship of the "we'll let you use some of our services for free" variety, rather than "we'll provide $$$" variety.

    ... open-source projects can enjoy a free Cloudflare Pro Plan, access
    to requested Cloudflare projects, and additional resources/support.

" Program criteria and eligibility

To qualify for our Open Source Sponsorship Program, projects must be open source and meet the following criteria:

Operate on a non-profit basis. Include a link back to our home page. "

So, funding in exchange for advertising? I accept that there's a cost for everything.

Tbf, putting a link to your sponsor costs you nothing and it's standard practice.

Doesn't seem to be any funding involved:

    ... open-source projects can enjoy a free Cloudflare Pro Plan, access
    to requested Cloudflare projects, and additional resources/support.

Direct link:

https://blog.cloudflare.com/cloudflare-new-oss-sponsorships-...