Unpaywall assigns an OA Status to every article, which you can find in the oa_status field of the API and dataset. There are five possible values: closed, green, gold, hybrid, and bronze. These terms are all commonly used in discussions of open access. Unfortunately, however, this is still not universal agreement on how to define them. Here are the definitions we use:

Green articles are published in toll-access journals, but archived in an OA archive, or "repository". These repositories may be discipline-specific (like ArXiv) or institutional repositories operated by universities or other institutions. Green articles may be published versions or preprints, and can have any license or no license.

Bronze articles are free to read on the publisher's website, without a license that grants any other rights. There may be a delay between publication and availability to read, and often articles can be removed unilaterally by the publisher.

Hybrid articles are free to read at the time of publication, with an open license. These are usually published in exchange for an article processing charge, or APC.

Gold articles have all the same characteristics as Hybrid articles, but are published in all-Open Access journals, which are in turn called "Gold journals", or just "OA journals".

When using these terms in the Unpaywall API, we've done our best to follow the most common usage. However, our definitions may not map well to your use case.  That's ok. All the properties we use to determine the oa_status are in the API and datasets. So you don't need to use our oa_status - you can make your own, using the same underlying data.

So, without further ado, here's a flowchart-style description of how we determine the oa_status for each article:

  • Ok, let's get started. Is the article open access?
    • no (is_oa = false): Ok, oa_status is  closed . Done.
    • yes (is_oa = true). Let's learn more. Where is the best copy of the article hosted?
      • In a repository (best_oa_location.host_type = "repository"): Ok, oa_status is  green . Done.
      • On the publisher website (best_oa_location.host_type = "publisher"). Let's learn more. Is the article published in a fully-OA journal?
        • yes (journal_is_oa = true): Ok, oa_status is  gold . Done.
        • no (journal_is_oa = false). Let's learn more. Is the article published under an open license?
          • yes (best_oa_location.license is not null): Ok, oa_status is  hybrid . Done.
          • no (best_oa_location.license is null): Ok, oa_status is  bronze . Done.

You can learn more about these terms and why we selected them in our paper, "The state of OA: a large-scale analysis of the prevalence and impact of Open Access articles," published in the journal PeerJ--particularly the literature review and methods sections.

In the browser extension, with OA Nerd Mode enabled, OA status is indicated by color:

hybrid or bronze

If a full text article is found by the extension - that is, not through our API - the tab color is always Bronze in OA Nerd Mode.