PMC Open Access Subset vs Plan S: Not the Same

The PMC Open Access Subset and Plan S are not the same thing. The PMC Open Access Subset is a licensing classification inside PubMed Central (PMC) that flags which archived articles carry reuse-permitting licences for text mining and redistribution. Plan S is a funder mandate from cOAlition S that requires immediate open access publication of funded research. One is a repository filter; the other is a compliance requirement — and confusing them leads authors to think a PMC listing satisfies a funder’s open access policy when it may not.

The PMC Open Access Subset is the portion of PubMed Central’s full-text archive made available under Creative Commons or similar licences that permit reuse beyond reading, including text mining and redistribution. This distinction — repository versus mandate — is the source of a persistent mix-up among authors preparing to comply with funder open access requirements.

• What Is the PMC Open Access Subset?
• What Is Plan S?
• PMC Open Access Subset vs Plan S: Key Differences
• Does Plan S Compliance Require the PMC Open Access Subset?
• Common Questions
• Implications for Authors and Institutions

What Is the PMC Open Access Subset?

The PMC Open Access Subset is maintained by the U.S. National Library of Medicine (NLM), part of the National Institutes of Health (NIH). It contains articles and preprints made available under machine-readable licences — Creative Commons or similar — that permit reuse beyond simple reading access.

NLM groups the subset into three licence tiers:

• Commercial Use Allowed — CC0, CC BY, CC BY-SA, CC BY-ND licences
• Non-Commercial Use Only — CC BY-NC, CC BY-NC-SA, CC BY-NC-ND licences
• Other — no machine-readable licence, no licence, or a custom licence, with restricted redistribution on the PMC Cloud Service

As of the NIH’s most recent update, the subset spans well over 3.4 million journal articles and preprints, retrievable via the PMC FTP Service, Cloud Service, OAI-PMH Service, or BioC API. Not every article in PMC belongs to the Open Access Subset — many PMC-hosted articles remain under standard copyright and are excluded from bulk text-mining retrieval.

This is a critical, frequently missed distinction: PMC itself (the archive) and the NIH Public Access Policy (which mandates deposit of NIH-funded manuscripts into PMC) are separate from the Open Access Subset (the licensing classification). An article can be freely readable in PMC under the Public Access Policy while still sitting outside the Open Access Subset, because it lacks a reuse-permitting licence.

What Is Plan S?

Plan S is a funder-driven open access initiative launched in September 2018 by cOAlition S, a coalition of national and international research funders including UKRI, Wellcome, and members of the European Commission’s Horizon Europe programme. It requires that peer-reviewed publications arising from funded research be made immediately and fully open access, with no embargo period.

Under Plan S principles, compliant publication routes include:

• Publishing in a fully open access journal or platform
• Publishing in a subscription journal while depositing the accepted manuscript in an open access repository immediately on publication (the “Rights Retention Strategy”)
• Publishing on an open access platform or in a repository that meets cOAlition S technical requirements

cOAlition S states that authors or their institutions should retain copyright, and that a Creative Commons Attribution (CC BY) licence is the preferred licence type. Compliance is assessed against funder-specific policy terms, not against any single repository’s inclusion criteria.

PMC Open Access Subset vs Plan S: Key Differences

The clearest way to separate these two is by function: a repository classification versus a funder policy. The table below sets this alongside a third commonly conflated mechanism — the United States’ federal public access requirement — since UK and international researchers frequently encounter all three in the same compliance conversation.

The overlap that causes confusion: research funded under Plan S can end up in the PMC Open Access Subset if it carries a qualifying licence, but Plan S compliance is judged by the funder against its own policy terms, not by whether NLM has classified the article into the subset.

Does Plan S Compliance Require the PMC Open Access Subset?

No. Plan S does not name the PMC Open Access Subset as a compliance route. cOAlition S funders accept publication in a compliant journal, an institutional or subject repository meeting technical requirements, or immediate deposit of the accepted manuscript under an approved licence. PMC is one possible repository destination for biomedical research, but Plan S compliance is assessed by licence terms and embargo length, not by NLM’s internal subset classification.

Authors publishing biomedical research funded by a cOAlition S member should check the funder’s own open access policy and, separately, confirm whether their institution or publisher will additionally deposit the manuscript into PMC. These are two distinct actions that happen to intersect for US-relevant biomedical literature, not one unified process.

Common Questions

What is PMC open access?

PMC open access refers to the PMC Open Access Subset, the portion of PubMed Central archived under licences — typically Creative Commons — that permit reuse, including text mining and redistribution. It is not a funder policy; it is a licensing classification applied to specific articles already deposited in PMC.

Are PMC and PubMed the same?

No. PubMed is a database of citations and abstracts, while PMC (PubMed Central) is a full-text archive of biomedical journal articles. Both are maintained by the National Library of Medicine, but PubMed indexes metadata, whereas PMC stores the complete article text, of which only a subset carries reuse licences.

Is PMC free to use?

Yes, reading PMC articles is free. However, reuse rights differ by article: NLM states that PMC provides long-term preservation and free reading access, but text mining or redistribution beyond fair use requires the article to carry a qualifying licence within the Open Access Subset — free-to-read is not the same as free-to-reuse.

Implications for Authors and Institutions

For authors, the practical takeaway is definitive: satisfying a funder’s Plan S obligation and appearing in the PMC Open Access Subset are two separate compliance checks. Meeting one does not automatically satisfy the other. Institutional research administration teams tracking funder compliance should verify licence type, embargo length, and deposit location independently for each requirement, rather than treating “it’s in PMC” as proof of open access mandate compliance.

For publishers and repository managers, the distinction matters for metadata accuracy: an article’s PMC Open Access Subset licence tag should be checked and communicated separately from any funder compliance statement attached to the same article.

Looking ahead, the gap between these mechanisms is narrowing. The US federal government’s move toward zero-embargo public access by the end of 2025, alongside Plan S’s established zero-embargo requirement since 2021, signals convergence on immediate access as the global norm — even though the underlying legal and technical mechanisms (funder mandate versus repository licence versus agency policy) remain distinct and will continue to require separate verification.