CASRAI Dictionary

Tag: open access guidelines

  • 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?

    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.

    Feature PMC Open Access Subset Plan S US federal public access mandate
    Nature Repository licensing classification Funder policy mandate Federal agency policy (via OSTP)
    Governing body National Library of Medicine (NIH) cOAlition S funders Office of Science and Technology Policy (OSTP)
    What it governs Reuse rights of archived articles Where/how funded research is published Timing of public access to federally funded research
    Embargo position Not applicable — licence-based, not time-based Zero embargo required from 2021 Zero embargo required by 31 December 2025 (OSTP’s 2022 Nelson Memo)
    Geographic scope Global archive, US-hosted Primarily European and international funders United States federal agencies
    Enforcement mechanism None — it is a content filter, not a compliance check Funder grant conditions Agency public access plans

    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.

  • Plan S Green Open Access: Zero-Embargo Deposit Rules

    Plan S green open access is the compliance route that lets a researcher publish in the journal of their choice — including a subscription journal — and still meet their funder’s open access mandate, provided the Author’s Accepted Manuscript (AAM) or Version of Record (VoR) is deposited in a qualifying repository immediately on publication, with no embargo period and under a CC BY licence.

    Green open access is repository-based open access: the author (or their institution) self-archives a copy of the peer-reviewed article in an online repository, independently of whatever access model the publishing journal itself uses. Under cOAlition S’s implementation guidance, this route is one of three recognised paths to Plan S compliance, alongside publishing in a fully open access journal/platform and publishing under a transformative arrangement.

    What is green open access under Plan S?

    Green open access under Plan S is the “repository route” to compliance: a researcher publishes in a subscription journal and separately makes a copy freely available in an Open Access repository. It requires no article processing charge (APC), and does not depend on the publisher’s own access model — why research offices generally advise it as the lowest-cost compliance path.

    cOAlition S’s Principles and Implementation guidance states: “all scholarly articles that result from research funded by members of cOAlition S must be openly available immediately upon publication without any embargo period.” The green route is one of three ways to satisfy this.

    What are the zero-embargo deposit rules?

    The defining feature of Plan S green open access is that no embargo period is permitted — not the traditional 6- or 12-month delay still common elsewhere. Deposit and public availability must coincide with the publication date, including for early-view versions published online ahead of an issue.

    • Version deposited: either the Author’s Accepted Manuscript (the peer-reviewed, post-review text before publisher copy-editing and typesetting) or the Version of Record, at the publisher’s discretion.
    • Timing: immediate — deposit “no later than” publication date; retrospective or embargoed deposit does not satisfy Plan S.
    • Licence: the deposited copy must carry a Creative Commons Attribution (CC BY) 4.0 licence by default. cOAlition S accepts CC BY-SA 4.0 or CC0 as secondary alternatives, and will approve CC BY-ND only where a grantee explicitly requests and justifies it.
    • Rights basis: the author or their institution must retain sufficient rights — via copyright retention or a compliant licence to publish — to authorise the deposit themselves, rather than relying on publisher permission after the fact.

    This zero-embargo condition is what separates Plan S green OA from “traditional” green OA policies used by many institutional mandates (e.g. REF-linked UK policies), which commonly tolerate a delay before the AAM is made public.

    Which repositories qualify?

    Plan S does not publish a fixed whitelist of approved repositories. Instead, cOAlition S sets published technical criteria that any repository — institutional, subject-based, or general-purpose — must meet, and expects the repository to be listed in the Directory of Open Access Repositories (OpenDOAR) or in the process of registering.

    Under Part III of cOAlition S’s technical guidance, mandatory repository criteria include:

    • Persistent identifiers (PIDs) for deposited versions, such as a DOI.
    • High-quality, interoperable article-level metadata released under a CC0 public domain dedication, including complete funder and grant-number information.
    • Machine-readable open access status and licence information embedded in the article record.
    • Continuous availability, with uptime of at least 99.7% (excluding scheduled maintenance).
    • A functioning helpdesk — at minimum an email address — with a response time of no more than one business day.

    In practice, this means most well-run institutional repositories qualify, alongside subject repositories such as PubMed Central and Europe PMC for the life sciences, and general-purpose repositories such as Zenodo (which is itself referenced elsewhere in cOAlition S’s own guidance materials). Research offices should verify a specific repository’s registration status directly via OpenDOAR rather than assuming compliance from reputation alone.

    How does the green route differ from the Rights Retention Strategy?

    The green route and the Rights Retention Strategy (RRS) are related but distinct mechanisms, and conflating them is a common source of confusion in author-facing guidance. The green route is the compliance pathway — publish anywhere, deposit with zero embargo. RRS is the legal mechanism cOAlition S introduced to make that pathway enforceable even when a publisher’s standard licence-to-publish would otherwise block it.

    Under RRS, an author applies a CC BY licence to their AAM at the point of submission — before any publishing agreement is signed — via a standard rights-retention statement in the manuscript or cover letter. This pre-empts publisher terms that would otherwise impose an embargo, because the author’s declaration takes precedence. RRS is the tool that keeps zero-embargo green deposit available even in journals with no proactive compliant route.

    How does green compare with gold and hybrid (APC) routes?

    Gold open access means publishing directly in a fully open access journal or platform, where the article is freely available from the publisher at the point of publication — usually funded by an APC, which cOAlition S members will financially support. Hybrid — publishing open access within an otherwise subscription journal — is explicitly not supported by cOAlition S funding except within pre-approved transformative arrangements.

    Dimension Green (zero-embargo repository) Gold / OA journal Rights Retention Strategy
    Where you publish Any subscription journal Fully open access journal/platform Any journal (RRS is a licensing overlay, not a venue choice)
    Typical cost to author/funder No APC APC, funder-supported No APC
    Embargo permitted None None (immediate by definition) None
    Version deposited/published AAM or VoR, in a repository VoR, on publisher platform AAM, in a repository, licensed at submission
    Licence CC BY (default) CC BY (default) CC BY, asserted before any publisher agreement

    For research-office staff advising authors, the practical guidance is: green zero-embargo deposit is generally the cheapest compliant route, RRS is the safeguard that keeps it available when a publisher resists, and gold/APC remains appropriate where funder policy or discipline norms favour immediate publisher-side open access.

    Frequently asked questions

    What does green open access mean?

    Green open access means self-archiving a copy of a peer-reviewed article in an online repository — institutional, subject-based, or general-purpose — independently of the journal’s own access model. The author retains the ability to publish in any journal, including subscription titles, while separately making a version openly available at no cost to readers.

    What is the difference between gold and green open access?

    Gold open access means the publisher itself makes the article freely available immediately, typically funded by an APC. Green open access means the author self-archives a copy in a repository, which can apply even when the journal itself remains subscription-based, and normally carries no publication fee.

    Is green open access free?

    Yes. The green route generally involves no article processing charge to the author, funder, or institution. The only ongoing costs are the repository’s own infrastructure, which is typically funded institutionally rather than per-deposit, making green the lowest-cost Plan S compliance path for most authors.

    What is Plan S in open access?

    Plan S is an open access policy initiative launched by cOAlition S in September 2018, requiring that scholarly publications from research funded by its members be made immediately and openly available, with effect from 2021, via open access journals, platforms, or zero-embargo repository deposit.

    What this means for research offices

    Advising authors correctly requires distinguishing three separate questions: is the venue itself compliant (checked via cOAlition S’s Journal Checker Tool), does the author need Rights Retention to secure deposit rights, and is the target repository actually OpenDOAR-registered and criteria-compliant. Treating these as one question is the most common cause of authors believing they have complied when they have not — and it should be confirmed at submission, not after acceptance, since retrofitting a CC BY declaration onto a signed publisher agreement is frequently unenforceable.

    Outlook

    cOAlition S committed to a formal review of Plan S’s requirements, including the role of repository-based compliance, with several “strongly recommended” repository criteria (such as JATS XML full text and open citation data) flagged for possible upgrade to mandatory status. Research offices should expect repository technical requirements to tighten rather than relax, making early alignment with OpenDOAR criteria and RRS-based submission workflows a durable investment. For institutions building broader compliance workflows, see CASRAI’s research administration resources.