Subscribe to Open (S2O) is a no-fee open access model in which a publisher converts a subscription journal to open access for a given year only if enough existing library subscribers renew, replacing per-article processing charges (APCs) with pooled library budgets. Since cOAlition S formally endorsed S2O in April 2021 as a fee-free route to compliance, the model has become the de facto mechanism through which funders’ diamond open access ambitions meet publishers’ revenue realities — and research offices are now being asked to evaluate it as a recommendation, not just a curiosity.
Diamond open access is scholarly publishing in which neither authors nor readers pay to participate. Subscribe to open does not always meet the strict “community-owned” definition of diamond OA, but it eliminates author-facing fees and is increasingly treated by funders as an acceptable, scalable bridge toward that goal.
- What is Subscribe to Open and how does it work?
- How does S2O connect to cOAlition S’s diamond OA funding push?
- Which publishers have adopted Subscribe to Open?
- What should a research office evaluate before recommending S2O?
- Answer-first questions on Subscribe to Open
- What this means for institutional OA strategy
What is Subscribe to Open and how does it work?
Subscribe to Open was introduced in 2017 by Annual Reviews, developed with open access economist Raym Crow and backed by a grant from the Robert Wood Johnson Foundation. The mechanism is a mutual assurance contract: a publisher announces that if its existing library subscribers renew at the normal rate, that year’s content is made open to everyone; if participation falls short, the content stays behind the paywall for that year and the offer resets annually.
Unlike read-and-publish or transformative agreements, S2O requires no new invoicing infrastructure, no per-article accounting, and no author-facing fee at the point of submission. Libraries continue an existing subscription line item; the only change is what happens to the content if enough of them do so collectively.
- No APCs charged to authors, regardless of funder or institutional affiliation
- Existing library procurement and invoicing processes are reused unchanged
- Conversion is annual and reversible — an S2O journal can revert to subscription-only if a threshold is missed
- Some publishers sweeten renewal with discounted rates or backfile access to counter free-riding
How does S2O connect to cOAlition S’s diamond OA funding push?
cOAlition S — the group of research funders behind Plan S — formally endorsed Subscribe to Open on 27 April 2021, describing it as offering “a rapid route to open access that is applicable to research from all disciplines and all countries.” That endorsement matters because it gave grant-holders a funder-sanctioned way to satisfy immediate-OA mandates through journals that had not converted to APC-based gold OA.
The endorsement sits alongside cOAlition S’s broader diamond OA commitments. A 2021 study commissioned by cOAlition S and Science Europe — the OA Diamond Journals Study — identified roughly 29,000 diamond open access journals worldwide, publishing an estimated 356,000 articles a year without author or reader fees, a scale funders had previously underestimated. cOAlition S is also a signatory to the 2022 Action Plan for Diamond Open Access, which commits funders to building shared infrastructure for fee-free publishing rather than continuing to fund APCs indirectly through transformative agreements.
Read together, these three moves — the S2O endorsement, the diamond scale study, and the Action Plan — describe a funder preference: pay for access collectively through institutions, not per article through authors. Subscribe to open is the mechanism that lets existing subscription journals join that model without rebuilding their business from scratch.
Which publishers have adopted Subscribe to Open?
Adoption has moved from a single pilot to a recognisable segment of scholarly publishing. By 2023, roughly 15 publishers were running S2O across more than 150 journals, spanning learned societies, university presses, and disciplinary publishers.
| Publisher | S2O since | Scope | Notable outcome |
|---|---|---|---|
| Annual Reviews | 2017 | Originator; multiple review journals | Annual Review of Public Health usage rose eight-fold from May 2016 to May 2019; countries accessing it grew from 57 to 137 |
| IWA Publishing | 2021 | All 10 subscription journals | Met its revenue target while opening the full portfolio, after an earlier APC pilot proved financially unsustainable |
| Berghahn Books | 2020 | Anthropology journal portfolio (“Berghahn Open Anthro”) | Discipline-led equitable-access initiative built around subject-community buy-in rather than a single flagship title |
| Royal Society | 2025 | 8 subscription journals | Converts one of the largest remaining subscription portfolios in a single learned-society commitment |
Annual Reviews’ data point is the one funders cite most often: opening content did not just satisfy a mandate, it measurably expanded the readership base — evidence that S2O can deliver the access outcomes diamond OA is meant to produce, even where governance remains publisher-led rather than community-owned.
What should a research office evaluate before recommending S2O?
A research office weighing whether to recommend an S2O journal to a partner society, or to advise institutional libraries on participation, needs more than the funder endorsement. The following factors determine whether a given S2O offer is durable.
- Threshold transparency: does the publisher disclose the renewal percentage required, and report annually whether it was met?
- Free-rider exposure: what happens if institutions delay renewal expecting others to fund the opening — does the publisher offer renewal incentives to counter this?
- Reversibility risk: has the journal ever reverted to subscription-only after a missed threshold, and how was that communicated to authors mid-cycle?
- Governance fit: is the journal community-governed (closer to diamond OA) or publisher-owned with S2O as a funding mechanism only — a distinction that matters for funders assessing bibliodiversity commitments?
- Rights retention compatibility: does the journal’s S2O licence terms align with Plan S rights-retention requirements for the funder in question?
- Backfile and metrics access: what usage and participation data does the publisher share with subscribing libraries to justify continued renewal?
These questions should be answered before any recommendation is made to a partner journal or society considering conversion, since an S2O commitment carries annual renewal risk that a standard gold OA agreement does not.
Answer-first questions on Subscribe to Open
What does “Subscribe to Open” mean?
Subscribe to Open means a publisher converts a subscription journal to open access for a set period if enough existing library subscribers keep paying at the normal rate; no author fees are introduced, and the offer is renewed and re-evaluated every year based on subscriber participation.
What is Subscribe to Open (S2O)?
S2O is an economic model, first launched by Annual Reviews in 2017, that uses a mutual assurance contract: libraries are told their renewal will fund open access for everyone that year. It requires no new billing systems and has since been adopted by roughly 15 publishers across 150-plus journals.
What is an S2O subscription agreement?
An S2O agreement is a standard library subscription renewal with one added condition: if the publisher’s overall subscriber base renews at a sufficient rate, that year’s journal content becomes freely readable worldwide. If not, access reverts to subscribers only, with the offer repeated the following year.
Is Subscribe to Open the same as diamond open access?
Not exactly. Diamond open access requires community ownership and no fees for anyone; S2O guarantees no author fees but is typically publisher-led, funded by aggregated library subscriptions rather than a community-governed budget — which is why cOAlition S treats it as a compatible bridge rather than a diamond OA journal in the strict sense.
What this means for institutional OA strategy
For libraries and research offices, S2O shifts the evaluation question from “can our researchers afford the APC?” to “will enough of our peer institutions renew?” That is a collective-action problem, not a budgeting one, and it requires research offices to engage with consortial renewal conversations rather than individual author transactions.
For societies and mid-sized publishers weighing conversion, the Annual Reviews, IWA, Berghahn, and Royal Society cases show S2O working across very different scales and disciplines — from a single flagship title to an entire ten-journal portfolio. As cOAlition S’s funding priorities continue moving toward diamond-compatible, fee-free models over the 2026–2030 period, journals that can demonstrate stable S2O renewal rates are likely to find that status treated as evidence of funder-aligned sustainability, not merely an alternative to APCs.
Research administration teams evaluating open access routes for grant compliance should treat S2O as one option within a wider mandate landscape, alongside green open access and fully diamond-governed venues, rather than a universal substitute for either.