The Subscribe-to-Open (S2O) model is an open science model that relies on sufficient support from the mathematical community in favor of the publisher to ensure free access to the relevant content, all without publication fees for the authors. This support is measured in the number of paid subscriptions contracted for a given year (and for a given journal).
Here is the precise description of the S2O model. Paid subscriptions for the reference year are tallied, and when this number exceeds a certain threshold (corresponding to a break-even point for the journal), all articles published in that journal become freely accessible on the SMF website. Until the threshold is reached, articles are only accessible to institutions and individuals who have already subscribed. The opening of the journal can thus occur at any time during the year or may not occur in a given year if community support is insufficient.
This mechanism is reset on January 1st of each year: a journal can, therefore, be freely accessible in a given year regardless of the situation in previous years.
This model, of course, allows users the option to refrain from subscribing to take advantage of a potential opening of the journal. We emphasize that, conversely, S2O should be perceived as an opportunity for historical subscribers to become contributors to the openness of science, and we are confident that the vast majority of subscriptions will be renewed for 2023, a condition that alone will enable the opening of the Bulletin de la Société Mathématique de France.