The American Physiological Society (APS) has adopted the Subscribe to Open (S2O) model for its 10 primary research journals.
Every year APS receives enough subscription support to transition to S2O, authors don’t pay any article processing charges (APCs) for accepted articles for that subscription year and those articles will be published open access.
If any of the APS journals do not meet a subscription threshold, they remain gated, with continued access for paying subscribers. Any articles published open access will be forever open and not gated.