As noted above, 'Fully Open Access' does not mean completely free. So, while this change is welcome, there are still a lot of pricing/licensing options:
Also, the 'Basic Edition' provided for free to individuals without institutional/individual accounts, the ACM explains, does not include niceties such as 'Advanced Search' (e.g., filters), which requires an upgrade https://live.staticflickr.com/65535/55017806873_c9ba2490c1_b...