To my knowledge the first beta version should be out in 2 a 3 weeks and after that alteast 2 a 3 months of testing before full release about suport for v4
committed to 12 months of bug fixes for Strapi v4 after v5 launches as well as an additional 6 months of security patches (meaning a total of 18 months of continued support for Strapi v4 after v5 launches).