Today Thunderbird 153 is entering its alpha stage, also called Daily. We've started to adjust our roughly 250 patches to the new upstream code, with presently 35% done already. (Updates: 27th May 2026: 57% done, 31st May 2026: 87%).
We plan to release a Betterbird 153 beta, also called "future", when Thunderbird 153 beta is released on the 16th June 2026. Betterbird 153.0 ESR will ship around the 21st of July.
We'll see how immediately usable it will be. As a reminder, Thunderbird 102 and 128 initially shipped with backend dataloss issues, 115 had many frontend issues. These series stabilised at around dot release NNN.3.0. Let's hope that 153 will be equally quiet as 140. After all, Thunderbird has been shipping monthly releases from March 2025 (version 136), and despite those being regression-ridden, they have helped to improve the overall quality for the ESR release. Fingers crossed!