Read Releases · platformio/platform-espressif32 · GitHub
The same is visible from the version number
since the format is <major packet version>.<underlying packet version>.<date>, so this means framework-espidf major packet version 3 (PIO-internal numbering), 40100 → 4.1.0 underlying version of ESP-IDF, date code 2020 27th August. Was also clarified in Find the mbed version which was used before a backup? - #3 by scottc11.