How Does the Pool’s Software Communicate the Current Share Difficulty to the Mining Client?

The pool's software, specifically the Stratum server, communicates the current share difficulty to the mining client immediately upon connection and whenever the difficulty is adjusted (vardiff). This is done through a specific command within the Stratum protocol that includes the new difficulty target.

The mining client then uses this value to set the minimum requirement for a valid proof-of-work submission (a share).