Rabbi Steinsaltz writes:
From the strictly historical point of view, the Talmud was never completed, never officially declared finished, without need for additional material.
The Bible, by comparison, underwent various stages of compilation and redaction, but was eventually completed, and it was categorically stated that no additions could be introduced.
The same was true of the Mishnah in its day.
But although a certain edition of the Talmud was regarded as definitive, this fact was not heralded by an official and public declaration that the work had reached its end and a new era had commenced.
The final edition of the Talmud may be compared to the stages of maturity of a living organism.
Like a tree, it has reached a certain form that is not likely to change substantially, although it continues to live, grow, and proliferate.
Although the organism has taken on this final form, it still produces new shoots that draw sustenance from the roots and continue to grow.
This fact is more important to our approach to the Talmud than it is to history.
The principle that the Talmud is unfinished holds out a constant challenge to continue the work of creation.
It is incumbent on every scholar to add to the Talmud and to contribute to the work, although it can never be finally completed.
–Rabbi Adin Steinsaltz