A Karaite website states
we only recognize the Miqra or Tanakh as divinely given.
They define tanach in the same way that we do.
{Basic Tenets of Karaism](http://www.karaiteinsights.com/article/what-is-karaism) states
- The Tanach (24 books of the Hebrew Bible) and only the Tanach have canonical status as the words of YHWH.
This article gives their view of "the chain of tradition from Moshe Rabbeinu at Sinai through Anshei Knesses Hegedolah and Shimon ben Shetach. They claim that their line of tradition continues through Shamai the Elder.
Karaite Judaism claims that Anan ben David was only organized the various groups into one unified group and lobbied the Caliphate (which ruled then) to accept them as a separate group with its own Raish Galusah (head of the exile). This article also claims that the original split was in the first century BCE (well after the Anshei Kneses Hagedolah).
Since Karaism was established after the Anshei Kneses Hagedolah "closed" Tana'ch (after Purim and before Chanukah) they accepted the definition already established. The articles shown below go into more detail.
The Karaites (according to Wikipedia can be dated back to the gaonic period. Some say that their roots go back to the Sadducees, though that is in dispute. In any case the split occurred after the second temple had been built and the definition of the tanach set by the Anshei Knesses Hagedolah.
Anan Ben David (c. 715
– 795 or 811?) (Hebrew: ענן בן דוד) is widely considered to be a
major founder of the Karaite movement.
According to Rabbi Avraham ben David, in his Sefer HaQabbalah, the
Karaite movement crystallized in Baghdad in the Gaonic period (circa
7th–9th centuries CE), under the Abbasid Caliphate in what is
present-day Iraq. This is the view universally accepted among Rabbinic
Jews. But, some Arab scholars (see cites) claim that Karaites were
already living in Egypt in the first half of the 7th century, based on
a legal document that the Karaite community in Egypt had in its
possession until the end of the 19th century, in which the first
Islamic governor ordered the leaders of the Rabbanite community
against interfering with Karaite practices or the way they celebrate
their holidays. It was said to have been stamped by the palm of 'Amr
ibn al-'As, the first Islamic governor of Egypt, and was reportedly
dated 20 AH (641 CE).
The Jewish Encyclopedia states that it was founded by Anan
The Karaites () = "Followers of the Bible") were a Jewish sect,
professing, in its religious observances and opinions, to follow the
Bible to the exclusion of rabbinical traditions and laws. But Karaism
in fact adopted a large part of rabbinical Judaism, either outright or
with more or less modification, while at the same time it borrowed
from earlier or later Jewish sects—Sadducees, Essenes, 'Isawites,
Yudghanites, etc.—as well as from the Mohammedans. The founder of the
sect being Anan, his followers were at first called Ananites, but as
the doctrines of the sect were more fully developed, and it gradually
emancipated itself from Ananism, they took the name of "Karaites," a
term first used by Benjamin al-Nahawendi ("Ba'ale Miḳra" at the end of
his "Sefer Linim") and in a quotation in "Yefet."
On Anan's death, between 780 and 800, his son Saul, and then his
grandson Josiah, succeeded him as head of the sect, but both of them
were too insignificant intellectually to leave many traces in Karaism.
But between 830 and 890 men of greater mark appeared among the
Karaites, who, while differing among themselves and creating various
subdivisions in the new sect, agreed in diverging from Anan's
doctrines, and even from his methods of teaching.
Thus, they had already accepted the canon from the Anshei Kneses Hagedola which ended after the establishment of Purim (Megilas Esther) and before the Chashmonaim (book of Maccabbes).
A Karaite website states
we only recognize the Miqra or Tanakh as divinely given.
They define tanach in the same way that we do.