This Upanishad was written by Sri Aurobindo during the early part of his stay in Pondicherry (1910-1914). It was first published in the journal Sri Aurobindo: Archives and Research in December 1978 with English translation done by Sri Jagannath Vedalankar.

There is Brahman alone, the One without a second. Being and non-being are its forms and It is also beyond Being and Non-Being. There is nothing else except That. All that is contained in the three times and all that is beyond the three times is indeed that One Brahman alone. Whatever is in the universe, small or large, noble or mean, is Brahman alone, Brahman alone. The world is also Brahman. It is true, not false.

That alone is the Transcendent Being, beyond all the three times, beyond all the worlds, penetrating all the worlds, beyond Being, beyond Non-Being, All-Being, All-Consciousness, All-Bliss, without beginning and end, the eternal Divine.

He is without quality and supports all qualities. He has qualities, infinite qualities, and enjoys the state of being without quality. He Himself transcends the state of being without qualities and the state of being with qualities. He is neither without quality nor with quality because He is One and Single.
The rooted and fundamental conception of Vedanta is that there exists somewhere, could we but find it, available to experience or self-revelation, if denied to intellectual research, a single truth comprehensive and universal in the light of which the whole of existence would stand revealed and explained both in its nature and its end. This universal existence, for all its multitude of objects and its diversity of faces, is one in substance and origin; and there is an unknown quantity, X or Brhaman to which it can be reduced, for from that it started and in and by that it still exists. This unknown quantity is called Brahman.
The Upanishads are Vedanta, a book of knowledge in a higher degree even than the Vedas, but knowledge in the profounder Indian sense of the word, jñāna. Not a mere thinking and considering by the intelligence, the pursuit and grasping of a mental form of truth by the intellectual mind, but a seeing of it with the soul and a total living in it with the power of the inner being, a spiritual seizing by a kind of identification with the object of knowledge is jñāna.