Learn Icelandic: Gervigreindin mun gera hið óhugsandi. - Artificial intelligence will do the unthinkable.

When an adjective is used to represent a broad, abstract concept like 'the unthinkable' or 'the beautiful', Icelandic treats it as a noun. To do this, it uses the free-standing neuter definite article hið followed by the adjective.

Since hið usually triggers the weak declension, why doesn't óhugsandi change to end in an -a?

The word óhugsandi is a present participle. When present participles are used as adjectives, they are completely indeclinable. They keep the -andi ending no matter the gender, number, case, or strong/weak context.

Does hið óhugsandi mean a specific unthinkable thing, or unthinkable things in general?

It means the abstract concept of 'that which is unthinkable' as a whole. This substantivized neuter construction is perfect for sweeping abstract ideas, whereas if you meant specific unthinkable tasks, you would add a noun like óhugsandi hluti (unthinkable things).

Why does the sentence use mun gera instead of just the present tense gerir to show the future?

While the simple present tense frequently acts as the future in Icelandic, using the auxiliary verb munu (here as mun) adds a layer of prediction, deduction, or certainty. It sounds like a strong forecast about the inevitable path of technology.