To the extent that with 以至 — Chinese grammar (HSK 6)

Cause，以至(于) + Resulting situation

以至 (yǐzhì), often expanded to 以至于, means "to the point that / so much so that" and introduces a result that goes surprisingly far. It usually starts the second clause, after a first clause describing an intense cause. English "so ... that ..." is the closest match.

Examples

他看书看得太专心，以至有人叫他都不知道。 Tā kàn shū kàn de tài zhuānxīn, yǐzhì yǒu rén jiào tā dōu bù zhīdào.	He was so absorbed in his book that he did not even notice someone calling him.
变化太大了，以至我几乎不认识这个城市了。 Biànhuà tài dà le, yǐzhì wǒ jīhū bù rènshi zhè ge chéngshì le.	The changes were so great that I could hardly recognise the city.
她太忙了，以至忘记了喝水。 Tā tài máng le, yǐzhì wàngjì le hē shuǐ.	She was so busy that she even forgot to drink water.

Tip: Do not confuse it with 以致, which introduces a bad result; 以至 simply marks degree.