What does "so far" mean?

Until now; up to this point in time.

Is "so far" formal or informal?

"so far" is register-neutral — appropriate in both casual and formal contexts. Used to describe what has happened or been done up to the current moment.

so far

入门 (A2) neutral

Until this moment.

"So far, everything is going smoothly."

在语境中听

The Nostalgia Critic and The Wall

Folding Ideas · 41:39

so far.

I Tried The World's Spiciest Snacks

Joshua Weissman · 8:24

so far.

50 Hours on Europe's Most Dangerous Island

Yes Theory · 12:37

So far.

I Hiked 72 Hours to Japan’s Most Isolated Mountain Village 🇯🇵 The Nakasendo

Abroad in Japan · 5:55

So far.

Data Structures: Crash Course Computer Science #14