"Thus far" acts as an adverbial phrase, meaning it modifies a verb or adjective. It's usually used to indicate a point up to the present time.
Examples:
* Thus far, the project is on schedule. (The comma is used to set off the introductory phrase "Thus far.")
* We have been working hard thus far. (No comma is needed because "thus far" modifies the verb "have been working".)
* The team has been successful thus far. (No comma is needed because "thus far" modifies the adjective "successful.")
However, there might be some rare instances where you might use a comma, depending on the specific context and the flow of the sentence. For example:
* If "thus far" is used in a very long and complex sentence, a comma might be used to separate the phrase from the rest of the sentence for clarity.
In most cases, though, "thus far" does not need a comma before it.