Reason

#2 sounds a bit clumsy to me.
Are you asking if it has the same meaning as #1?

CliveAre you asking if it has the same meaning as #1?

In this case, not really.

I'm just wondering if "The reason is+to-infinitive" works as fine as "The reason is+that/because-clause."

Both sentences are okay from a purely technical-grammatical point of view. However, the problem with both is that you would rarely, if ever, use either in real life speech. In what context could these be used? I cannot, offhand, think of any situation where either would fit. In real life speech you would say, rather, something like:

I have to go.

Just go.

Go.