$3k annually is correct. If one accumulates a large carryover loss, the entire balance can be used to offset gains in any calendar tax year. Losses are accounted for by long and short term, so it’s possible the term of the gain and offsetting loss would need to match.
correct to a point. Let's say you had 50,000 accumulative losses since 2015. But you happened to make 100,000 this year. You can write off all 50,000 to that 100,000 you made.