I had something like 50k+ transactions last year. Cointracking wouldn’t create a 8949 for me because their servers couldn’t handle a dataset that large, but they could create a capital gains CSV file that was super easy for my acccountant to sum up a few columns and make the 8949. That said, their very high transaction count plans are $1000+, which seems insane. Through a bug they had interfacing with HitBtc I was able to get the CSV for free, but next year I doubt I’ll use this service at that high price.