How does the IRS know about your selling of BTC?

Let’s say I wanted to sell $50k worth of BTC and cash out of Coinbase to pay off my mortgage. Let’s say I did it in increments of $9,000.

Does Coinbase give me a 1099 at the end of the year? Do they report that to IRS?

I’m wondering like how many people are actually reporting their gains on BTC. The thought of paying taxes on my BTC really pisses me off and yes I know all of the horror stories and not to mess with the IRS, but still. What are the chances of getting caught either underpaying or not paying taxes at all?