UPDATE

In April 2021, CryptoTaxAudit.com published the information requested by the IRS in crypto audits. Some spellings are different (e.g. "I.D." vs. "ID"), one typo was corrected ("in paper" -> "on paper"), but other imperfect wordings remained. The letter contains three additional items vs. the /r/bitcoin letter:

7. All records reconciling acquisition, whether by purchase or cryptocurrency-to-cryptocurrency (C2C) transaction, and sales, or other disposition such as C2C transaction histories or receipts and counterparties to all transactions
8. All records relating to investment expenses claimed with respect to any investments in virtual currency, including but not limited to invoices, receipts, canceled checks, bank records
9. All records relating to any lending or borrowing (on margin or otherwise) through fiat currency or in cryptocurrency

[List of all blockchain addresses owned or controlled by taxpayer]

I'm surprised this hasn't made it on the forum when it was posted on Reddit in Feb.

IRS Crypto tax AUDIT notice probes deep - original Reddit thread

Provide the following for all virtual currency transactions during the time period 01/01/2017-12/31/2017

• Detailed records for the acquisition and disposition of any virtual currency (domestic or international), including but not limited to:
  
  • Emails, screen prints, hardcopy prints, and transaction receipts maintained by the taxpayer or provided by any third-party such as an exchange, broker, or peer-to-peer facilitator (e.g. Paxful, Localbitcoins.com)
  • Wire transfer or direct deposit records, including automated clearing house (ACH) and electronic funds transfer (EFT) records.
  • List of all virtual currency kiosk (i.e., BTM or cryptocurrency kiosk or ATM) locations used along with copies of any transaction receipts or acknowledgements whether provided electronically or in paper.
  • A detailed list of cryptocurrency transactions involving cash including dates, input/output counterparties involved in the transaction, and the cryptocurrency involved
  • All correspondence (I.e., emails, texts, tweets, etc.) with all counterparties to any virtual currency transactions
  • List of all virtual currency received from hard forks, faucets, tipping, or any other method where a sale, buy, or exchange was not initiated by the receiver of cryptocurrency (commonly called airdrops), including date, type, and amount of virtual currency received with the date of sale, or other disposition, including amounts and description of what was received
  • Explanation of the method used to compute basis relating to the sale or other disposition of virtual currency
  • Records reflecting the valuation of any sale or other disposition of virtual currency at the time of acquisition and disposition
• Records relating to any expenses paid or items purchased (whether domestic or international) using virtual currency
• List of all blockchain addresses owned or controlled by taxpayer
• Records of all transactions relating to lending of virtual currency or use of virtual currency as collateral for loan, including, but not limited to, loan agreements, promissory notes, ledgers, transaction receipts, pledge, security, or collateralization agreements
• List of all digital currency exchanges (DCE) and peer-to-peer (P2P) facilitators (e.g., Coinbase, Paxful or Localbitcoins.com) (foreign and domestic) with associated user Ids, email addresses, IP addresses, and account numbers relating to those platforms
• List of all counterparties for any P2P virtual currency transactions (identifying the on-chain and off-chain transactions), email address, user IDs transactions.

This is not an all-inclusive list. Requests for additional information may be made if considered necessary.

Some people in that thread think the letter is fake because it uses two fonts and some other details. What do you guys think?

[for 2017]

I know Coinbase sent 1099-K forms for 2018, in early 2019 to eligible customers ("gross proceeds over $20,000 and more than 200 transactions").

But did they also send forms for 2017, when lots of people had gains? When did they start sending W-9 or 1099-K? I've seen a post from 2016 mentioning that.