PayJoin is a privacy improvement for bitcoin. Payjoin solves the sole privacy problem left open in the Bitcoin whitepaper, that transactions with multiple inputs "necessarily reveal that their inputs were owned by the same owner," because both the sender and receiver of a transfer contribute inputs to the transaction.
Transaction surveillance companies heavily depend on the common input ownership assumption which is broken by PayJoin transactions. So if those transactions became even a little bit widespread they could massively decrease the reliability of blockchain surveillance. Those who adopt PayJoin would find their privacy improved from strangers analyzing the blockchain. For example a surveillance company spy would find it much harder to figure out which addresses and transactions belonged to a particular merchant that was using PayJoin, or who else transacted to them.
PayJoin transactions can be made indistinguishable from regular bitcoin transactions by design, so it's very hard to get an accurate number for how common they are.
The most widely adopted PayJoin protocol standard is BIP 0078.
|Planned||The developers said they plan to|
|Non-BIP78||Implements a form of PayJoin but not BIP78|
|Extension||Can PayJoin using additional software|
|Yes||Feature has been released|
|Coldcard||Yes||Hardware can sign bip78 payjoins and also http://ckbunker.com/|
|Trezor Model One||Yes||https://stacker.news/items/174289|
|Trezor Model T||Yes||https://stacker.news/items/174289|
|BTCPay||Yes||First implementer of BIP78 payjoin for merchants.|
P2P exchanges make the most sense as early adoptors of PayJoin. All exchanges are welcome on this list of course.
|Name||Send to exchange||Receive from exchange||Notes|
|Sideshift.ai||Yes||No||For "To send" choose "Bitcoin PayJoin"|
|Human Rights Foundation||Yes||https://hrf.org/donate-bitcoin/payjoin/|
|Waxwing's personal donation page||Yes||https://joinmarket.me/donations/|
|Max Hillebrand's donation page||Yes||https://towardsliberty.com/btcpay/apps/27jLc1qpN8UXcQanHgeAsaEgLAio/pos|
Bitcoin casinos are very natural early-adopters of PayJoin. An early protocol specification for it, called bustapay, was created by the owner of a bitcoin casino.
|Aupa Beef Bars||Yes||https://twitter.com/EatAupa/status/1675307138288168960|
|Ideas Like Flames||Yes||https://twitter.com/ideaslikeflames/status/1389746824009949191|
|The Kratom Syndicate||Yes||https://thekratomsyndicate.com/blog/buying-kratom-with-payjoin.html|
|Namecheap||Yes||https://www.namecheap.com buy domains with BTCPayServer|
|Satoshi Coffee Co.||Yes||https://twitter.com/satscoffee/status/1679923696729837568|