Originally Posted by OpenSky

I was in Moscow the first day the sanctions stated. Seems like 4 years ago. The problems with Visa / Mastercard lasted probably a few days at most. That was at least 4 years ago.

The problem someone from the United States will encounter is the same problem you will find in Europe : the fact that most US cards are signature priority, and most do not support CHIP and PIN/ or offline PIN. Nobody in the world ( except in the US) swipes credit cards anymore, almost everyone authenticates a credit card transaction with a chip + 4 digit or more PIN. The US at least for uses Chip + Signature,. Since Russia does not get a lot of US visitors, most places outside Moscow will find it odd that you need to sign a credit card slip. Who does this? Nobody. Only people from the US.

As in Europe, you'll also find if difficult to buy train tickets from automated machines, unless you have a credit card from Barclays or a few others that support offline pin.

The international hotel chains are used to seeing American cards that need to be signed, the restaurants in Moscow will find it odd.

The other problem you will encounter is cards in Europe will text 4 digit authentication code to authenticate a transaction. Until recently it was near impossible to buy an S7 plane ticket on their website ( with a US card) because the website wanted that 4 digit code. Aeroflot 5 years ago had similar issues, all stemming for the fact that US credit cards are still stuck in the 1990s, in terms of security.

As far as I know everything works. Including JCB/Diners/Union pay, along with Visa/Mastercard/Amex of course.
Russia has an internal system called MIR which works in RU only

The hipsters in Moscow are fond of Apple Pay. PayPal also works, as does google pay.

You'll be fine.