Upwork currency is the US dollar: every rate, bid, contract and payment on Upwork is set and settled in USD, and freelancers convert to their local currency when they withdraw.
A profile in Lahore, Lagos or Lisbon shows its hourly rate in dollars, a job post's budget is in dollars, escrow holds dollars and the freelancer's balance is a dollar balance. Upwork pays out in US dollars; what happens next depends on the withdrawal method the freelancer chose. A direct transfer to a local bank account is converted by Upwork or its payment partner at a rate it sets, with any withdrawal fee taken on the way; a transfer to a dollar account or a payment service leaves the conversion to the freelancer, usually at a better rate and a different fee. Upwork publishes the current methods, fees and countries in its Help Center and changes them from time to time.
The practical effect is that currency risk sits with the freelancer and agency, not the client. A rate set in dollars buys a varying amount at home, and a freelancer in a country whose currency has fallen against the dollar earns more locally for the same work, which is one reason advertised rates by country move in ways that have nothing to do with skill. An agency's financial account is also held in dollars, and an agency that pays its members in local currency carries the conversion itself.
How Upwork Insights uses it
Every figure on this index is in US dollars as Upwork prints it: lifetime earnings, rates and medians, including the $30/hr median rate across the freelancer ranking and the country figures on the rate pages. Nothing is converted.