Pokémon Go players can trade with people up to 12 kilometers — about 7.4 miles — away through Nov. 16.

Pokémon Go is allowing players to trade Pokémon from a further distance, from Nov. 12 until Nov. 16.
Though Niantics English post about the update did not state how far the distance allowed is, a Korean announcement confirmed that the maximum range you can trade is 12 kilometers (approximately 7.4 miles). Normally, you can only trade with a person if youre standing close to them. This means you will not be able to give all your coworkers who live several states away the Pansage that you caught for them on your trip to Asia in January, but you will be able to trade with your buddy who lives in your area. Ahem.
The distance limits on trading has been a frequently complained about issue among players, though its notably in place to prevent the selling of rare Pokémon. If you can trade from a far distance, itd be easier for people to complete real money transactions for Shiny, Legendary, or regional Pokémon. Some fans have suggested that only best friends or lucky friends in-game should be able to remote trade to solve this problem, but Niantic has never implemented this.