This new feature, currently in beta, will let you install games between PCs on the same network.

A new beta release for the Steam client rolled out this evening and with it came support for what Valve is calling "Local Network Game Transfers." To put it simply, this is a new feature that will let users copy existing Steam game installations and update files from one PC to another across their local area network (LAN).

Valve says that this feature will let you copy game files and updates to multiple PCs and even to your Steam Deck through your local area network. This will eliminate the need to download and install these games through the internet, which should help you reduce internet traffic. It may also speed up installs and updates on the additional devices.

A common use case would be a home setup with multiple PCs or Steam Decks on the same local network. Once a game is installed on one PC, all other PCs or the Steam Deck can install or update that game by transferring files directly from that one PC. A modern PC can easily transfer game content with 100MB/sec, and during the transfer the Steam client sending content will generate disk and CPU load (ie, you probably wouldn't want to be doing any intensive tasks on this PC during the transfer).
Valve also provided a couple of images showing what it looks like from the view of the host's machine (top) and what it looks like from the recipient's side (bottom).

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How it works is rather simple. Before you download a game or update on Steam it will first look to see if other PCs on your LAN already have the content. If one does, the client will "ask the Steam backend server to contact that other PC’s Steam client and start a game file transfer if local network transfers are enabled and possible." If the transfer is accepted, the client will try to download as much as it can from the host PC. If the connection is lost or there is no more content available, the client will fall back to using the public Steam content servers to get the rest.

In the beta client, there are currently four settings that will let you get things rolling (or not) with these Local Network Game Transfers.

There are four settings to specify what other PCs + Steam clients can be used for game file transfer. These settings are bi-directional, and to allow local transfers in, local transfers out are automatically enabled. The default setting is "Only my own devices", meaning you can only transfer in and out of PCs where your own account is logged into Steam.
  • Off - this client will not look for or allow local game file transfers. It will not download from or transfer to any other PC connected to your LAN.
  • Only my own devices - allow transfers to/from another device you are currently logged in with the same Steam account on your LAN (this is the default)
  • Only my friends - allow transfers to/from devices your Steam friends are logged into, connected to your LAN
  • Any user - allow transfers to/from any device that has Steam running and is connected to your LAN​
The requirements to use Local Network Game Transfers are some common sense things like making sure the devices are online and on the same LAN, or that settings on both the host and recipient device have this feature turned on, etc. One thing that sticks out here is the fact that only PCs running in Steam desktop mode can be the host. That means Steam Decks, PCs in Big Picture Mode, and custom launchers cannot transfer files out to other devices.

Valve also makes it clear that only game content is transferred in this system. You cannot transfer local save games or configuration files. You also cannot transfer Steam Workshop, Steam Cloud, or Steam Shader files. If you set your Steam client to allow for friends or any user to grab content from your machine on the LAN, they will be able to see what games you have installed. All transferred game content is compressed but not encrypted. Any data received from another Steam client is verified. Any invalid or corrupt data is ignored and will not be installed.