The new HITMAN 3 listing on Steam includes a link to download a demo (thanks Frans). To be clear, this is the HITMAN 3 Starter Pack first released last April. As noted in this forum post on Steam, in addition to a sample of HITMAN 3, this allows users to import content and saved games from HITMAN 1 and 2. This post has the details from developer IO Interactive:

The HITMAN 3 Free Starter Pack will always give you FREE access to the ICA Facility, where you can experience the start of the World of Assassination trilogy, meet your handler and start earning XP and unlocks that will be carried over to the full game when you purchase it.

On top of permanent access to the ICA Facility, the HITMAN 3 Free Starter Pack will also periodically grant free access to other locations. For example, when the HITMAN 3 Free Starter Pack launches on 30 March, players will also experience the opening mission of HITMAN 2. The ‘Nightcall’ mission brings you to a moonlit beach and the roaring waves of Hawke’s Bay, New Zealand. Infiltrate a highly-secured luxury beach house in the dead of night and discover the secrets that lie within…