This is the list of the three editions of the game that appear on the store page, we'll go over its contents:

HITMAN World of Assassination Part One

This is the most INCOMPLETE EDITION, it contains:

• HITMAN 1 (2016) GOTY Edition

It's the worst version as it only has 1 game out of 3 and doesn't bring with it Freelancer mode or VR support.

Additional Note: Purchasing this HITMAN WoA Part One + Upgrade Pack will give you HITMAN World of Assassination Base Edition (detailed below).

HITMAN World of Assassination

This is the BASE EDITION of the game, it contains:

• HITMAN 1 with all its DLCs (GOTY Edition)
  
• HITMAN 2 (Standard Edition)
  
• HITMAN 3 (Standard Edition)

The only bad thing about this version is that it doesn't come with the content of HITMAN 2 Gold Edition so you'll have to buy the "HITMAN 3 Access Pass: HITMAN 2 Expansion" DLC.

https://store.steampowered.com/app/1829590/HITMAN_3_Access_Pass_HITMAN_2_Expansion/
This DLC is important as it will be necessary to experience the full story and have all the maps at your disposal (i.e. you will have HITMAN 2 Gold Edition If you buy this DLC alongside the base edition).

Additional note for completionists: Buying this Edition plus the DLC mentioned above are all you need to get 100% of the achievements.

HITMAN World of Assassination Deluxe Edition

This edition is obviously the most complete edition you can find. It contains:

• HITMAN 1 with all its DLCs (GOTY Edition)
  
• HITMAN 2 with all its DLCs (Gold Edition)
  
• HITMAN 3 with its DLCs for Seven Deadly Sins and Deluxe Pack (Deluxe Edition)

Upgrade HITMAN WoA Part One to HITMAN WoA

If you purchased HITMAN World of Assassination Part One, either by mistake or because you wanted to try the game, and now you want to upgrade to the base version, you can do so from here:

https://store.steampowered.com/sub/1230412/

Upgrade HITMAN WoA to HITMAN WoA Deluxe Edition

If you purchased the HITMAN World of Assassination version (or if you upgraded from Part One to WoA) and want to own the Deluxe Edition content, you must purchase this pack:

https://store.steampowered.com/bundle/30335/HITMAN_World_of_Assassination_Deluxe_Pack/

These DLCs have been added after the release of HITMAN 3 so, for whatever reasons, they have not been included in any edition of the game and must be purchased separately


https://store.steampowered.com/app/1829596/HITMAN_3__Trinity_Pack/?curator_clanid=41819667
This pack is purely cosmetic, it does not present any kind of in-game advantage. You can search for videos or images and, if you're interested, you can buy it whenever you want.

https://store.steampowered.com/app/2184790/HITMAN_3__Street_Art_Pack/?curator_clanid=41819667
This pack is purely cosmetic and are redesigns of existing weapons within the game.

https://store.steampowered.com/app/2184791/HITMAN_3__Makeshift_Pack/?curator_clanid=41819667
This pack is purely cosmetic and are redesigns of existing weapons within the game.

https://store.steampowered.com/app/2475260/HITMAN_3__Sarajevo_Six_Campaign_Pack/?curator_clanid=41819667
A DLC that was exclusive for a long time to the Playstation version; they are extremely easy missions (well, except for one) and don't reward you with anything when you complete them. I only recommend it if you don't think it's too much to pay for it.

https://store.steampowered.com/app/2828470/HITMAN_3__The_Undying_Pack/?curator_clanid=41819667
This DLC brings a Suit, tools (which are reskins of others already in the game) and an Arcade Mode mission that consists of 3 variants of the same Target.

https://store.steampowered.com/app/2973650/HITMAN_3__The_Disruptor_Pack/
This DLC brings a Suit, tools and an Arcade Mode mission that consists of 2 variants of the same Target.

https://store.steampowered.com/app/3110360/HITMAN_3__The_Drop_Pack/
This DLC brings a Suit, tools and an Arcade Mode mission that consists of 2 variants of the same Target.

https://store.steampowered.com/app/3254350/HITMAN_3__The_Splitter_Pack/
This DLC brings a Suit, tools and an Arcade Mode mission.

Here are some questions with their answers that can be useful to both newcomers and veterans of this franchise.

- HITMAN: Codename 47, HITMAN 2: Silent Assassin and HITMAN: Contracts are the HITMAN 1, 2 and 3 that HITMAN World of Assassination includes?
No, the last trilogy composed of HITMAN (2016), HITMAN 2 (2018), and HITMAN 3 (2021) are the games included in HITMAN WoA.
HITMAN: Codename 47 (2000), HITMAN 2: Silent Assassin (2002), and HITMAN: Contracts (2004) are different games.

- HITMAN WoA contains 3 games, does that mean that in my library I will have the 3 games separately?
No, all 3 games were integrated into one.

- I already have HITMAN (2016) and/or HITMAN 2 (2018) in my library, can I transfer all this content and buy only HITMAN 3 or the content I´m missing?
No, unfortunately you can't. Content transfer has been disabled in January 2023.

- I've played HITMAN and HITMAN 2 before but I don't want to repeat everything I did in those games, can I transfer my progress?
If you played HITMAN 2, you can transfer all that progress to HITMAN WoA. But, if you only played HITMAN (2016) you can't transfer that progress.

More information and progress transfer guide here:
https://ioisupport.zendesk.com/hc/en-us/articles/360019061577-Progression-Carryover-Guide?input_string=h3+from+epic+to+h3+steam

- How much space does HITMAN WoA take up on the disc?
Currently, the game size is 75.97 GB.

- I'm only interested in achievements and getting 100%, what do I need to buy?
You need the Base Edition of the game (HITMAN World of Assassination) + "HITMAN 3 Access Pass: HITMAN 2 Expansion" (Included in the Deluxe Edition).
https://store.steampowered.com/app/1829590/HITMAN_3_Access_Pass_HITMAN_2_Expansion/

I hope this guide has helped you clear up any doubts you have regarding what to buy about this great game!