Code is from a 2018 leak.
CSGO source code

Update (April 22, 2020 at 9:18PM ET): According to a statement issued to PC Gamer from Valve, the leaked code is only for CS:GO, but it does include "very old pieces of Team Fortress 2." Valve says that they will continue to investigate.

Valve also says that after an initial review of the leaked code they "believe it to be a reposting of a limited CS:GO engine code depot released to partners in late 2017, and originally leaked in 2018." The statement continues saying, "we have no found any reason for players to be alarmed or avoid the current builds."

Valve continues to say that should they find anything that is cause for alarm, they will notify news outlets and players. Until then, if you have any additional information about the leak, Valve would like to hear from you. Head on over to the Valve security page for more details.

Valve also posted a comforting update via their official Counter-Strike: Global Offensive Twitter.

Original story: For one reason or another, it looks like the source code for both Counter-Strike: Global Offensive and Team Fortress 2 has resurfaced after spending two years in hibernation. The Steam Database Twitter account notes that source code for both CS:GO and TF2 dated from between 2017 and 2018 is making the rounds again today. The thing is, this code seems to be the same code that was leaked back in late 2018. Naturally, a number of questions are being raised about this in the here and now.

First off, where did it come from? The code originally seems to have been "made available to Source engine licensees" back in late 2018. Now, whether or not that was an error on Valve's end that they quickly fixed, or if there was something more malicious at play, is not really known. If it is known, it's at least not known to me since I'm just going by what I can find right now about this. It was allegedly leaked, perhaps privately(?), back in late 2018 but had largely gone ignored.

According to the original source of the leak, which happens to be 4chan's /v/, the original poster says that the release purpose is to "further the interests of those that want to garner possible use out of these files, rather than them sitting on a dying harddrive." Again, we have no idea if the person on 4chan that posted this to the public is the source of the original leak or just someone who happened to grab it back in 2018 from another source. Today's leaker says that the last content included in the code for Counter-Strike is Operation Hydra, which released May 2017. The Team Fortress 2 code includes the Jungle Inferno content, which was made live in late October 2017.

As a little added twist to this story, it seems as though a lot of people are pointing fingers at ValveNewsNetwork's Tyler McVicker. Those anonymous users claim that McVicker is the source of the leak due. These claims seem to be based off of chat logs that may or may not be doctored. McVicker has issued a few statements proclaiming his innocence in this mess. His remarks on Twitter say that he is not the leaker, but does seem to have some evidence that he will be submitting to Valve. He also says that images of the chat logs that point to him being the leaker are doctored.

What does this all mean for players? Despite the code being over two years old, it can still lead to more cheats being developed and exploits being found. That is to say, it will be easier for cheat developers to develop said cheats. There is really no way to say just how damaging some of the exploits will be either. For now, assume the worst case scenarios.

Since this was originally leaked in 2018, it's possible that Valve completely rewrote both games or patched every potential exploitable hole. I wouldn't hold my breath on that having happened though as it would be a monumental undertaking.

Just as I was about to submit this news to the public, it looks as though some additional information has surfaced. Twitter user @JaycieErysdren, put up a 14-tweet chain that attempts to explain what the deal is with this leak and its ties to Tyler McVicker. I have included a copy and paste of the text below to make it a bit easier to read.

The explanation of every leak from today, April 22 2020. The reason that this leak happened is because one of Tyler's longtime associates was recently removed from Lever Softworks due to problematic behavior including racism, homophobia and transphobia.

This source was a regular of the the "Valve Cut Content" Discord community. This place is notoriously toxic, with this leaker being no exception. This person and I have never gotten along. This entire fiasco is simply retaliation for being removed from Lever Softworks just yesterday(!). Lever Softworks was formerly Tyler's game development group for Valve "beta" recreations, but in the last year or so has become more independent. The main project from Lever is a recreation of Valve's cancelled F-STOP concept. I've been an on-again-off-again member of Lever for the last 4 years or so, and I'm very familiar with this associate and their behavior. What follows will be an explanation of every individual item contained within this leak.

1. What are these source codes?
The source code present in the leak was given to many people in May 2018 by a mentally unstable source who wanted to cause damage to Valve. The CS:GO code is from May 2017, while the TF2 code is from November 2017. While Tyler never had direct access to the code, many of his associates had access and datamined it for the purpose of providing interesting information and trivia.

2. What are the chatlogs?
The chatlogs, with "Cephalon" and "YSU Calc II" are not related to the source code leak. In late 2016 Tyler was contacted by an unconfirmed source calling themself "Cephalon". The chatlog between Tyler and Cephalon was shared with several close friends, including the one who is responsible for this leak. The "YSU Calc II" Discord group was the place where all this information was shared and discussed for the better part of 2 years.

3. What is this "F-STOP" build?
The build of "F-STOP" is Lever Softworks' attempt at recreating Valve's cancelled project of the same name. It's very unfinished, with few maps and unfinished assets. None of it is in any way official or from Valve. Since the leaker was in the Lever Softworks group, and was removed just yesterday for the aforementioned problematic behavior, their username and work is all over the build.

4. "Valve VSS Images"?
This was something that I personally recieved[sic] from a Valve employee in 2018 while I was attempting to get the Gunman Chronicles source files. The images were sent to me so I could identify any folders that could be related to the game.

Unfortunately, nothing of the sort existed. These images were also shared with close friends, including Tyler and this leaker.

5. How does this effect[sic] Tyler?
It shouldn't do anything, really. Tyler is in contact with Valve and their legal team. They are aware of the situation and will be handling it WITH Tyler's assistance.

6. How will this effect Valve game communities?
There might be an increase in RCE*'s in TF2. Otherwise I'm not really an authority on it. It will almost certainly damage Valve's relationship with the Source Engine modding community. Beyond all of that, it's hard to say.
*Please note that in the above, I assume the use of RCE to mean "remote code execution." This is a security issue that allows attackers to access and potentially make unwanted changes to your computer. It has the potential of being very bad.

Make of this information what you will. It may yet be a while before we ever find out what is coming as a result of this leak. This applies to new cheats, new exploits made, legal repercussions, and potential changes to Valve's clamping down on sharing information and data that probably should not be shared outside of the company.

The image included in this post was the image posted by Steam Database on Twitter.