Valve’s latest SteamOS 3.7.20 beta quietly adds the ntsync driver, a kernel change that can smooth out older Windows shooters like classic Call of Duty on Steam Deck. Here’s what changed, what early tests show, and whether multiplayer nostalgists should opt into the beta.
SteamOS 3.7.20 just hit the Beta and Preview channels for Steam Deck, and on paper it looks like a tiny patch: the headline change is a single line in the notes, “Added ntsync driver.” For older Windows shooters, especially classic Call of Duty on Steam Deck, that one line matters a lot more than it looks.
If your Deck time is mostly spent in late‑2000s and early‑2010s multiplayer lobbies, this is the first system update in a while that is really worth paying attention to.
What Valve actually changed in SteamOS 3.7.20
The official SteamOS 3.7.20 Beta: Last Call notes from Valve list only a couple of tweaks for Deck owners. The big one is that the Linux kernel on SteamOS now includes and auto‑loads the ntsync driver by default.
Ntsync is a kernel‑level implementation of Windows NT synchronization primitives. In plain terms, it lets Proton and Wine talk to the Linux kernel using constructs that behave much more like what Windows games expect when they create and wait on things like events, semaphores and mutexes.
Until now, SteamOS has leaned on fsync (and before that futex2) to accelerate this kind of synchronization. Fsync already provides high performance for many games and is one of the reasons modern AAA titles run as well as they do on Deck. But it is still a translation layer, not a one‑to‑one match for how older Windows games drive their threads.
By enabling ntsync in the kernel, Valve is essentially laying down a more native‑feeling path for Proton builds that know how to use it. Right now that mostly means Proton‑GE, since it added ntsync support ahead of Valve’s own Proton releases. SteamOS 3.7.20 does not magically flip every game over to ntsync, but it removes the system‑level blocker so compatible Proton builds can take advantage.
Beyond ntsync, the update also touches InputPlumber security under the hood for non‑Deck devices, but that has no real impact on game performance. For Deck owners worried about regressions, 3.7.20 is a very focused technical change rather than a sweeping UI or feature overhaul.
Why older Call of Duty titles care about ntsync
Classic Windows shooters were built against a very specific expectation of how Windows handles threads and synchronization. A lot of that code dates back to an era where single‑ or dual‑core CPUs were common and developers carefully tuned how work hopped between threads to keep mouse input and rendering smooth.
On Proton with only fsync available, some of those assumptions do not hold perfectly. You can see it in games that technically hit high frame rates but still feel uneven, hitch during explosions or suddenly tank their frame time when lots of AI or physics kicks off.
Ntsync tackles that by more faithfully mirroring the Windows synchronization model at the kernel level. In practice, that can mean fewer stalls when the game threads are waking each other up, less CPU time wasted in translation overhead, and smoother pacing when a title aggressively spawns or waits on synchronization objects.
This is especially interesting for older Call of Duty games that have historically been awkward on Deck, even when their raw GPU demands are trivial for the hardware.
Early performance impressions on Steam Deck
Because 3.7.20 is still in beta, the data set is small and mostly comes from community tests and a handful of press benchmarks, but there are already a few clear themes.
Call of Duty 4: Modern Warfare
PCGamesN tested the Call of Duty 4: Modern Warfare campaign on a Steam Deck OLED. Using a checkpoint in the second mission as a repeatable scene, they compared a standard fsync‑only setup to a Proton‑GE build that can use ntsync under the new SteamOS kernel.
With the standard fsync path, frame rates hovered around 130 to 140 FPS in that scene. Swapping to Proton‑GE with ntsync raised that to roughly 135 to 144 FPS. The gains are not huge in pure numbers, but the frame rate was a bit more stable, spending more time at the higher end of that range.
For a fast 60 Hz shooter, the subjective difference is more about frame time consistency than raw FPS, and the early impression is that Modern Warfare feels at least as good and slightly smoother on the beta, not worse.
Call of Duty: Black Ops
The most compelling report so far comes from the Steam Deck subreddit. A user who had been playing the original Call of Duty: Black Ops described “horrendous framerate drops” and occasional “glitchy or pitch black” objects when running the game with fsync under older SteamOS builds.
On 3.7.20, using Proton‑GE with ntsync, they report that these issues are “completely” gone. The game no longer dives into slideshow territory during heavy moments, and the rendering glitches clear up. They describe it not as a minor uplift but as a night‑and‑day improvement for playability.
Black Ops is exactly the kind of game that strains synchronization on Proton. Its engine is pushing a lot of scripted AI, particles and physics at once in campaign set pieces, and its multiplayer code predates modern PC threading expectations. The fact that ntsync can both stabilize frame rate and resolve visual oddities there is an encouraging sign.
Other legacy shooters and Windows titles
Outside Call of Duty, the broader Linux and Steam Deck community has already seen ntsync pay off for various older games on desktop Linux distributions, particularly finicky Unreal Engine 3 titles and some source‑era shooters. Early Steam Deck‑specific coverage from outlets like SteamDeckHQ and GamingOnLinux echoes the same general message: this is not a universal performance miracle, but a highly targeted fix that can significantly help the right kinds of games.
Most modern titles that already run well under fsync are not seeing dramatic changes in early testing. The value of 3.7.20 is mostly concentrated in older Windows games that were showing odd stutters, uneven frame pacing or unexplained CPU bottlenecks.
How to try ntsync with classic Call of Duty on Steam Deck
If you are curious to see what ntsync does for your own library, the process is straightforward and reversible.
First, opt into the SteamOS beta or preview channel on your Deck. From Gaming Mode, open Settings, then System, then change the System Update Channel to Beta or Preview. Let the system download and install SteamOS 3.7.20, then reboot when prompted.
Next, you will want a Proton build that actually uses ntsync. Right now the easiest path is Proton‑GE. Switch your Deck into Desktop Mode, open the Discover app store and search for ProtonUp‑Qt. Install it, run it and tell it to add the latest Proton‑GE release to your Steam compatibility tools.
Once that is installed, go back to Gaming Mode, find the Call of Duty you want to test in your library and open its properties. Under Compatibility, enable “Force the use of a specific Steam Play compatibility tool,” then pick the Proton‑GE version you just installed.
After that, launch the game as normal. Under the hood, Proton‑GE should take advantage of the new ntsync driver now present in the SteamOS 3.7.20 kernel.
If you care about frame time graphs, enable the Deck’s performance overlay at level 3 or higher and watch both frame rate and frame time stability during busy scenes, not just in quiet corridors.
If a specific game behaves worse, you can simply switch that title back to a standard Proton release or even drop your Deck’s system channel back to Stable through the same Settings menu you used earlier.
Should you opt into the SteamOS 3.7.20 beta for older shooters?
Whether to jump into a beta system update always comes down to how much you value a specific improvement compared with the risk of new bugs. For 3.7.20, that trade‑off is especially relevant if your Deck is mostly a classic multiplayer shooter box.
If you mainly play classic Call of Duty campaigns and private matches, 3.7.20 is worth a serious look. Based on current data, Modern Warfare sees small but real stability gains, and Black Ops makes a much bigger leap from borderline to comfortable. If you have struggled with stutter, weird dips or visual artifacts in these games on SteamOS, the combination of 3.7.20 and Proton‑GE is your best shot yet at cleaning them up without dual‑booting Windows.
If you hop between a lot of modern games and your library runs smoothly today, the upsides are more limited. Most newer shooters and contemporary titles are not showing dramatic improvements in early testing, and the beta label always carries some risk. That said, this particular update is relatively low‑impact outside of ntsync, so the chance of dramatic regressions appears smaller than on feature‑heavy firmware updates.
If you rely on your Deck for competitive multiplayer in games with strict anti‑cheat, remember that ntsync does not change the compatibility story for modern kernel‑level anti‑cheats that simply do not support Proton or Linux. Those games will still require Windows regardless of what SteamOS does at the kernel synchronization layer.
For players who largely live in older Windows shooters that have been “almost great” on Deck, SteamOS 3.7.20 feels like a targeted quality‑of‑life update. It tightens up a specific weakness in Proton’s stack rather than chasing headline‑grabbing new features.
Practical advice if your focus is legacy multiplayer
If you are on the fence and your goal is the best possible experience for older multiplayer shooters, a cautious but proactive approach makes sense.
Consider opting one Deck into the beta if you have multiple devices, or set aside some time to test a handful of games that have historically been rough for you. Start with the problematic titles such as Call of Duty 4 and Black Ops, a couple of other older shooters in your library and maybe an Unreal Engine 3 game or two if you own any.
Pay attention not just to peak FPS but to how consistent the experience feels during big firefights and explosive set pieces. If your worst offenders suddenly behave like normal games and nothing else breaks, staying on the beta or preview channel until 3.7.20 goes stable is a reasonable choice.
If you see no benefit and are nervous about being on a test channel, it is easy to revert SteamOS to the Stable update channel. Your Proton‑GE installs will stick around, so you can still benefit from non‑ntsync improvements there while waiting for Valve to roll ntsync into a future stable SteamOS release.
For now, the story of SteamOS 3.7.20 on Steam Deck is simple. It does not radically redefine what the hardware can play, but for a very specific slice of the library, especially classic Call of Duty, it smooths over enough rough edges that a Sunday spent tinkering with Proton‑GE and the beta channel is finally worth it.