You updated the NVIDIA driver, launched a Direct3D 12 game through Steam Play, and the Reflex toggle is missing or greyed out. NVIDIA's 615.78.08 Linux driver adds VK_NV_low_latency2 revision 3, but a new driver alone does not put a Reflex option in your game. This checklist helps you find out whether the driver, Proton or the game is the missing piece, in order, before you change anything else.
According to Phoronix's report, the 615.78.08 build adds that extension revision to improve VKD3D-Proton. The report does not say which Proton, VKD3D-Proton or dxvk-nvapi versions pair with it, and neither does this guide. Check anything marked "verify" against NVIDIA's release notes and the upstream project docs before you rely on it.
The author has not run any of the commands below. Treat every one as untested, read the expected output as a description of what to look for, and adapt paths to your setup.
Prerequisites checklist
Work through these before you touch launch options.
- Distro and driver packaging (verify). Confirm that your distribution ships the 615.78.08 build or a newer one. Packaged drivers often lag NVIDIA's release by days or weeks. Check NVIDIA's release notes for the supported GPU list and kernel requirements.
- Driver version (verify against release notes). The driver named in the news is 615.78.08. Confirm in the release notes whether later releases keep the same behavior.
- Vulkan extension exposure. The driver must advertise VK_NV_low_latency2. This is the hard gate, and Step 2 below checks it.
- Proton build (verify). You need a Proton build whose bundled VKD3D-Proton and NVAPI layer (dxvk-nvapi) support the low-latency path. Find the minimum versions in the Proton, VKD3D-Proton and dxvk-nvapi release notes on GitHub. This article does not state them because Phoronix's report does not.
- Game support. The game must be a Direct3D 12 title that ships a Reflex option. A game without a Reflex integration will not gain one because your driver is new.
- GPU generation (verify). Confirm in NVIDIA's documentation that your GPU supports Reflex-style low latency. Do not assume older cards qualify.
Step 1: Confirm the installed driver version
The kernel module and the userspace libraries must match. A mismatch after an update without a reboot is a common reason new features appear to be missing.
nvidia-smi --query-gpu=driver_version --format=csv,noheader
cat /proc/driver/nvidia/version
Untested. The first command should print a single version string. The second should show the loaded kernel module version. If the two differ, or nvidia-smi reports a driver/library mismatch, reboot before going further.
Step 2: Check that Vulkan exposes VK_NV_low_latency2
If vulkaninfo is missing, install your distro's Vulkan tools package. The package name varies by distribution.
vulkaninfo --summary
vulkaninfo 2>/dev/null | grep -i low_latency
Untested. The summary should list your NVIDIA GPU as a physical device using the proprietary driver. The grep should return a line naming VK_NV_low_latency2, possibly with a spec revision number. Compare that number against what the release notes describe.
If nothing prints, Vulkan may be loading a different driver, such as an open-source one. The installed NVIDIA build may also predate the extension.
On hybrid laptops, run the check on the same GPU the game uses. PRIME offload variables differ by distro, so look them up in your distribution's NVIDIA documentation.
Step 3: Check which Proton build you are running
Open the game's Properties in Steam, go to Compatibility, and note the selected tool. Official builds live in your Steam library folder under steamapps/common. Community builds such as Proton-GE sit in a compatibilitytools.d directory inside your Steam root. Flatpak Steam uses different paths. For more on this, see read about how to check your amd p-state driver mode on linux.
ls "$HOME/.steam/steam/steamapps/common" | grep -i proton
cat "$HOME/.steam/steam/steamapps/common/<Proton folder>/version"
Untested, and the paths are assumptions. Expect a folder listing and a version file containing a build identifier. Then read that Proton release's notes to see which VKD3D-Proton and dxvk-nvapi versions it bundles. Compare them with the upstream minimums you found in the prerequisites.
Step 4: Set launch options, only if the docs require them
Some setups need NVAPI enabled explicitly in Proton. PROTON_ENABLE_NVAPI=1 is commonly used for this. Verify it against the current Proton documentation, because newer builds may enable NVAPI by default or handle it per game.
PROTON_ENABLE_NVAPI=1 %command%
Untested. Paste it into the game's Properties under General, then Launch Options. Add one variable at a time. If you stack options copied from forum threads, you cannot tell which one helped or broke the game.
Whether the low-latency path needs any VKD3D-Proton option is also a verify-against-source item. Check the VKD3D-Proton README and release notes rather than guessing.
Step 5: Confirm the in-game toggle and that it is active
Launch the game and open the graphics or display settings. Look for NVIDIA Reflex, often with options such as Off, On and On + Boost. Naming differs between games. See full coverage of rocm or vulkan for llama.cpp on amd gpus? how to decide for additional background.
A visible, selectable toggle is the first sign the game detected a capable driver and NVAPI layer. It does not prove the low-latency path is running.
For stronger evidence, enable logging for one session.
PROTON_LOG=1 %command%
Untested. After you quit, Proton should write a steam-<appid>.log file in your home directory. Search it for NVAPI and low-latency or latency-related messages. Which strings appear depends on the build, so check the upstream docs for what a healthy log looks like. Remove PROTON_LOG afterward, since logs grow large.
Troubleshooting and rollback
| Symptom | Likely cause | What to try | | --- | --- | --- | | Reflex toggle missing | Extension not exposed, NVAPI not active, or the game lacks Reflex | Redo Step 2, confirm the game supports Reflex, then try a newer Proton build | | Toggle greyed out | Wrong GPU in use, or an unsupported GPU | Check the active Vulkan device and NVIDIA's supported-hardware notes | | Crash on launch | Driver/Proton mismatch or a conflicting launch option | Clear launch options, then switch Proton versions | | Stutter or regression after update | New driver or VKD3D-Proton behavior | Roll back the driver or Proton build, then report upstream | | Driver reports library mismatch | Update without a reboot | Reboot, then rerun Step 1 |
Remove launch options
Open the game's Properties in Steam, clear the Launch Options field, and relaunch. This is the cheapest rollback, so do it first.
Also read: related topic: check storage layout before upgrading a proxy contract
Revert Proton
In Properties, go to Compatibility, tick the forced compatibility tool option, and choose the earlier Proton build you know worked. You can delete community builds from compatibilitytools.d, and Steam will fall back to its default.
Avoid deleting the game's compatdata prefix unless you must. Back it up first, because it holds saves and settings for some titles.
Revert the driver
The method depends on your distro, so follow its documentation. Ubuntu and Debian users can pin an older package from the repository or a PPA. Fedora users on RPM Fusion can downgrade through dnf. Arch and Manjaro users can reinstall earlier packages from the pacman cache or the Arch Linux Archive. All of these methods are untested.
Reinstall the matching kernel module packages, rebuild initramfs if your distro requires it, and reboot. Then rerun Step 1 to confirm the version.
What to expect next
Driver support is only one of three layers. Proton builds need to bundle matching VKD3D-Proton and dxvk-nvapi releases, and each game decides whether to offer Reflex at all. Watch the release notes for those projects over the coming weeks. Change one component at a time so you can tell which update made the difference.
