diff --git a/codex-rs/default.nix b/codex-rs/default.nix
index c9586128e6..fc7dd978ef 100644
--- a/codex-rs/default.nix
+++ b/codex-rs/default.nix
@@ -5,6 +5,7 @@
   rustPlatform,
   pkg-config,
   lib,
+  version ? "0.0.0",
   ...
 }:
 rustPlatform.buildRustPackage (_: {
@@ -12,10 +13,18 @@ rustPlatform.buildRustPackage (_: {
     PKG_CONFIG_PATH = "${openssl.dev}/lib/pkgconfig:$PKG_CONFIG_PATH";
   };
   pname = "codex-rs";
-  version = "0.1.0";
+  inherit version;
   cargoLock.lockFile = ./Cargo.lock;
   doCheck = false;
   src = ./.;
+
+  # Patch the workspace Cargo.toml so that cargo embeds the correct version in
+  # CARGO_PKG_VERSION (which the binary reads via env!("CARGO_PKG_VERSION")).
+  # On release commits the Cargo.toml already contains the real version and
+  # this sed is a no-op.
+  postPatch = ''
+    sed -i 's/^version = "0\.0\.0"$/version = "${version}"/' Cargo.toml
+  '';
   nativeBuildInputs = [
     cmake
     llvmPackages.clang
diff --git a/flake.nix b/flake.nix
index 711172d737..1fd41c6f14 100644
--- a/flake.nix
+++ b/flake.nix
@@ -9,7 +9,7 @@
     };
   };
 
-  outputs = { nixpkgs, rust-overlay, ... }:
+  outputs = { self, nixpkgs, rust-overlay, ... }:
     let
       systems = [
         "x86_64-linux"
@@ -18,6 +18,19 @@
         "aarch64-darwin"
       ];
       forAllSystems = f: nixpkgs.lib.genAttrs systems f;
+
+      # Read the version from the workspace Cargo.toml (the single source of
+      # truth used by the release workflow).
+      cargoToml = builtins.fromTOML (builtins.readFile ./codex-rs/Cargo.toml);
+      cargoVersion = cargoToml.workspace.package.version;
+
+      # When building from a release commit the Cargo.toml already carries the
+      # real version (e.g. "0.101.0").  On the main branch it is the placeholder
+      # "0.0.0", so we fall back to a dev version derived from the flake source.
+      version =
+        if cargoVersion != "0.0.0"
+        then cargoVersion
+        else "0.0.0-dev+${self.shortRev or "dirty"}";
     in
     {
       packages = forAllSystems (system:
@@ -27,6 +40,7 @@
             overlays = [ rust-overlay.overlays.default ];
           };
           codex-rs = pkgs.callPackage ./codex-rs {
+            inherit version;
             rustPlatform = pkgs.makeRustPlatform {
               cargo = pkgs.rust-bin.stable.latest.minimal;
               rustc = pkgs.rust-bin.stable.latest.minimal;