diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 21ed3f5..43d20af 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -62,7 +62,7 @@ jobs:
         uses: actions/download-artifact@v7
         with:
           name: package
-      - name: Build pexrc binary for all targets.
+      - name: Build pexrc binary.
         run: |
           chmod +x target/release/package
           export CARGO="$(command -v cargo)"
diff --git a/CHANGES.md b/CHANGES.md
index 00c552f..3c3de0e 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,12 @@
 # Release Notes
 
+## 0.15.0-unreleased
+
+This release adds defaults for Linux and Windows for the `platform_release` environment marker when
+generating platform details via `pexrc platform python <spec>`. Now the only `<unknown>` marker
+when using a spec is the `platform_version` which is actively antagonistic to any likely real-world
+use.
+
 ## 0.14.0
 
 This release adds `pexrc platform {info,python}` for displaying both local and foreign platform
diff --git a/Cargo.lock b/Cargo.lock
index e6a7368..6acef6b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2096,7 +2096,7 @@ dependencies = [
 
 [[package]]
 name = "pexrc"
-version = "0.14.0"
+version = "0.15.0-unreleased"
 dependencies = [
  "anstream",
  "anyhow",
diff --git a/Cargo.toml b/Cargo.toml
index 0b5856b..6aa75e7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,7 +5,7 @@ cargo-features = ["profile-rustflags"]
 
 [package]
 name = "pexrc"
-version = "0.14.0"
+version = "0.15.0-unreleased"
 edition = { workspace = true }
 publish = false
 
diff --git a/crates/python-platform/src/markers.rs b/crates/python-platform/src/markers.rs
index c36a8d2..63a3bf8 100644
--- a/crates/python-platform/src/markers.rs
+++ b/crates/python-platform/src/markers.rs
@@ -88,7 +88,12 @@ pub(crate) fn calculate(
         Cow::Owned(release.to_string())
     } else {
         match platform {
-            Platform::Linux(_) => Cow::Borrowed("<unknown>"),
+            Platform::Linux(_) => {
+                // At the time of writing this is the oldest Linux LTS kernel and a Civil
+                // Infrastructure Platform release; so seemingly a good backwards compatibility
+                // target.
+                Cow::Borrowed("4.4.302-cip103")
+            }
             Platform::Mac(Mac { release, .. }) => Cow::Owned(format!(
                 "{major}.{minor}.{patch}",
                 major = release.major,
diff --git a/crates/python-platform/src/os.rs b/crates/python-platform/src/os.rs
index 1a05e3e..fdfad56 100644
--- a/crates/python-platform/src/os.rs
+++ b/crates/python-platform/src/os.rs
@@ -10,7 +10,7 @@ use logging_timer::time;
 
 use crate::linux::LibcVersion;
 use crate::mac::Release as MacRelease;
-use crate::windows::Release as WindowsRelease;
+use crate::windows::{Release as WindowsRelease, Release};
 
 #[derive(Copy, Clone)]
 pub enum Libc {
@@ -98,7 +98,12 @@ impl FromStr for Os {
                 // This is macOS Big Sur from April 2021.
                 Ok(Self::Mac(MacRelease::new(11, 3)))
             }
-            "windows" => Ok(Self::Windows(None)),
+            "windows" => {
+                // We default to 10 ~arbitrarily. This does correspond to ~2014 (2015) though, like
+                // our Linux glibc default. Reasonably old backward compatiility for Windows, which,
+                // like Linux, is pretty great about not breaking backwards compatibility.
+                Ok(Self::Windows(Some(Release::Windows10)))
+            }
             value if let Some(version) = value.strip_prefix("macos_") => {
                 Ok(Self::Mac(MacRelease::parse(version, '_')?))
             }
diff --git a/src/commands/platform/python.rs b/src/commands/platform/python.rs
index 9d75b89..d39a62a 100644
--- a/src/commands/platform/python.rs
+++ b/src/commands/platform/python.rs
@@ -72,9 +72,9 @@ pub struct Python {
     /// + 3.14.5-windows
     ///
     /// When using these, defaults for each operating system are chosen:
-    /// + linux: glibc 2.17 & x86_64
+    /// + linux: 4.4.302-cip103 (January 2016) & glibc 2.17 (December 2012) & x86_64
     /// + macos: 11.3 (Big Sur April 2021) & aarch64
-    /// + windows: x86_64
+    /// + windows: 10 (first released July 2015) & x86_64
     ///
     /// Linux can be further refined by using the manylinux and musllinux standards; for example:
     /// + 3.14.5-manylinux1
@@ -90,7 +90,7 @@ pub struct Python {
     /// Windows can be further refined by specifying the release as well:
     /// + 3.14.5-windows_11
     ///
-    /// Finally, when specifying an operating system, an explicit chip architecture suffixe can be
+    /// Finally, when specifying an operating system, an explicit chip architecture suffix can be
     /// selected from among the following:
     /// + aarch64 (or arm64)
     /// + armv7 [^1]
@@ -105,11 +105,9 @@ pub struct Python {
     /// + cpython-3.14.5-windows_11-amd64
     ///
     /// [^1]: These chip architectures are only supported for Linux.
-    /// [^2]: The derived Python platform specification is complete save for two environment markers
-    ///       that appear to be unused in the wild:
-    ///       + platform_release: "<unknown>" unless macos_<release> or windows_<release> was
-    ///                           specified
-    ///       + platform_version: "<unknown>"
+    /// [^2]: The derived Python platform specification is complete save for the platform_release
+    ///       environment marker that appears to be unused in the wild. Its value is defaulted to
+    ///       "<unknown>".
     #[arg(value_parser = PythonPlatform::parse, verbatim_doc_comment)]
     python_platform: PythonPlatform,
 }