diff --git a/crates/ty/docs/cli.md b/crates/ty/docs/cli.md
index 4df73846cbdb1..ac26903b0005f 100644
--- a/crates/ty/docs/cli.md
+++ b/crates/ty/docs/cli.md
@@ -63,7 +63,10 @@ ty check [OPTIONS] [PATH]...
 <p>ty will search in the resolved environments's <code>site-packages</code> directories for type information and third-party imports.</p>
 </dd><dt id="ty-check--python-platform"><a href="#ty-check--python-platform"><code>--python-platform</code></a>, <code>--platform</code> <i>platform</i></dt><dd><p>Target platform to assume when resolving types.</p>
 <p>This is used to specialize the type of <code>sys.platform</code> and will affect the visibility of platform-specific functions and attributes. If the value is set to <code>all</code>, no assumptions are made about the target platform. If unspecified, the current system's platform will be used.</p>
-</dd><dt id="ty-check--python-version"><a href="#ty-check--python-version"><code>--python-version</code></a>, <code>--target-version</code> <i>version</i></dt><dd><p>Python version to assume when resolving types</p>
+</dd><dt id="ty-check--python-version"><a href="#ty-check--python-version"><code>--python-version</code></a>, <code>--target-version</code> <i>version</i></dt><dd><p>Python version to assume when resolving types.</p>
+<p>The Python version affects allowed syntax, type definitions of the standard library, and type definitions of first- and third-party modules that are conditional on the Python version.</p>
+<p>By default, the Python version is inferred as the lower bound of the project's <code>requires-python</code> field from the <code>pyproject.toml</code>, if available. Otherwise, the latest stable version supported by ty is used, which is currently 3.13.</p>
+<p>ty will not infer the Python version from the Python environment at this time.</p>
 <p>Possible values:</p>
 <ul>
 <li><code>3.7</code></li>
diff --git a/crates/ty/src/args.rs b/crates/ty/src/args.rs
index be65581580bf7..9321319fad4ce 100644
--- a/crates/ty/src/args.rs
+++ b/crates/ty/src/args.rs
@@ -77,6 +77,15 @@ pub(crate) struct CheckCommand {
     pub(crate) extra_search_path: Option<Vec<SystemPathBuf>>,
 
     /// Python version to assume when resolving types.
+    ///
+    /// The Python version affects allowed syntax, type definitions of the standard library, and
+    /// type definitions of first- and third-party modules that are conditional on the Python version.
+    ///
+    /// By default, the Python version is inferred as the lower bound of the project's
+    /// `requires-python` field from the `pyproject.toml`, if available. Otherwise, the latest
+    /// stable version supported by ty is used, which is currently 3.13.
+    ///
+    /// ty will not infer the Python version from the Python environment at this time.
     #[arg(long, value_name = "VERSION", alias = "target-version")]
     pub(crate) python_version: Option<PythonVersion>,
 
diff --git a/crates/ty_test/src/config.rs b/crates/ty_test/src/config.rs
index 8bcaef829b3a6..316a3e502692e 100644
--- a/crates/ty_test/src/config.rs
+++ b/crates/ty_test/src/config.rs
@@ -57,6 +57,15 @@ impl MarkdownTestConfig {
 #[serde(rename_all = "kebab-case", deny_unknown_fields)]
 pub(crate) struct Environment {
     /// Target Python version to assume when resolving types.
+    ///
+    /// The Python version affects allowed syntax, type definitions of the standard library, and
+    /// type definitions of first- and third-party modules that are conditional on the Python version.
+    ///
+    /// By default, the Python version is inferred as the lower bound of the project's
+    /// `requires-python` field from the `pyproject.toml`, if available. Otherwise, the latest
+    /// stable version supported by ty is used, which is currently 3.13.
+    ///
+    /// ty will not infer the Python version from the Python environment at this time.
     pub(crate) python_version: Option<PythonVersion>,
 
     /// Target platform to assume when resolving types.