diff --git a/helper/Cargo.toml b/helper/Cargo.toml
index 34feb99..0c7741b 100644
--- a/helper/Cargo.toml
+++ b/helper/Cargo.toml
@@ -10,13 +10,14 @@ repository = "https://github.com/Cuprate/cuprate/tree/main/consensus"
 
 [features]
 # All features on by default.
-default = ["std", "atomic", "asynch", "num", "time", "thread"]
-std     = []
-atomic  = ["dep:crossbeam"]
-asynch  = ["dep:futures", "dep:rayon"]
-num     = []
-time    = ["dep:chrono", "std"]
-thread  = ["std", "dep:target_os_lib"]
+default   = ["std", "atomic", "asynch", "num", "time", "thread", "constants"]
+std       = []
+atomic    = ["dep:crossbeam"]
+asynch    = ["dep:futures", "dep:rayon"]
+constants = []
+num       = []
+time      = ["dep:chrono", "std"]
+thread    = ["std", "dep:target_os_lib"]
 
 [dependencies]
 crossbeam = { workspace = true, optional = true }
diff --git a/helper/build.rs b/helper/build.rs
new file mode 100644
index 0000000..709db42
--- /dev/null
+++ b/helper/build.rs
@@ -0,0 +1,32 @@
+fn main() {
+    #[cfg(feature = "constants")]
+    set_commit_env();
+}
+
+#[cfg(feature = "constants")]
+/// This sets the git `COMMIT` environment variable.
+fn set_commit_env() {
+    const PATH: &str = "../.git/refs/heads/";
+
+    println!("cargo:rerun-if-changed={PATH}");
+
+    // FIXME: This could also be `std::fs::read({PATH}/{branch})`
+    // so the machine building doesn't need `git`, although:
+    // 1. Having `git` as a build dependency is probably ok
+    // 2. It causes issues on PRs that aren't the `main` branch
+    let output = std::process::Command::new("git")
+        .arg("rev-parse")
+        .arg("HEAD")
+        .output()
+        .unwrap();
+
+    let commit = std::str::from_utf8(&output.stdout)
+        .unwrap()
+        .trim()
+        .to_lowercase();
+
+    // Commit hash should always be 40 bytes long.
+    assert_eq!(commit.as_bytes().len(), 40);
+
+    println!("cargo:rustc-env=COMMIT={commit}");
+}
diff --git a/helper/src/constants.rs b/helper/src/constants.rs
new file mode 100644
index 0000000..ca8c3dc
--- /dev/null
+++ b/helper/src/constants.rs
@@ -0,0 +1,22 @@
+//! General `const`ants and `static`s.
+//!
+//! `#[no_std]` compatible.
+
+//---------------------------------------------------------------------------------------------------- Use
+/// The current commit hash of the root Cuprate repository.
+///
+/// # Case & length
+/// It is guaranteed that `COMMIT` will be:
+/// - Lowercase
+/// - 40 characters long (no newline)
+///
+/// ```rust
+/// # use cuprate_helper::constants::*;
+/// assert_eq!(COMMIT.as_bytes().len(), 40);
+/// assert_eq!(COMMIT.to_lowercase(), COMMIT);
+/// ```
+pub const COMMIT: &str = core::env!("COMMIT"); // Set in `helper/build.rs`.
+
+//---------------------------------------------------------------------------------------------------- Tests
+#[cfg(test)]
+mod test {}
diff --git a/helper/src/lib.rs b/helper/src/lib.rs
index fe118bb..1bd87c4 100644
--- a/helper/src/lib.rs
+++ b/helper/src/lib.rs
@@ -36,13 +36,21 @@
 //---------------------------------------------------------------------------------------------------- Public API
 #[cfg(feature = "asynch")]
 pub mod asynch; // async collides
+
 #[cfg(feature = "atomic")]
 pub mod atomic;
+
+#[cfg(feature = "constants")]
+pub mod constants;
+
 pub mod network;
+
 #[cfg(feature = "num")]
 pub mod num;
+
 #[cfg(feature = "thread")]
 pub mod thread;
+
 #[cfg(feature = "time")]
 pub mod time;