diff --git a/Cargo.lock b/Cargo.lock
index 7e112128f..bfe188254 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -444,7 +444,7 @@ dependencies = [
  "http 0.2.12",
  "http 1.5.0",
  "percent-encoding",
- "sha2 0.11.0",
+ "sha2",
  "time",
  "tracing",
 ]
@@ -1896,7 +1896,7 @@ dependencies = [
  "rusqlite",
  "serde",
  "serde_json",
- "sha2 0.10.9",
+ "sha2",
  "tempfile",
  "thiserror 2.0.20",
  "tiktoken-rs",
@@ -1959,7 +1959,7 @@ dependencies = [
  "reqwest",
  "serde",
  "serde_json",
- "sha2 0.10.9",
+ "sha2",
  "thiserror 2.0.20",
  "tokio",
  "tokio-stream",
@@ -3962,17 +3962,6 @@ dependencies = [
  "digest 0.11.3",
 ]
 
-[[package]]
-name = "sha2"
-version = "0.10.9"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a7507d819769d01a365ab707794a4084392c824f54a7a6a7862f8c3d0892b283"
-dependencies = [
- "cfg-if",
- "cpufeatures 0.2.17",
- "digest 0.10.7",
-]
-
 [[package]]
 name = "sha2"
 version = "0.11.0"
diff --git a/crates/headroom-core/Cargo.toml b/crates/headroom-core/Cargo.toml
index c1f0d5537..903f4511f 100644
--- a/crates/headroom-core/Cargo.toml
+++ b/crates/headroom-core/Cargo.toml
@@ -28,7 +28,7 @@ hf-hub = { version = "0.5", default-features = false, features = ["ureq", "rustl
 md-5 = "0.10"
 # `sha2` for `_hash_field_name` in smart_crusher (SHA256 truncated to 16
 # hex chars). Python uses `hashlib.sha256` so we need byte-exact parity.
-sha2 = "0.10"
+sha2 = "0.11"
 # `dashmap` for the CCR storage backend. Concurrent HashMap with sharded
 # locking — distinct keys hashed to different shards never contend, so
 # multi-worker proxy load doesn't queue on a single Mutex. Lock-free
diff --git a/crates/headroom-core/src/rollout.rs b/crates/headroom-core/src/rollout.rs
index fc9d4fb92..1ff027413 100644
--- a/crates/headroom-core/src/rollout.rs
+++ b/crates/headroom-core/src/rollout.rs
@@ -323,7 +323,12 @@ pub fn feature_names() -> BTreeSet<&'static str> {
 
 fn digest_value(value: &Value) -> String {
     let canonical = serde_json::to_vec(value).expect("rollout provenance is serializable");
-    format!("sha256:{:x}", Sha256::digest(canonical))
+    let digest = Sha256::digest(canonical);
+    let mut hex = String::with_capacity(digest.len() * 2);
+    for byte in digest {
+        hex.push_str(&format!("{byte:02x}"));
+    }
+    format!("sha256:{hex}")
 }
 
 #[cfg(test)]
diff --git a/crates/headroom-core/src/transforms/smart_crusher/hashing.rs b/crates/headroom-core/src/transforms/smart_crusher/hashing.rs
index 2648639c5..437278bf1 100644
--- a/crates/headroom-core/src/transforms/smart_crusher/hashing.rs
+++ b/crates/headroom-core/src/transforms/smart_crusher/hashing.rs
@@ -28,7 +28,10 @@ pub fn hash_field_name(field_name: &str) -> String {
     let digest = hasher.finalize();
     // Truncate to first 8 hex chars (4 bytes of digest). MUST match
     // Python's `[:8]` — see module-level note above.
-    let hex = format!("{:x}", digest);
+    let mut hex = String::with_capacity(digest.len() * 2);
+    for byte in digest {
+        hex.push_str(&format!("{byte:02x}"));
+    }
     hex[..8].to_string()
 }
 
diff --git a/crates/headroom-proxy/Cargo.toml b/crates/headroom-proxy/Cargo.toml
index b1f5088f1..a2bf52f31 100644
--- a/crates/headroom-proxy/Cargo.toml
+++ b/crates/headroom-proxy/Cargo.toml
@@ -74,7 +74,7 @@ prometheus = { version = "=0.14.0", default-features = false }
 # `aws-smithy-runtime-api`); promoted here to a direct, normal-build
 # dependency so the drift detector compiles outside `cfg(test)`. Also
 # used by PR-E4 for `prompt_cache_key` derivation.
-sha2 = "0.10"
+sha2 = "0.11"
 # PR-E6: bounded session-scoped cache of structural hashes. The
 # detector evicts the oldest session at 1000 entries — we never want
 # unbounded memory growth from a flood of unique session keys. `lru`
@@ -110,7 +110,7 @@ tokio-stream = "0.1"
 # way to gate "the proxy did not perturb the request" because JSON
 # value-equality misses whitespace, key order, and Unicode escape
 # differences that all bust the prompt cache.
-sha2 = "0.10"
+sha2 = "0.11"
 # PR-C1: property tests for the byte-level SSE parser. The parser
 # must never panic on arbitrary input bytes (TCP can hand us anything,
 # including malformed UTF-8 split mid-codepoint or fuzz-generated