diff --git a/changelog.d/10643-webcrypto-method-identity.md b/changelog.d/10643-webcrypto-method-identity.md
new file mode 100644
index 0000000000..2a127a7cbf
--- /dev/null
+++ b/changelog.d/10643-webcrypto-method-identity.md
@@ -0,0 +1,3 @@
+### Fixed
+
+- `globalThis.crypto.randomUUID`, `.getRandomValues`, and `crypto.subtle`'s KEM methods (`encapsulateBits`/`decapsulateBits`/`encapsulateKey`/`decapsulateKey`) now have a stable identity across reads (`crypto.randomUUID === crypto.randomUUID` is `true`) instead of allocating a fresh closure on every property access.
diff --git a/crates/perry-runtime/src/object/global_this/ctor_thunks.rs b/crates/perry-runtime/src/object/global_this/ctor_thunks.rs
index 2468db130b..cb50412369 100644
--- a/crates/perry-runtime/src/object/global_this/ctor_thunks.rs
+++ b/crates/perry-runtime/src/object/global_this/ctor_thunks.rs
@@ -382,6 +382,16 @@ pub(crate) extern "C" fn cryptokey_usages_getter_thunk(
     cryptokey_property_getter(b"usages")
 }
 
+/// #10427: `globalThis.crypto.<method>` is a property READ, resolved fresh
+/// on every access through `vt_get_own_field` (there is no real `ObjectHeader`
+/// backing `globalThis.crypto` for the read to land an own slot on — see
+/// `crypto.webcrypto`'s NATIVE_MODULE_CLASS_ID namespace). Plain
+/// `js_closure_alloc` mints a brand-new `ClosureHeader` on every call, so
+/// `crypto.randomUUID === crypto.randomUUID` was `false` and every read
+/// allocated. `js_closure_alloc_singleton` (the same func-ptr-keyed cache PR
+/// #10630 traced the closure-identity contract back to) returns the SAME
+/// closure for the same `func_ptr` every time — the func_ptr IS the method
+/// identity here since these thunks take no captures.
 pub(crate) fn webcrypto_method_value(property_name: &str) -> Option<f64> {
     let (func_ptr, arity) = match property_name {
         "getRandomValues" => (webcrypto_get_random_values_thunk as *const u8, 1),
@@ -389,7 +399,7 @@ pub(crate) fn webcrypto_method_value(property_name: &str) -> Option<f64> {
         _ => return None,
     };
     crate::closure::js_register_closure_arity(func_ptr, arity);
-    let closure = crate::closure::js_closure_alloc(func_ptr, 0);
+    let closure = crate::closure::js_closure_alloc_singleton(func_ptr);
     if closure.is_null() {
         return Some(f64::from_bits(crate::value::TAG_UNDEFINED));
     }
@@ -408,10 +418,14 @@ fn subtle_crypto_method_spec(property_name: &str) -> Option<(*const u8, u32)> {
     }
 }
 
+/// Same per-read allocation defect as `webcrypto_method_value` above, for
+/// `crypto.subtle`'s KEM methods (`encapsulateBits` and friends — the rest of
+/// SubtleCrypto's surface is already cached via `bound_native_callable_export_value`,
+/// see #10427's PR body for which paths were and weren't affected).
 pub(crate) fn subtle_crypto_method_value(property_name: &str) -> Option<f64> {
     let (func_ptr, length) = subtle_crypto_method_spec(property_name)?;
     crate::closure::js_register_closure_rest(func_ptr, 0);
-    let closure = crate::closure::js_closure_alloc(func_ptr, 0);
+    let closure = crate::closure::js_closure_alloc_singleton(func_ptr);
     if closure.is_null() {
         return Some(f64::from_bits(crate::value::TAG_UNDEFINED));
     }
diff --git a/test-files/test_gap_10427_webcrypto_method_identity.ts b/test-files/test_gap_10427_webcrypto_method_identity.ts
new file mode 100644
index 0000000000..5571479eb6
--- /dev/null
+++ b/test-files/test_gap_10427_webcrypto_method_identity.ts
@@ -0,0 +1,61 @@
+// #10427: reading a Web Crypto method off `globalThis.crypto` (and
+// `crypto.subtle`) allocated a fresh closure on every access, so the method
+// had no stable identity (`crypto.randomUUID === crypto.randomUUID` was
+// `false`) and every read allocated. Root cause: `webcrypto_method_value` /
+// `subtle_crypto_method_value` in
+// crates/perry-runtime/src/object/global_this/ctor_thunks.rs called plain
+// `js_closure_alloc` instead of the func-ptr-keyed `js_closure_alloc_singleton`
+// cache. This covers every member of `globalThis.crypto` (`randomUUID`,
+// `getRandomValues`, `subtle` itself, and `subtle`'s methods including the
+// KEM pair that shared the same defect) plus `node:crypto`'s default import
+// as an already-correct control.
+import nodeCrypto from "node:crypto";
+import { randomBytes as namedRandomBytes, randomUUID as namedRandomUUID } from "node:crypto";
+
+// The issue's own repro, verbatim.
+console.log("randomUUID stable:", globalThis.crypto.randomUUID === globalThis.crypto.randomUUID);
+console.log("node:crypto randomUUID stable:", nodeCrypto.randomUUID === nodeCrypto.randomUUID);
+const seen = new Set();
+for (let i = 0; i < 3; i++) seen.add(globalThis.crypto.randomUUID);
+console.log("seen.size:", seen.size);
+
+// The other Web Crypto members the issue asked to check.
+console.log("getRandomValues stable:", globalThis.crypto.getRandomValues === globalThis.crypto.getRandomValues);
+console.log("crypto namespace stable:", globalThis.crypto === globalThis.crypto);
+console.log("subtle namespace stable:", globalThis.crypto.subtle === globalThis.crypto.subtle);
+console.log("crypto.subtle === crypto.subtle (2nd read pair):", crypto.subtle === crypto.subtle);
+
+// crypto.subtle's KEM methods went through the same broken per-read thunk as
+// randomUUID/getRandomValues.
+console.log("subtle.encapsulateBits stable:", crypto.subtle.encapsulateBits === crypto.subtle.encapsulateBits);
+console.log("subtle.decapsulateBits stable:", crypto.subtle.decapsulateBits === crypto.subtle.decapsulateBits);
+console.log("subtle.encapsulateKey stable:", crypto.subtle.encapsulateKey === crypto.subtle.encapsulateKey);
+console.log("subtle.decapsulateKey stable:", crypto.subtle.decapsulateKey === crypto.subtle.decapsulateKey);
+
+// Controls: subtle's other methods were already cached via a different
+// mechanism (bound_native_callable_export_value) — must stay stable too.
+console.log("subtle.digest stable:", crypto.subtle.digest === crypto.subtle.digest);
+console.log("subtle.encrypt stable:", crypto.subtle.encrypt === crypto.subtle.encrypt);
+console.log("subtle.generateKey stable:", crypto.subtle.generateKey === crypto.subtle.generateKey);
+
+// Cross-read identity: the SAME closure across DIFFERENT expressions that
+// resolve to the same property, not just repeated reads of one expression.
+const a = globalThis.crypto.randomUUID;
+const b = crypto.randomUUID;
+console.log("cross-read identity:", a === b);
+
+// node:crypto (module-level) default vs named import identity — already
+// correct before this fix; kept as a control so a future regression there
+// shows up in the same test.
+console.log("node:crypto default randomUUID === named randomUUID:", nodeCrypto.randomUUID === namedRandomUUID);
+console.log("node:crypto randomBytes stable:", nodeCrypto.randomBytes === nodeCrypto.randomBytes);
+console.log("node:crypto named randomBytes === default randomBytes:", namedRandomBytes === nodeCrypto.randomBytes);
+
+// Functional sanity: the cached closure still WORKS (shape check only — the
+// value itself is random, so no exact value is printed).
+const uuidPattern = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
+const u = globalThis.crypto.randomUUID();
+console.log("randomUUID() shape ok:", uuidPattern.test(u));
+console.log("randomUUID() distinct across calls:", globalThis.crypto.randomUUID() !== globalThis.crypto.randomUUID());
+const bytes = globalThis.crypto.getRandomValues(new Uint8Array(8));
+console.log("getRandomValues() length ok:", bytes.length === 8);