diff --git a/.changeset/session-minter-oiat-type.md b/.changeset/session-minter-oiat-type.md
new file mode 100644
index 00000000000..860ee52193c
--- /dev/null
+++ b/.changeset/session-minter-oiat-type.md
@@ -0,0 +1,5 @@
+---
+'@clerk/shared': patch
+---
+
+Add `oiat` (original_issued_at) field to `JwtHeader` type for Session Minter monotonic token freshness checks.
diff --git a/packages/shared/src/types/jwtv2.ts b/packages/shared/src/types/jwtv2.ts
index f03d6738333..1d8af24d979 100644
--- a/packages/shared/src/types/jwtv2.ts
+++ b/packages/shared/src/types/jwtv2.ts
@@ -25,6 +25,8 @@ export interface JwtHeader {
   'x5t#S256'?: string;
   x5t?: string;
   x5c?: string | string[];
+  /** @internal - used by Session Minter for monotonic token freshness checks. Do not depend on this field. */
+  oiat?: number;
 }
 
 declare global {