diff --git a/lib/addons/prebid/analytics.test.ts b/lib/addons/prebid/analytics.test.ts
index d519b83b..379ab7b2 100644
--- a/lib/addons/prebid/analytics.test.ts
+++ b/lib/addons/prebid/analytics.test.ts
@@ -155,6 +155,22 @@ describe("OptablePrebidAnalytics", () => {
       analytics = new OptablePrebidAnalytics(mockOptableInstance);
     });
 
+    describe("sessionDepth", () => {
+      const emptyAuction = { auctionId: "depth-auction", bidderRequests: [] };
+
+      // sessionStorage stringifies on write, so the stored depth reads back as
+      // a string while the fallback is a number. Consumers see one field.
+      it("is a number whether or not the session has a stored depth", async () => {
+        sessionStorage.removeItem("optableSessionDepth");
+        const unset = await analytics.toWitness(emptyAuction, []);
+        expect(unset.sessionDepth).toBe(1);
+
+        sessionStorage.optableSessionDepth = "4";
+        const stored = await analytics.toWitness(emptyAuction, []);
+        expect(stored.sessionDepth).toBe(4);
+      });
+    });
+
     describe("page config", () => {
       const emptyAuction = { auctionId: "page-auction", bidderRequests: [] };
 
diff --git a/lib/addons/prebid/analytics.ts b/lib/addons/prebid/analytics.ts
index 12c1fd8d..fbb617b6 100644
--- a/lib/addons/prebid/analytics.ts
+++ b/lib/addons/prebid/analytics.ts
@@ -646,7 +646,7 @@ class OptablePrebidAnalytics {
       userAgent: Bowser.parse(window.navigator.userAgent) as unknown as Record<string, any>,
       device,
       prebidjsVersion: this.prebidInstance?.version || "unknown",
-      sessionDepth: sessionStorage?.optableSessionDepth || 1,
+      sessionDepth: Number(sessionStorage?.optableSessionDepth) || 1,
       pageAuctionsCount: (window as any).optable?.pageAuctionsCount || 1,
       originSlug: this.optableInstance?.dcn?.site || (window as any).optable?.site || "unknown",
     };
diff --git a/lib/addons/prototypes/analytics.js b/lib/addons/prototypes/analytics.js
index 945edd09..b5e8524d 100644
--- a/lib/addons/prototypes/analytics.js
+++ b/lib/addons/prototypes/analytics.js
@@ -409,7 +409,7 @@ class OptablePrebidAnalytics {
         tenant: this.config.tenant,
         optableWrapperVersion: SDK_WRAPPER_VERSION, // eslint-disable-line no-undef
         prebidjsVersion: this.prebidInstance?.version || "unknown",
-        sessionDepth: sessionStorage?.optableSessionDepthIndex || 1,
+        sessionDepth: Number(sessionStorage?.optableSessionDepthIndex) || 1,
         pageAuctionsCount: window.optable?.pageAuctionIndex || 1,
         originSlug: window.optable?.site || this.optableInstance?.dcn?.site || "unknown", // optable.site first since dcn is analytics always
       };
diff --git a/lib/addons/prototypes/analytics.test.js b/lib/addons/prototypes/analytics.test.js
index 8abf5694..056344c2 100644
--- a/lib/addons/prototypes/analytics.test.js
+++ b/lib/addons/prototypes/analytics.test.js
@@ -138,6 +138,21 @@ describe("cache state", () => {
   });
 });
 
+describe("sessionDepth", () => {
+  // sessionStorage stringifies on write, so the stored depth reads back as a
+  // string while the fallback is a number. Consumers see one field.
+  test("is a number whether or not the session has a stored depth", async () => {
+    const { analytics, witness } = makeAnalytics();
+    sessionStorage.removeItem("optableSessionDepthIndex");
+    const unset = await run(analytics, witness, { bidderRequests: [bidderRequest("a", [])] });
+    expect(unset.sessionDepth).toBe(1);
+
+    sessionStorage.optableSessionDepthIndex = "4";
+    const stored = await run(analytics, witness, { bidderRequests: [bidderRequest("a", [])] });
+    expect(stored.sessionDepth).toBe(4);
+  });
+});
+
 describe("page config", () => {
   test("sent on the first auction of the page only", async () => {
     const { analytics, witness } = makeAnalytics();