diff --git a/packages/core/package.json b/packages/core/package.json
index ccc5695f13..f2bf463a60 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -149,6 +149,7 @@
     }
   },
   "dependencies": {
+    "@opentelemetry/api": "^1.9.0",
     "@opentelemetry/semantic-conventions": "^1.39.0",
     "@standard-schema/spec": "^1.1.0",
     "zod": "^4.3.6"
@@ -169,7 +170,6 @@
   "peerDependencies": {
     "@better-auth/utils": "catalog:",
     "@better-fetch/fetch": "catalog:",
-    "@opentelemetry/api": "^1.9.0",
     "better-call": "catalog:",
     "@cloudflare/workers-types": ">=4",
     "jose": "^6.1.0",
diff --git a/packages/core/src/instrumentation/instrumentation.test.ts b/packages/core/src/instrumentation/instrumentation.test.ts
index cc7e40f98a..283a739081 100644
--- a/packages/core/src/instrumentation/instrumentation.test.ts
+++ b/packages/core/src/instrumentation/instrumentation.test.ts
@@ -8,6 +8,41 @@ import { afterAll, beforeAll, beforeEach, describe, expect, it } from "vitest";
 import { withSpan } from ".";
 import { ATTR_DB_COLLECTION_NAME, ATTR_DB_OPERATION_NAME } from "./attributes";
 
+/**
+ * @see https://github.com/better-auth/better-auth/issues/8765
+ */
+describe("withSpan no-op behavior (no SDK registered)", () => {
+	it("returns the value of a synchronous function", () => {
+		const result = withSpan("noop.sync", { attr: "value" }, () => 42);
+		expect(result).toBe(42);
+	});
+
+	it("returns the resolved value of an async function", async () => {
+		const result = await withSpan("noop.async", { attr: "value" }, async () => {
+			await new Promise((r) => setTimeout(r, 0));
+			return "async-noop";
+		});
+		expect(result).toBe("async-noop");
+	});
+
+	it("re-throws synchronous errors", () => {
+		expect(() =>
+			withSpan("noop.sync.throw", {}, () => {
+				throw new Error("noop-sync-error");
+			}),
+		).toThrow("noop-sync-error");
+	});
+
+	it("re-throws asynchronous errors", async () => {
+		await expect(
+			withSpan("noop.async.throw", {}, async () => {
+				await Promise.resolve();
+				throw new Error("noop-async-error");
+			}),
+		).rejects.toThrow("noop-async-error");
+	});
+});
+
 describe("instrumentation", () => {
 	let provider: NodeTracerProvider;
 	let exporter: InMemorySpanExporter;
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 1531294cfb..af0e5842d2 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -693,7 +693,7 @@ importers:
     devDependencies:
       '@cloudflare/vitest-pool-workers':
         specifier: ^0.12.18
-        version: 0.12.18(@cloudflare/workers-types@4.20260226.1)(@vitest/runner@4.1.3)(@vitest/snapshot@4.1.3)(vitest@4.1.3(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/coverage-istanbul@4.0.18(vitest@4.0.18))(@vitest/ui@4.0.18)(happy-dom@20.8.9)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3)))
+        version: 0.12.18(@cloudflare/workers-types@4.20260226.1)(@vitest/runner@4.1.3)(@vitest/snapshot@4.1.3)(vitest@4.1.3(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/coverage-istanbul@4.0.18(vitest@4.0.18))(@vitest/ui@4.0.18(vitest@4.0.18))(happy-dom@20.8.9)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3)))
       '@cloudflare/workers-types':
         specifier: ^4.20260226.1
         version: 4.20260226.1
@@ -1056,6 +1056,9 @@ importers:
 
   packages/core:
     dependencies:
+      '@opentelemetry/api':
+        specifier: ^1.9.0
+        version: 1.9.0
       '@opentelemetry/semantic-conventions':
         specifier: ^1.39.0
         version: 1.39.0
@@ -1075,9 +1078,6 @@ importers:
       '@cloudflare/workers-types':
         specifier: ^4.20250121.0
         version: 4.20260226.1
-      '@opentelemetry/api':
-        specifier: ^1.9.0
-        version: 1.9.0
       '@opentelemetry/sdk-trace-base':
         specifier: ^1.30.0
         version: 1.30.1(@opentelemetry/api@1.9.0)
@@ -16544,14 +16544,14 @@ snapshots:
     optionalDependencies:
       workerd: 1.20260305.0
 
-  '@cloudflare/vitest-pool-workers@0.12.18(@cloudflare/workers-types@4.20260226.1)(@vitest/runner@4.1.3)(@vitest/snapshot@4.1.3)(vitest@4.1.3(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/coverage-istanbul@4.0.18(vitest@4.0.18))(@vitest/ui@4.0.18)(happy-dom@20.8.9)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3)))':
+  '@cloudflare/vitest-pool-workers@0.12.18(@cloudflare/workers-types@4.20260226.1)(@vitest/runner@4.1.3)(@vitest/snapshot@4.1.3)(vitest@4.1.3(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/coverage-istanbul@4.0.18(vitest@4.0.18))(@vitest/ui@4.0.18(vitest@4.0.18))(happy-dom@20.8.9)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3)))':
     dependencies:
       '@vitest/runner': 4.1.3
       '@vitest/snapshot': 4.1.3
       cjs-module-lexer: 1.4.3
       esbuild: 0.27.3
       miniflare: 4.20260305.0
-      vitest: 4.1.3(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/coverage-istanbul@4.0.18(vitest@4.0.18))(@vitest/ui@4.0.18)(happy-dom@20.8.9)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3))
+      vitest: 4.1.3(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/coverage-istanbul@4.0.18(vitest@4.0.18))(@vitest/ui@4.0.18(vitest@4.0.18))(happy-dom@20.8.9)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3))
       wrangler: 4.69.0(@cloudflare/workers-types@4.20260226.1)
     transitivePeerDependencies:
       - '@cloudflare/workers-types'
@@ -21958,7 +21958,7 @@ snapshots:
       sirv: 3.0.2
       tinyglobby: 0.2.15
       tinyrainbow: 3.0.3
-      vitest: 4.0.18(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/ui@4.0.18)(happy-dom@20.8.9)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3)
+      vitest: 4.0.18(@opentelemetry/api@1.9.0)(@types/node@25.3.2)(@vitest/ui@4.0.18)(happy-dom@20.8.9)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(msw@2.12.10(@types/node@25.3.2)(typescript@5.9.3))(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3)
 
   '@vitest/utils@4.0.18':
     dependencies:
@@ -31300,7 +31300,7 @@ snapshots:
       - tsx
       - yaml
 
-  vitest@4.1.3(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/coverage-istanbul@4.0.18(vitest@4.0.18))(@vitest/ui@4.0.18)(happy-dom@20.8.9)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3)):
+  vitest@4.1.3(@opentelemetry/api@1.9.0)(@types/node@25.5.2)(@vitest/coverage-istanbul@4.0.18(vitest@4.0.18))(@vitest/ui@4.0.18(vitest@4.0.18))(happy-dom@20.8.9)(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3)):
     dependencies:
       '@vitest/expect': 4.1.3
       '@vitest/mocker': 4.1.3(msw@2.12.10(@types/node@25.5.2)(typescript@5.9.3))(vite@7.3.2(@types/node@25.5.2)(jiti@2.6.1)(less@4.5.1)(lightningcss@1.32.0)(sass@1.97.1)(terser@5.46.1)(tsx@4.21.0)(yaml@2.8.3))