diff --git a/.changeset/internalize-jwt-decode-client.md b/.changeset/internalize-jwt-decode-client.md
new file mode 100644
index 000000000..745d9f8b6
--- /dev/null
+++ b/.changeset/internalize-jwt-decode-client.md
@@ -0,0 +1,5 @@
+---
+"@knocklabs/client": patch
+---
+
+Internalize `jwt-decode` in `@knocklabs/client` and drop the runtime dependency. Token decoding now uses a small inlined decoder, removing the package from consumers' install graphs.
diff --git a/packages/client/package.json b/packages/client/package.json
index 8809dea23..d3311d524 100644
--- a/packages/client/package.json
+++ b/packages/client/package.json
@@ -75,7 +75,6 @@
     "axios": "^1.15.1",
     "axios-retry": "^4.5.0",
     "eventemitter2": "^6.4.5",
-    "jwt-decode": "^4.0.0",
     "nanoid": "^3.3.12",
     "phoenix": "1.8.5",
     "urlpattern-polyfill": "^10.0.0"
diff --git a/packages/client/src/interfaces.ts b/packages/client/src/interfaces.ts
index 43baccad3..fdf065ab0 100644
--- a/packages/client/src/interfaces.ts
+++ b/packages/client/src/interfaces.ts
@@ -1,6 +1,6 @@
 import { GenericData } from "@knocklabs/types";
-import { JwtPayload } from "jwt-decode";
 
+import { JwtPayload } from "./jwt";
 import Knock from "./knock";
 
 export type LogLevel = "debug";
diff --git a/packages/client/src/jwt/index.ts b/packages/client/src/jwt/index.ts
new file mode 100644
index 000000000..714166aa2
--- /dev/null
+++ b/packages/client/src/jwt/index.ts
@@ -0,0 +1,83 @@
+/**
+ * Decodes a JWT payload by base64url-decoding the second segment and parsing
+ * it as JSON. This does not verify the token signature.
+ */
+
+export interface JwtPayload {
+  iss?: string;
+  sub?: string;
+  aud?: string | string[];
+  exp?: number;
+  nbf?: number;
+  iat?: number;
+  jti?: string;
+}
+
+export class InvalidTokenError extends Error {}
+InvalidTokenError.prototype.name = "InvalidTokenError";
+
+function b64DecodeUnicode(str: string): string {
+  return decodeURIComponent(
+    atob(str).replace(/(.)/g, (char) => {
+      let code = char.charCodeAt(0).toString(16).toUpperCase();
+      if (code.length < 2) {
+        code = "0" + code;
+      }
+      return "%" + code;
+    }),
+  );
+}
+
+function base64UrlDecode(str: string): string {
+  let output = str.replace(/-/g, "+").replace(/_/g, "/");
+  switch (output.length % 4) {
+    case 0:
+      break;
+    case 2:
+      output += "==";
+      break;
+    case 3:
+      output += "=";
+      break;
+    default:
+      throw new Error("base64 string is not of the correct length");
+  }
+
+  try {
+    return b64DecodeUnicode(output);
+  } catch {
+    return atob(output);
+  }
+}
+
+export function jwtDecode<T = JwtPayload>(token: string): T {
+  if (typeof token !== "string") {
+    throw new InvalidTokenError("Invalid token specified: must be a string");
+  }
+
+  // The payload is the second segment of the JWT (header.payload.signature).
+  const part = token.split(".")[1];
+
+  if (typeof part !== "string") {
+    throw new InvalidTokenError("Invalid token specified: missing part #2");
+  }
+
+  let decoded: string;
+  try {
+    decoded = base64UrlDecode(part);
+  } catch (e) {
+    const message = e instanceof Error ? e.message : String(e);
+    throw new InvalidTokenError(
+      `Invalid token specified: invalid base64 for part #2 (${message})`,
+    );
+  }
+
+  try {
+    return JSON.parse(decoded) as T;
+  } catch (e) {
+    const message = e instanceof Error ? e.message : String(e);
+    throw new InvalidTokenError(
+      `Invalid token specified: invalid json for part #2 (${message})`,
+    );
+  }
+}
diff --git a/packages/client/src/knock.ts b/packages/client/src/knock.ts
index d1f4648eb..06d881da4 100644
--- a/packages/client/src/knock.ts
+++ b/packages/client/src/knock.ts
@@ -1,5 +1,3 @@
-import { jwtDecode } from "jwt-decode";
-
 import ApiClient from "./api";
 import FeedClient from "./clients/feed";
 import MessageClient from "./clients/messages";
@@ -16,6 +14,7 @@ import {
   UserIdOrUserWithProperties,
   UserTokenExpiringCallback,
 } from "./interfaces";
+import { jwtDecode } from "./jwt";
 
 const DEFAULT_HOST = "https://api.knock.app";
 
diff --git a/packages/client/test/jwt.test.ts b/packages/client/test/jwt.test.ts
new file mode 100644
index 000000000..9b7355982
--- /dev/null
+++ b/packages/client/test/jwt.test.ts
@@ -0,0 +1,70 @@
+import { describe, expect, test } from "vitest";
+
+import { InvalidTokenError, jwtDecode } from "../src/jwt";
+
+// Builds a JWT-shaped string for the given payload. Only the payload segment
+// is meaningful to `jwtDecode`; the header and signature are placeholders.
+function encodeToken(payload: Record<string, unknown>): string {
+  const header = Buffer.from(
+    JSON.stringify({ alg: "HS256", typ: "JWT" }),
+  ).toString("base64url");
+  const body = Buffer.from(JSON.stringify(payload)).toString("base64url");
+  return `${header}.${body}.signature`;
+}
+
+describe("jwtDecode", () => {
+  test("decodes standard registered claims", () => {
+    const token = encodeToken({
+      sub: "user_123",
+      exp: 9999999999,
+      iat: 1516239022,
+    });
+
+    const decoded = jwtDecode(token);
+
+    expect(decoded.sub).toBe("user_123");
+    expect(decoded.exp).toBe(9999999999);
+    expect(decoded.iat).toBe(1516239022);
+  });
+
+  test("decodes custom claims via a type parameter", () => {
+    const token = encodeToken({ sub: "user_123", role: "admin" });
+
+    const decoded = jwtDecode<{ sub: string; role: string }>(token);
+
+    expect(decoded).toEqual({ sub: "user_123", role: "admin" });
+  });
+
+  test("decodes payloads containing unicode characters", () => {
+    const token = encodeToken({ name: "José Ünïcode 🚀" });
+
+    const decoded = jwtDecode<{ name: string }>(token);
+
+    expect(decoded.name).toBe("José Ünïcode 🚀");
+  });
+
+  test("decodes base64url payloads regardless of length (padding)", () => {
+    // Vary payload length to exercise each `length % 4` padding branch.
+    for (const id of ["a", "ab", "abc", "abcd"]) {
+      const decoded = jwtDecode<{ id: string }>(encodeToken({ id }));
+      expect(decoded.id).toBe(id);
+    }
+  });
+
+  test("throws InvalidTokenError when the token is not a string", () => {
+    // @ts-expect-error - exercising the runtime guard against non-string input
+    expect(() => jwtDecode(undefined)).toThrow(InvalidTokenError);
+  });
+
+  test("throws InvalidTokenError when the payload segment is missing", () => {
+    expect(() => jwtDecode("only-one-segment")).toThrow(InvalidTokenError);
+  });
+
+  test("throws InvalidTokenError when the payload is not valid JSON", () => {
+    const notJson = Buffer.from("not json").toString("base64url");
+
+    expect(() => jwtDecode(`header.${notJson}.signature`)).toThrow(
+      InvalidTokenError,
+    );
+  });
+});
diff --git a/packages/client/test/knock.test.ts b/packages/client/test/knock.test.ts
index 39d6f7f55..dd5660346 100644
--- a/packages/client/test/knock.test.ts
+++ b/packages/client/test/knock.test.ts
@@ -1,15 +1,15 @@
-import { jwtDecode } from "jwt-decode";
 import { afterEach, beforeEach, describe, expect, test, vi } from "vitest";
 
+import { jwtDecode } from "../src/jwt";
 import Knock from "../src/knock";
 
 import { authenticateKnock, createMockKnock } from "./test-utils/mocks";
 
 const TEST_BRANCH_SLUG = "lorem-ipsum-dolor-branch";
 
-// ✅ Mock the named export `jwtDecode` from the "jwt-decode" module.
+// ✅ Mock the named export `jwtDecode` from the internal jwt module.
 // It will always return a decoded token with an `exp` 61 seconds in the future.
-vi.mock("jwt-decode", () => ({
+vi.mock("../src/jwt", () => ({
   jwtDecode: vi.fn(() => ({
     exp: Math.floor(Date.now() / 1000) + 61,
   })),
diff --git a/yarn.lock b/yarn.lock
index cdcf61e41..4105814e9 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -4870,7 +4870,6 @@ __metadata:
     eslint: "npm:^8.56.0"
     eventemitter2: "npm:^6.4.5"
     jsonwebtoken: "npm:^9.0.3"
-    jwt-decode: "npm:^4.0.0"
     nanoid: "npm:^3.3.12"
     phoenix: "npm:1.8.5"
     prettier: "npm:^3.5.3"
@@ -15801,13 +15800,6 @@ __metadata:
   languageName: node
   linkType: hard
 
-"jwt-decode@npm:^4.0.0":
-  version: 4.0.0
-  resolution: "jwt-decode@npm:4.0.0"
-  checksum: 10c0/de75bbf89220746c388cf6a7b71e56080437b77d2edb29bae1c2155048b02c6b8c59a3e5e8d6ccdfd54f0b8bda25226e491a4f1b55ac5f8da04cfbadec4e546c
-  languageName: node
-  linkType: hard
-
 "keyv@npm:^4.5.3, keyv@npm:^4.5.4":
   version: 4.5.4
   resolution: "keyv@npm:4.5.4"