diff --git a/.changeset/dark-sides-beg.md b/.changeset/dark-sides-beg.md
new file mode 100644
index 00000000000..857f265b835
--- /dev/null
+++ b/.changeset/dark-sides-beg.md
@@ -0,0 +1,5 @@
+---
+'@clerk/clerk-js': patch
+---
+
+Fix issue where `SignIn` and `SignUp` instances were unable to be serialized with `JSON.stringify` due to a circular reference.
diff --git a/packages/clerk-js/src/core/resources/SignIn.ts b/packages/clerk-js/src/core/resources/SignIn.ts
index 8888af69a0a..73f43de78e6 100644
--- a/packages/clerk-js/src/core/resources/SignIn.ts
+++ b/packages/clerk-js/src/core/resources/SignIn.ts
@@ -631,67 +631,71 @@ class SignInFuture implements SignInFutureResource {
     verifyBackupCode: this.verifyBackupCode.bind(this),
   };
 
-  constructor(readonly resource: SignIn) {}
+  readonly #resource: SignIn;
+
+  constructor(resource: SignIn) {
+    this.#resource = resource;
+  }
 
   get id() {
-    return this.resource.id;
+    return this.#resource.id;
   }
 
   get identifier() {
-    return this.resource.identifier;
+    return this.#resource.identifier;
   }
 
   get createdSessionId() {
-    return this.resource.createdSessionId;
+    return this.#resource.createdSessionId;
   }
 
   get userData() {
-    return this.resource.userData;
+    return this.#resource.userData;
   }
 
   get status() {
     // @TODO hooks-revamp: Consolidate this fallback val with stateProxy
-    return this.resource.status || 'needs_identifier';
+    return this.#resource.status || 'needs_identifier';
   }
 
   get supportedFirstFactors() {
-    return this.resource.supportedFirstFactors ?? [];
+    return this.#resource.supportedFirstFactors ?? [];
   }
 
   get supportedSecondFactors() {
-    return this.resource.supportedSecondFactors ?? [];
+    return this.#resource.supportedSecondFactors ?? [];
   }
 
   get isTransferable() {
-    return this.resource.firstFactorVerification.status === 'transferable';
+    return this.#resource.firstFactorVerification.status === 'transferable';
   }
 
   get existingSession() {
     if (
-      this.resource.firstFactorVerification.status === 'failed' &&
-      this.resource.firstFactorVerification.error?.code === 'identifier_already_signed_in' &&
-      this.resource.firstFactorVerification.error?.meta?.sessionId
+      this.#resource.firstFactorVerification.status === 'failed' &&
+      this.#resource.firstFactorVerification.error?.code === 'identifier_already_signed_in' &&
+      this.#resource.firstFactorVerification.error?.meta?.sessionId
     ) {
-      return { sessionId: this.resource.firstFactorVerification.error?.meta?.sessionId };
+      return { sessionId: this.#resource.firstFactorVerification.error?.meta?.sessionId };
     }
 
     return undefined;
   }
 
   get firstFactorVerification() {
-    return this.resource.firstFactorVerification;
+    return this.#resource.firstFactorVerification;
   }
 
   get secondFactorVerification() {
-    return this.resource.secondFactorVerification;
+    return this.#resource.secondFactorVerification;
   }
 
   async sendResetPasswordEmailCode(): Promise<{ error: ClerkError | null }> {
-    if (!this.resource.id) {
+    if (!this.#resource.id) {
       throw new Error('Cannot reset password without a sign in.');
     }
-    return runAsyncResourceTask(this.resource, async () => {
-      const resetPasswordEmailCodeFactor = this.resource.supportedFirstFactors?.find(
+    return runAsyncResourceTask(this.#resource, async () => {
+      const resetPasswordEmailCodeFactor = this.#resource.supportedFirstFactors?.find(
         f => f.strategy === 'reset_password_email_code',
       );
 
@@ -702,7 +706,7 @@ class SignInFuture implements SignInFutureResource {
       }
 
       const { emailAddressId } = resetPasswordEmailCodeFactor;
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { emailAddressId, strategy: 'reset_password_email_code' },
         action: 'prepare_first_factor',
       });
@@ -711,8 +715,8 @@ class SignInFuture implements SignInFutureResource {
 
   async verifyResetPasswordEmailCode(params: SignInFutureEmailCodeVerifyParams): Promise<{ error: ClerkError | null }> {
     const { code } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { code, strategy: 'reset_password_email_code' },
         action: 'attempt_first_factor',
       });
@@ -721,8 +725,8 @@ class SignInFuture implements SignInFutureResource {
 
   async submitResetPassword(params: SignInFutureResetPasswordSubmitParams): Promise<{ error: ClerkError | null }> {
     const { password, signOutOfOtherSessions = true } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { password, signOutOfOtherSessions },
         action: 'reset_password',
       });
@@ -731,14 +735,14 @@ class SignInFuture implements SignInFutureResource {
 
   private async _create(params: SignInFutureCreateParams): Promise<void> {
     const locale = getBrowserLocale();
-    await this.resource.__internal_basePost({
-      path: this.resource.pathRoot,
+    await this.#resource.__internal_basePost({
+      path: this.#resource.pathRoot,
       body: locale ? { locale, ...params } : params,
     });
   }
 
   async create(params: SignInFutureCreateParams): Promise<{ error: ClerkError | null }> {
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       await this._create(params);
     });
   }
@@ -748,13 +752,13 @@ class SignInFuture implements SignInFutureResource {
       throw new Error('Only one of identifier, emailAddress, or phoneNumber can be provided');
     }
 
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       // TODO @userland-errors:
       const identifier = params.identifier || params.emailAddress || params.phoneNumber;
-      const previousIdentifier = this.resource.identifier;
+      const previousIdentifier = this.#resource.identifier;
       const locale = getBrowserLocale();
-      await this.resource.__internal_basePost({
-        path: this.resource.pathRoot,
+      await this.#resource.__internal_basePost({
+        path: this.#resource.pathRoot,
         body: {
           identifier: identifier || previousIdentifier,
           password: params.password,
@@ -766,19 +770,19 @@ class SignInFuture implements SignInFutureResource {
 
   async sendEmailCode(params: SignInFutureEmailCodeSendParams = {}): Promise<{ error: ClerkError | null }> {
     const { emailAddress, emailAddressId } = params;
-    if (!this.resource.id && emailAddressId) {
+    if (!this.#resource.id && emailAddressId) {
       throw new Error(
         'signIn.emailCode.sendCode() cannot be called with an emailAddressId if an existing signIn does not exist.',
       );
     }
 
-    if (!this.resource.id && !emailAddress) {
+    if (!this.#resource.id && !emailAddress) {
       throw new Error(
         'signIn.emailCode.sendCode() cannot be called without an emailAddress if an existing signIn does not exist.',
       );
     }
 
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       if (emailAddress) {
         await this._create({ identifier: emailAddress });
       }
@@ -788,7 +792,7 @@ class SignInFuture implements SignInFutureResource {
         throw new ClerkRuntimeError('Email code factor not found', { code: 'factor_not_found' });
       }
 
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { emailAddressId: emailCodeFactor.emailAddressId, strategy: 'email_code' },
         action: 'prepare_first_factor',
       });
@@ -797,8 +801,8 @@ class SignInFuture implements SignInFutureResource {
 
   async verifyEmailCode(params: SignInFutureEmailCodeVerifyParams): Promise<{ error: ClerkError | null }> {
     const { code } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { code, strategy: 'email_code' },
         action: 'attempt_first_factor',
       });
@@ -807,19 +811,19 @@ class SignInFuture implements SignInFutureResource {
 
   async sendEmailLink(params: SignInFutureEmailLinkSendParams): Promise<{ error: ClerkError | null }> {
     const { emailAddress, verificationUrl, emailAddressId } = params;
-    if (!this.resource.id && emailAddressId) {
+    if (!this.#resource.id && emailAddressId) {
       throw new Error(
         'signIn.emailLink.sendLink() cannot be called with an emailAddressId if an existing signIn does not exist.',
       );
     }
 
-    if (!this.resource.id && !emailAddress) {
+    if (!this.#resource.id && !emailAddress) {
       throw new Error(
         'signIn.emailLink.sendLink() cannot be called without an emailAddress if an existing signIn does not exist.',
       );
     }
 
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       if (emailAddress) {
         await this._create({ identifier: emailAddress });
       }
@@ -836,7 +840,7 @@ class SignInFuture implements SignInFutureResource {
         absoluteVerificationUrl = window.location.origin + verificationUrl;
       }
 
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: {
           emailAddressId: emailLinkFactor.emailAddressId,
           redirectUrl: absoluteVerificationUrl,
@@ -848,12 +852,12 @@ class SignInFuture implements SignInFutureResource {
   }
 
   async waitForEmailLinkVerification(): Promise<{ error: ClerkError | null }> {
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       const { run, stop } = Poller();
       await new Promise((resolve, reject) => {
         void run(async () => {
           try {
-            const res = await this.resource.__internal_baseGet();
+            const res = await this.#resource.__internal_baseGet();
             const status = res.firstFactorVerification.status;
             if (status === 'verified' || status === 'expired') {
               stop();
@@ -870,19 +874,19 @@ class SignInFuture implements SignInFutureResource {
 
   async sendPhoneCode(params: SignInFuturePhoneCodeSendParams = {}): Promise<{ error: ClerkError | null }> {
     const { phoneNumber, phoneNumberId, channel = 'sms' } = params;
-    if (!this.resource.id && phoneNumberId) {
+    if (!this.#resource.id && phoneNumberId) {
       throw new Error(
         'signIn.phoneCode.sendCode() cannot be called with an phoneNumberId if an existing signIn does not exist.',
       );
     }
 
-    if (!this.resource.id && !phoneNumber) {
+    if (!this.#resource.id && !phoneNumber) {
       throw new Error(
         'signIn.phoneCode.sendCode() cannot be called without an phoneNumber if an existing signIn does not exist.',
       );
     }
 
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       if (phoneNumber) {
         await this._create({ identifier: phoneNumber });
       }
@@ -892,7 +896,7 @@ class SignInFuture implements SignInFutureResource {
         throw new ClerkRuntimeError('Phone code factor not found', { code: 'factor_not_found' });
       }
 
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { phoneNumberId: phoneCodeFactor.phoneNumberId, strategy: 'phone_code', channel },
         action: 'prepare_first_factor',
       });
@@ -901,8 +905,8 @@ class SignInFuture implements SignInFutureResource {
 
   async verifyPhoneCode(params: SignInFuturePhoneCodeVerifyParams): Promise<{ error: ClerkError | null }> {
     const { code } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { code, strategy: 'phone_code' },
         action: 'attempt_first_factor',
       });
@@ -912,7 +916,7 @@ class SignInFuture implements SignInFutureResource {
   async sso(params: SignInFutureSSOParams): Promise<{ error: ClerkError | null }> {
     const { strategy, redirectUrl, redirectCallbackUrl, popup, oidcPrompt, enterpriseConnectionId, identifier } =
       params;
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       let actionCompleteRedirectUrl = redirectUrl;
       try {
         new URL(redirectUrl);
@@ -937,7 +941,7 @@ class SignInFuture implements SignInFutureResource {
       });
 
       if (strategy === 'enterprise_sso') {
-        await this.resource.__internal_basePost({
+        await this.#resource.__internal_basePost({
           body: {
             ...routes,
             oidcPrompt,
@@ -948,13 +952,13 @@ class SignInFuture implements SignInFutureResource {
         });
       }
 
-      const { status, externalVerificationRedirectURL } = this.resource.firstFactorVerification;
+      const { status, externalVerificationRedirectURL } = this.#resource.firstFactorVerification;
 
       if (status === 'unverified' && externalVerificationRedirectURL) {
         if (popup) {
           await _futureAuthenticateWithPopup(SignIn.clerk, { popup, externalVerificationRedirectURL });
           // Pick up the modified SignIn resource
-          await this.resource.reload();
+          await this.#resource.reload();
         } else {
           windowNavigate(externalVerificationRedirectURL);
         }
@@ -966,7 +970,7 @@ class SignInFuture implements SignInFutureResource {
     const { strategy } = params;
     const provider = strategy.replace('web3_', '').replace('_signature', '') as Web3Provider;
 
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       let identifier;
       let generateSignature;
       switch (provider) {
@@ -992,14 +996,14 @@ class SignInFuture implements SignInFutureResource {
 
       await this._create({ identifier });
 
-      const web3FirstFactor = this.resource.supportedFirstFactors?.find(
+      const web3FirstFactor = this.#resource.supportedFirstFactors?.find(
         f => f.strategy === strategy,
       ) as Web3SignatureFactor;
       if (!web3FirstFactor) {
         throw new ClerkRuntimeError('Web3 first factor not found', { code: 'factor_not_found' });
       }
 
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { web3WalletId: web3FirstFactor.web3WalletId, strategy },
         action: 'prepare_first_factor',
       });
@@ -1026,7 +1030,7 @@ class SignInFuture implements SignInFutureResource {
         }
       }
 
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { signature, strategy },
         action: 'attempt_first_factor',
       });
@@ -1052,7 +1056,7 @@ class SignInFuture implements SignInFutureResource {
       });
     }
 
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       if (flow === 'autofill' || flow === 'discoverable') {
         await this._create({ strategy: 'passkey' });
       } else {
@@ -1061,7 +1065,7 @@ class SignInFuture implements SignInFutureResource {
         if (!passKeyFactor) {
           throw new ClerkRuntimeError('Passkey factor not found', { code: 'factor_not_found' });
         }
-        await this.resource.__internal_basePost({
+        await this.#resource.__internal_basePost({
           body: { strategy: 'passkey' },
           action: 'prepare_first_factor',
         });
@@ -1094,7 +1098,7 @@ class SignInFuture implements SignInFutureResource {
         throw new ClerkWebAuthnError(error.message, { code: 'passkey_retrieval_failed' });
       }
 
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: {
           publicKeyCredential: JSON.stringify(serializePublicKeyCredentialAssertion(publicKeyCredential)),
           strategy: 'passkey',
@@ -1105,15 +1109,15 @@ class SignInFuture implements SignInFutureResource {
   }
 
   async sendMFAPhoneCode(): Promise<{ error: ClerkError | null }> {
-    return runAsyncResourceTask(this.resource, async () => {
-      const phoneCodeFactor = this.resource.supportedSecondFactors?.find(f => f.strategy === 'phone_code');
+    return runAsyncResourceTask(this.#resource, async () => {
+      const phoneCodeFactor = this.#resource.supportedSecondFactors?.find(f => f.strategy === 'phone_code');
 
       if (!phoneCodeFactor) {
         throw new ClerkRuntimeError('Phone code factor not found', { code: 'factor_not_found' });
       }
 
       const { phoneNumberId } = phoneCodeFactor;
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { phoneNumberId, strategy: 'phone_code' },
         action: 'prepare_second_factor',
       });
@@ -1122,8 +1126,8 @@ class SignInFuture implements SignInFutureResource {
 
   async verifyMFAPhoneCode(params: SignInFutureMFAPhoneCodeVerifyParams): Promise<{ error: ClerkError | null }> {
     const { code } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { code, strategy: 'phone_code' },
         action: 'attempt_second_factor',
       });
@@ -1132,8 +1136,8 @@ class SignInFuture implements SignInFutureResource {
 
   async verifyTOTP(params: SignInFutureTOTPVerifyParams): Promise<{ error: ClerkError | null }> {
     const { code } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { code, strategy: 'totp' },
         action: 'attempt_second_factor',
       });
@@ -1142,8 +1146,8 @@ class SignInFuture implements SignInFutureResource {
 
   async verifyBackupCode(params: SignInFutureBackupCodeVerifyParams): Promise<{ error: ClerkError | null }> {
     const { code } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { code, strategy: 'backup_code' },
         action: 'attempt_second_factor',
       });
@@ -1158,15 +1162,15 @@ class SignInFuture implements SignInFutureResource {
   async finalize(params?: SignInFutureFinalizeParams): Promise<{ error: ClerkError | null }> {
     const { navigate } = params || {};
 
-    if (!this.resource.createdSessionId) {
+    if (!this.#resource.createdSessionId) {
       throw new Error('Cannot finalize sign-in without a created session.');
     }
 
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       // Reload the client to prevent an issue where the created session is not picked up.
       await SignIn.clerk.client?.reload();
 
-      await SignIn.clerk.setActive({ session: this.resource.createdSessionId, navigate });
+      await SignIn.clerk.setActive({ session: this.#resource.createdSessionId, navigate });
     });
   }
 
@@ -1184,12 +1188,12 @@ class SignInFuture implements SignInFutureResource {
     emailAddressId,
     phoneNumberId,
   }: SelectFirstFactorParams): EmailCodeFactor | EmailLinkFactor | PhoneCodeFactor | null {
-    if (!this.resource.supportedFirstFactors) {
+    if (!this.#resource.supportedFirstFactors) {
       return null;
     }
 
     if (emailAddressId) {
-      const factor = this.resource.supportedFirstFactors.find(
+      const factor = this.#resource.supportedFirstFactors.find(
         f => f.strategy === strategy && f.emailAddressId === emailAddressId,
       ) as EmailCodeFactor | EmailLinkFactor;
       if (factor) {
@@ -1198,7 +1202,7 @@ class SignInFuture implements SignInFutureResource {
     }
 
     if (phoneNumberId) {
-      const factor = this.resource.supportedFirstFactors.find(
+      const factor = this.#resource.supportedFirstFactors.find(
         f => f.strategy === strategy && f.phoneNumberId === phoneNumberId,
       ) as PhoneCodeFactor;
       if (factor) {
@@ -1207,15 +1211,15 @@ class SignInFuture implements SignInFutureResource {
     }
 
     // Try to find a factor that matches the identifier.
-    const factorForIdentifier = this.resource.supportedFirstFactors.find(
-      f => f.strategy === strategy && f.safeIdentifier === this.resource.identifier,
+    const factorForIdentifier = this.#resource.supportedFirstFactors.find(
+      f => f.strategy === strategy && f.safeIdentifier === this.#resource.identifier,
     ) as EmailCodeFactor | EmailLinkFactor | PhoneCodeFactor;
     if (factorForIdentifier) {
       return factorForIdentifier;
     }
 
     // If no factor is found matching the identifier, try to find a factor that matches the strategy.
-    const factorForStrategy = this.resource.supportedFirstFactors.find(f => f.strategy === strategy) as
+    const factorForStrategy = this.#resource.supportedFirstFactors.find(f => f.strategy === strategy) as
       | EmailCodeFactor
       | EmailLinkFactor
       | PhoneCodeFactor;
diff --git a/packages/clerk-js/src/core/resources/SignUp.ts b/packages/clerk-js/src/core/resources/SignUp.ts
index bb520ccdcea..f234ded2ddd 100644
--- a/packages/clerk-js/src/core/resources/SignUp.ts
+++ b/packages/clerk-js/src/core/resources/SignUp.ts
@@ -580,101 +580,105 @@ class SignUpFuture implements SignUpFutureResource {
     verifyPhoneCode: this.verifyPhoneCode.bind(this),
   };
 
-  constructor(readonly resource: SignUp) {}
+  readonly #resource: SignUp;
+
+  constructor(resource: SignUp) {
+    this.#resource = resource;
+  }
 
   get id() {
-    return this.resource.id;
+    return this.#resource.id;
   }
 
   get requiredFields() {
-    return this.resource.requiredFields;
+    return this.#resource.requiredFields;
   }
 
   get optionalFields() {
-    return this.resource.optionalFields;
+    return this.#resource.optionalFields;
   }
 
   get missingFields() {
-    return this.resource.missingFields;
+    return this.#resource.missingFields;
   }
 
   get status() {
     // @TODO hooks-revamp: Consolidate this fallback val with stateProxy
-    return this.resource.status || 'missing_requirements';
+    return this.#resource.status || 'missing_requirements';
   }
 
   get username() {
-    return this.resource.username;
+    return this.#resource.username;
   }
 
   get firstName() {
-    return this.resource.firstName;
+    return this.#resource.firstName;
   }
 
   get lastName() {
-    return this.resource.lastName;
+    return this.#resource.lastName;
   }
 
   get emailAddress() {
-    return this.resource.emailAddress;
+    return this.#resource.emailAddress;
   }
 
   get phoneNumber() {
-    return this.resource.phoneNumber;
+    return this.#resource.phoneNumber;
   }
 
   get web3Wallet() {
-    return this.resource.web3wallet;
+    return this.#resource.web3wallet;
   }
 
   get hasPassword() {
-    return this.resource.hasPassword;
+    return this.#resource.hasPassword;
   }
 
   get unsafeMetadata() {
-    return this.resource.unsafeMetadata;
+    return this.#resource.unsafeMetadata;
   }
 
   get createdSessionId() {
-    return this.resource.createdSessionId;
+    return this.#resource.createdSessionId;
   }
 
   get createdUserId() {
-    return this.resource.createdUserId;
+    return this.#resource.createdUserId;
   }
 
   get abandonAt() {
-    return this.resource.abandonAt;
+    return this.#resource.abandonAt;
   }
 
   get legalAcceptedAt() {
-    return this.resource.legalAcceptedAt;
+    return this.#resource.legalAcceptedAt;
   }
 
   get locale() {
-    return this.resource.locale;
+    return this.#resource.locale;
   }
 
   get unverifiedFields() {
-    return this.resource.unverifiedFields;
+    return this.#resource.unverifiedFields;
   }
 
   get isTransferable() {
     // TODO: we can likely remove the error code check as the status should be sufficient
     return (
-      this.resource.verifications.externalAccount.status === 'transferable' &&
-      this.resource.verifications.externalAccount.error?.code === 'external_account_exists'
+      this.#resource.verifications.externalAccount.status === 'transferable' &&
+      this.#resource.verifications.externalAccount.error?.code === 'external_account_exists'
     );
   }
 
   get existingSession() {
     if (
-      (this.resource.verifications.externalAccount.status === 'failed' ||
-        this.resource.verifications.externalAccount.status === 'unverified') &&
-      this.resource.verifications.externalAccount.error?.code === 'identifier_already_signed_in' &&
-      this.resource.verifications.externalAccount.error?.meta?.sessionId
+      (this.#resource.verifications.externalAccount.status === 'failed' ||
+        this.#resource.verifications.externalAccount.status === 'unverified') &&
+      this.#resource.verifications.externalAccount.error?.code === 'identifier_already_signed_in' &&
+      this.#resource.verifications.externalAccount.error?.meta?.sessionId
     ) {
-      return { sessionId: this.resource.verifications.externalAccount.error?.meta?.sessionId };
+      return { sessionId: this.#resource.verifications.externalAccount.error?.meta?.sessionId };
     }
 
     return undefined;
@@ -708,28 +712,28 @@ class SignUpFuture implements SignUpFutureResource {
       locale: params.locale ?? getBrowserLocale(),
     };
 
-    await this.resource.__internal_basePost({ path: this.resource.pathRoot, body });
+    await this.#resource.__internal_basePost({ path: this.#resource.pathRoot, body });
   }
 
   async create(params: SignUpFutureCreateParams): Promise<{ error: ClerkError | null }> {
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       await this._create(params);
     });
   }
 
   async update(params: SignUpFutureUpdateParams): Promise<{ error: ClerkError | null }> {
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       const body: Record<string, unknown> = {
         ...params,
         unsafeMetadata: params.unsafeMetadata ? normalizeUnsafeMetadata(params.unsafeMetadata) : undefined,
       };
 
-      await this.resource.__internal_basePatch({ path: this.resource.pathRoot, body });
+      await this.#resource.__internal_basePatch({ path: this.#resource.pathRoot, body });
     });
   }
 
   async password(params: SignUpFuturePasswordParams): Promise<{ error: ClerkError | null }> {
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       const { captchaToken, captchaWidgetType, captchaError } = await this.getCaptchaToken();
 
       const body: Record<string, unknown> = {
@@ -741,13 +745,13 @@ class SignUpFuture implements SignUpFutureResource {
         unsafeMetadata: params.unsafeMetadata ? normalizeUnsafeMetadata(params.unsafeMetadata) : undefined,
       };
 
-      await this.resource.__internal_basePost({ path: this.resource.pathRoot, body });
+      await this.#resource.__internal_basePost({ path: this.#resource.pathRoot, body });
     });
   }
 
   async sendEmailCode(): Promise<{ error: ClerkError | null }> {
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { strategy: 'email_code' },
         action: 'prepare_verification',
       });
@@ -756,8 +760,8 @@ class SignUpFuture implements SignUpFutureResource {
 
   async verifyEmailCode(params: SignUpFutureEmailCodeVerifyParams): Promise<{ error: ClerkError | null }> {
     const { code } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { strategy: 'email_code', code },
         action: 'attempt_verification',
       });
@@ -766,16 +770,16 @@ class SignUpFuture implements SignUpFutureResource {
 
   async sendPhoneCode(params: SignUpFuturePhoneCodeSendParams): Promise<{ error: ClerkError | null }> {
     const { phoneNumber, channel = 'sms' } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      if (!this.resource.id) {
+    return runAsyncResourceTask(this.#resource, async () => {
+      if (!this.#resource.id) {
         const { captchaToken, captchaWidgetType, captchaError } = await this.getCaptchaToken();
-        await this.resource.__internal_basePost({
-          path: this.resource.pathRoot,
+        await this.#resource.__internal_basePost({
+          path: this.#resource.pathRoot,
           body: { phoneNumber, captchaToken, captchaWidgetType, captchaError },
         });
       }
 
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { strategy: 'phone_code', channel },
         action: 'prepare_verification',
       });
@@ -784,8 +788,8 @@ class SignUpFuture implements SignUpFutureResource {
 
   async verifyPhoneCode(params: SignUpFuturePhoneCodeVerifyParams): Promise<{ error: ClerkError | null }> {
     const { code } = params;
-    return runAsyncResourceTask(this.resource, async () => {
-      await this.resource.__internal_basePost({
+    return runAsyncResourceTask(this.#resource, async () => {
+      await this.#resource.__internal_basePost({
         body: { strategy: 'phone_code', code },
         action: 'attempt_verification',
       });
@@ -804,7 +808,7 @@ class SignUpFuture implements SignUpFutureResource {
       emailAddress,
       popup,
     } = params;
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       const { captchaToken, captchaWidgetType, captchaError } = await this.getCaptchaToken();
 
       let redirectUrlComplete = redirectUrl;
@@ -828,8 +832,8 @@ class SignUpFuture implements SignUpFutureResource {
       }
 
       const authenticateFn = () => {
-        return this.resource.__internal_basePost({
-          path: this.resource.pathRoot,
+        return this.#resource.__internal_basePost({
+          path: this.#resource.pathRoot,
           body: {
             strategy,
             ...routes,
@@ -854,13 +858,13 @@ class SignUpFuture implements SignUpFutureResource {
         throw e;
       });
 
-      const { status, externalVerificationRedirectURL } = this.resource.verifications.externalAccount;
+      const { status, externalVerificationRedirectURL } = this.#resource.verifications.externalAccount;
 
       if (status === 'unverified' && externalVerificationRedirectURL) {
         if (popup) {
           await _futureAuthenticateWithPopup(SignUp.clerk, { popup, externalVerificationRedirectURL });
           // Pick up the modified SignUp resource
-          await this.resource.reload();
+          await this.#resource.reload();
         } else {
           windowNavigate(externalVerificationRedirectURL);
         }
@@ -872,7 +876,7 @@ class SignUpFuture implements SignUpFutureResource {
     const { strategy, unsafeMetadata, legalAccepted } = params;
     const provider = strategy.replace('web3_', '').replace('_signature', '') as Web3Provider;
 
-    return runAsyncResourceTask(this.resource, async () => {
+    return runAsyncResourceTask(this.#resource, async () => {
       let identifier;
       let generateSignature;
       switch (provider) {
@@ -897,14 +901,14 @@ class SignUpFuture implements SignUpFutureResource {
       }
 
       // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-      const web3Wallet = identifier || this.resource.web3wallet!;
+      const web3Wallet = identifier || this.#resource.web3wallet!;
       await this._create({ web3Wallet, unsafeMetadata, legalAccepted });
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { strategy },
         action: 'prepare_verification',
       });
 
-      const { message } = this.resource.verifications.web3Wallet;
+      const { message } = this.#resource.verifications.web3Wallet;
       if (!message) {
         clerkVerifyWeb3WalletCalledBeforeCreate('SignUp');
       }
@@ -927,7 +931,7 @@ class SignUpFuture implements SignUpFutureResource {
         }
       }
 
-      await this.resource.__internal_basePost({
+      await this.#resource.__internal_basePost({
         body: { signature, strategy },
         action: 'attempt_verification',
       });
@@ -941,12 +945,12 @@ class SignUpFuture implements SignUpFutureResource {
 
   async finalize(params?: SignUpFutureFinalizeParams): Promise<{ error: ClerkError | null }> {
     const { navigate } = params || {};
-    return runAsyncResourceTask(this.resource, async () => {
-      if (!this.resource.createdSessionId) {
+    return runAsyncResourceTask(this.#resource, async () => {
+      if (!this.#resource.createdSessionId) {
         throw new Error('Cannot finalize sign-up without a created session.');
       }
 
-      await SignUp.clerk.setActive({ session: this.resource.createdSessionId, navigate });
+      await SignUp.clerk.setActive({ session: this.#resource.createdSessionId, navigate });
     });
   }
 }
diff --git a/packages/clerk-js/src/core/resources/__tests__/SignIn.test.ts b/packages/clerk-js/src/core/resources/__tests__/SignIn.test.ts
index d168a79d57d..8460a87ce49 100644
--- a/packages/clerk-js/src/core/resources/__tests__/SignIn.test.ts
+++ b/packages/clerk-js/src/core/resources/__tests__/SignIn.test.ts
@@ -16,6 +16,12 @@ vi.mock('../../../utils/authenticateWithPopup', async () => {
 import { _futureAuthenticateWithPopup } from '../../../utils/authenticateWithPopup';
 
 describe('SignIn', () => {
+  it('can be serialized with JSON.stringify', () => {
+    const signIn = new SignIn();
+    const snapshot = JSON.stringify(signIn);
+    expect(snapshot).toBeDefined();
+  });
+
   describe('signIn.create', () => {
     afterEach(() => {
       vi.clearAllMocks();
@@ -71,6 +77,12 @@ describe('SignIn', () => {
   });
 
   describe('SignInFuture', () => {
+    it('can be serialized with JSON.stringify', () => {
+      const signIn = new SignIn();
+      const snapshot = JSON.stringify(signIn.__internal_future);
+      expect(snapshot).toBeDefined();
+    });
+
     describe('selectFirstFactor', () => {
       beforeAll(() => {
         const signInCreatedJSON = {
diff --git a/packages/clerk-js/src/core/resources/__tests__/SignUp.test.ts b/packages/clerk-js/src/core/resources/__tests__/SignUp.test.ts
index a0f6dbf653b..d6771c120c4 100644
--- a/packages/clerk-js/src/core/resources/__tests__/SignUp.test.ts
+++ b/packages/clerk-js/src/core/resources/__tests__/SignUp.test.ts
@@ -26,7 +26,19 @@ vi.mock('../../../utils/captcha/CaptchaChallenge', () => ({
 }));
 
 describe('SignUp', () => {
+  it('can be serialized with JSON.stringify', () => {
+    const signUp = new SignUp();
+    const snapshot = JSON.stringify(signUp);
+    expect(snapshot).toBeDefined();
+  });
+
   describe('SignUpFuture', () => {
+    it('can be serialized with JSON.stringify', () => {
+      const signUp = new SignUp();
+      const snapshot = JSON.stringify(signUp.__internal_future);
+      expect(snapshot).toBeDefined();
+    });
+
     describe('create', () => {
       afterEach(() => {
         vi.clearAllMocks();