Yes, you can install Windows 10 without a product key, but there are some limitations to be aware of.

When you first install Windows 10, you can choose to bypass the product key entering during the setup process. This enables you to complete the installation without immediately launching Windows. However, there are repercussions for not activating your copy of Windows.

1. Limited functionality: Unactivated Windows 10 operates in a reduced functionality mode. You may encounter restrictions on personalization settings, and a watermark will be displayed on the desktop reminding you to activate Windows.
2. No Microsoft support: Without activation, you won't be eligible for Microsoft support, and you won't receive updates, which include security updates.
3. Activation prompts: Windows will regularly prompt you to activate, and the reminders can be persistent.

If you intend to use Windows 10 for an extended period of time and want to have full access to all features, you should obtain a valid product key and activate your copy. Product keys are available for purchase from Microsoft or approved retailers.

If you have a device with Windows 10 pre-installed, you may also use the Windows 10 activation troubleshooter to link your digital license to your Microsoft account.

While Windows 10 may be installed without a product key, activating your copy allows you to take advantage of all of its features and benefits, including continuing support and updates.