Migration for existing users
When you upgrade to a version of Hermes that has opt-in plugins (config schema v21+), any user plugins already installed under ~/.hermes/plugins/ that weren't already in plugins.disabled are automatically grandfathered into plugins.enabled . Your existing setup keeps working. Bundled standalone plugins are NOT grandfathered - even existing users have to opt in explicitly. (Bundled platform/backend plugins never needed grandfathering because they were never gated.)
From the official Hermes Agent documentation.