> ## Documentation Index
> Fetch the complete documentation index at: https://www.plain.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# upsertThreadField

> Sets (or updates) a single thread field value on a thread, identified by thread ID and field key. Creates the field if it does not exist, or overwrites the existing value if it does. Requires the `threadField:create` and `threadField:update` permissions.