In a HCP Terraform/Terraform Cloud workspace linked to a version control repository, speculative plan runs start automatically when you merge or commit changes to version control.
Speculative Plans: Terraform Cloud'sspeculative planfeature runs automatically when changes are detected in a linked VCS repository, enabling users to review potential infrastructure changes without committing them.
Automatic Integration: This feature automates the planning process by triggering when changes are committed, aiding teams in previewing infrastructure changes seamlessly.
For further understanding, see theTerraform Cloud VCS Integrationdocumentation.