# PlanSys2 4.0.0 brings PDDL+ support and hardened ROS 2 planning framework

> **Key takeaway:** PlanSys2 4.0.0 is a single release for four ROS 2 distributions that adds PDDL+ coverage and hardened reliability against process failures, network issues, and hostile inputs.

**Published:** 2026-10-21T18:14:15+00:00 
**Source:** ROS Robot Operating System News 
**Category:** robotics-science 
**Canonical URL:** https://fosswire.org/news/plansys2-400-brings-pddl-support-and-hardened-ros-2-planning.html 

## Summary
PlanSys2 4.0.0 has been released as a unified version for ROS 2 Humble, Jazzy, Kilted, and Lyrical. The framework, used in logistics robots and NASA's Astrobee, now covers PDDL from version 1.2 through PDDL+ including durative actions, numeric fluents, and timed processes. Kairos is now the default planner, and a new STN behavior tree builder preserves concurrency and time constraints during execution. The release was validated with sanitizers, fuzzing, and stress testing across three DDS implementations.

## What's new in PlanSys2 4.0.0
- **PDDL coverage expanded**: Supports PDDL 1.2 through PDDL+, including STRIPS, typing, conditional effects, derived predicates, numeric fluents, durative actions, timed initial literals, PDDL3 preferences/constraints, object fluents, and PDDL+ processes/events
- **New default planner**: Kairos replaces previous planner; claimed to cover more of PDDL than any other planner with faster performance
- **STN behavior tree builder**: Now default; executes plans while preserving action concurrency and time constraints
- **Hardened reliability**: Handles arbitrary start order, process death/recovery with state restoration, lost messages, network delays, loaded systems, API misuse, and hostile inputs
- **Validation**: Tested with sanitizers, fuzzing, and stress bench across Fast DDS, Cyclone DDS, and Zenoh
- **Single release for four ROS 2 distributions**: Humble, Jazzy, Kilted, and Lyrical

## Why it matters
PlanSys2 has become a baseline for task planning with LLMs in robotics, and this release's unified versioning across four ROS 2 distributions reduces maintenance fragmentation for researchers and companies deploying logistics or space robotics.