MLPs in this work were trained using ACE.jl v0.8.4 wrapped with pyjulip via mlp-train package. MLPs for reactions R1 and R2 were trained with the energy selector with energy threshold of 0.1 eV, while the similarity selector with similarity threshold of 0.9995 using SOAP descriptor was applied for the reaction R3. MLPs were evaluated using Atomic Simulation Environment (ASE) v3.23.0b1 and WTMetaD bias was calculated using the PLUMED plugin integrated with ASE. Hyperparameters of ACE, selectors and WTMetaD bias, used in training ACE MLPs are listed in Table . The MD-MLP simulations in AL were performed at a constant temperature of 500 K in the case of Downhill AL and 300 K for WTMetaD-IB AL. Constant temperature MD was performed using Langevin dynamics with a friction coefficient of 0.02 in inverse ASE time units (Å u/eV where u is the atomic mass unit) and a timestep of 0.5 fs. Velocities were initialised using Maxwell-Boltzmann distribution at the corresponding temperatures (Downhill AL at 500 K and WTMetaD AL at 300 K). More details on hyperparameters of MLPs and WTMetaD in AL are provided in SI §S1. Electronic structure calculations were performed using ORCA 5.0.3 wrapped with autodE 79 via mlp-train package. The PBE0-D3BJ/def2-SVP method with Conductorlike Polarizable Continuum Model (CPCM) for water was selected as the ground-truth method for reaction R1. The IRC for the reaction R1 was obtained by directly using ORCA 5.0.3 at the same level of theory. The independent testing set was generated by US/AIMD for the reaction R1 with a reaction coordinate of r Cl -r F , where r Cl is the bond length between C and Cl atoms and r F is the bond length between C and F atoms, with 16 windows, which were equally spaced in [-0.73, 1.85] Å with the force constant k = 15 eV Å -2 , for 200 fs per window at 300 K in the NVT ensemble at the ground-truth level of theory. The PBE0-D3BJ/def2-SVP was used as the ground-truth method for R2. The US/AIMD ran along r 1 -r 2 with 30 windows, which were equally spaced in [-0.97, 1.03] Å with k = 20 eV Å -2 , for 100 fs per window at 300 K at the same level of theory. The PBE-D3BJ/def2-TZVP method was used to label energies and forces for reaction R3.