What is current

Last reviewed 2026-08-09.

The current formulation of IIT is IIT 4.0, as set out in Albantakis et al. (2023), with system integrated information (φ_s) defined as in Mayner, Marshall & Tononi (2026), which adds the intrinsic-information requirement.

For an account without the mathematics, read Tononi & Boly (2025), "Integrated Information Theory: A Consciousness-First Approach to What Exists".

PyPhi 2.0 computes these quantities.

Earlier formulations

Earlier formulations of the theory include IIT 3.0 (Oizumi, Albantakis & Tononi 2014) and IIT 2.0.