In recent years; the operation and planning of electrical power systems has undergone a paradigm shift; driven by technological evolution; the energy transition and the growing participation of new agents in the electricity system. In the Colombian context; the need for modernization and the implementation of flexibility criteria in planning are essential to face these challenges and guarantee a safe; reliable; quality and economical operation. The current methodological framework of the UPME for the definition of electrical infrastructure requires a significant transformation to adapt to these new dynamics and conditions. The increase in self-generators; distributed generators; energy communities; regulable demand; and the growing penetration of non-conventional renewable energy sources (FNCER) have introduced an unprecedented level of uncertainty and variability into the electricity system. This variability hinders accurate forecasting of supply and demand; as well as the ability to effectively plan the development of electrical infrastructure. Traditional planning; based on deterministic and rigid methodologies; is no longer sufficient to address these challenges. Instead; it is necessary to incorporate flexibility criteria that allow greater adaptability to the volatility of the system. Flexibility in planning becomes essential to effectively manage changes and ensure optimal system operation. It is imperative that planning methodologies be updated to be more accurate and expeditious; considering the speed with which power systems evolve. This approach will ensure that the expansion and development of the electricity system responds to the country's needs in real time; without compromising the reliability and security of the system. There is a growing need for a coordinated charge control and generation strategy through digitalization and automation. At the same time; power systems around the world have been integrating smart grid technologies into the planning of transmission systems. In addition; the current context of expansion of the electricity system faces growing barriers; particularly in the construction of new transmission lines and substations. Therefore; it is essential to optimize the existing infrastructure by implementing advanced technologies; such as energy storage systems; HVDC systems; synchronous compensators; DLRs; SSSCs and high-temperature conductors. These solutions not only maximize the use of the infrastructure already in place; but also provide the flexibility needed to operate a more complex and dynamic system. In summary; the modernization and implementation of flexibility criteria in the planning of the Colombian electricity system are crucial to face the challenges of the energy transition. The definition of new robust and flexible methodologies will not only guarantee the safe; reliable and economical operation of the system; but also optimize the use of existing infrastructure and facilitate the integration of new technologies and agents in the electricity system.