This study reports the observation of the chiral anomaly in multifold fermions within CoSi, a chiral crystal hosting multifold bands around the Fermi level. The chiral anomaly, a phenomenon associated with chiral spin-1/2 Weyl fermions, leads to an imbalance between left- and right-moving particles, resulting in negative longitudinal magnetoresistance in Weyl semimetals. The research demonstrates that this effect is also present in multifold fermions, despite their larger orbital magnetic moment, which previously was thought to suppress the chiral anomaly. The study uses a semiclassical theory of magnetotransport for multifold fermions, showing that the negative magnetoresistance arises from the chiral anomaly. The results are supported by experimental measurements of magnetotransport in CoSi, including a negative longitudinal magnetoresistance and a nonlinear Hall effect. The study confirms the chiral anomaly of higher-spin generalizations of Weyl fermions, which are not accessible in high-energy physics. The findings highlight the importance of multifold fermions in understanding quantum anomalies and their role in novel electronic properties. The research also addresses the challenge of identifying chiral semimetals with multifold fermions within a large energy window around the Fermi level, and confirms that CoSi is a suitable material for such studies. The study provides a comprehensive understanding of the chiral anomaly in multifold fermions and its implications for quantum materials.This study reports the observation of the chiral anomaly in multifold fermions within CoSi, a chiral crystal hosting multifold bands around the Fermi level. The chiral anomaly, a phenomenon associated with chiral spin-1/2 Weyl fermions, leads to an imbalance between left- and right-moving particles, resulting in negative longitudinal magnetoresistance in Weyl semimetals. The research demonstrates that this effect is also present in multifold fermions, despite their larger orbital magnetic moment, which previously was thought to suppress the chiral anomaly. The study uses a semiclassical theory of magnetotransport for multifold fermions, showing that the negative magnetoresistance arises from the chiral anomaly. The results are supported by experimental measurements of magnetotransport in CoSi, including a negative longitudinal magnetoresistance and a nonlinear Hall effect. The study confirms the chiral anomaly of higher-spin generalizations of Weyl fermions, which are not accessible in high-energy physics. The findings highlight the importance of multifold fermions in understanding quantum anomalies and their role in novel electronic properties. The research also addresses the challenge of identifying chiral semimetals with multifold fermions within a large energy window around the Fermi level, and confirms that CoSi is a suitable material for such studies. The study provides a comprehensive understanding of the chiral anomaly in multifold fermions and its implications for quantum materials.