This Act, known as the HALT Fentanyl Act , amends the Controlled Substances Act to permanently place fentanyl-related substances into Schedule I, ensuring they are subject to strict federal controls. This classification covers any material, compound, mixture, or preparation containing such substances, or their salts and isomers, unless already controlled or listed elsewhere. The Act defines these substances by specific structural modifications to fentanyl, authorizing the Attorney General to publish lists, though absence from a list does not negate their controlled status. A key provision introduces expedited registration procedures for practitioners conducting certain research with Schedule I substances, specifically those under an FDA investigational use exemption or funded by federal health and defense agencies. Researchers already registered for Schedule I or II substances can begin qualifying research with a 30-day notice to the Attorney General, while new researchers receive a 45-day processing timeline for their applications. The Act also mandates electronic submission options and limits researchers to possessing only the amounts identified in their notifications. The Act streamlines research further by allowing agents within a registered institution to conduct research without separate registration, and permits a single registration for multiple research sites within the same city or county under one institution. It also clarifies that new inspections are not required when adding a controlled substance in the same or a higher numerical schedule for research. Researchers can continue studies on substances newly added to Schedule I while their registration modification is pending, and small-quantity manufacturing for research purposes is permitted without a separate manufacturing registration. To ensure transparency, the Attorney General must make public any special processes or criteria for Schedule I research applications. The Act explicitly includes fentanyl-related substances in the penalty provisions for drug trafficking and importation, and requires the Attorney General to issue interim final rules within six months. These amendments apply from the date of enactment, clarifying that this Act does not imply fentanyl-related substances were not analogues prior to its passage.