The Halt All Lethal Trafficking of Fentanyl Act, or HALT Fentanyl Act, primarily amends the Controlled Substances Act (CSA) to permanently place all fentanyl-related substances into Schedule I. This means any material, compound, mixture, or preparation containing a fentanyl-related substance, as defined by specific structural modifications to fentanyl, will be subject to the most stringent controls. Exceptions apply if a substance is already controlled by the Attorney General or listed in another schedule, and the Attorney General is authorized to publish lists of these substances. A significant portion of the bill focuses on streamlining the registration process for practitioners conducting research with Schedule I controlled substances. It establishes an expedited procedure for research involving drugs under an investigational use exemption from the FDA, or research conducted or funded by the Department of Health and Human Services, Department of Defense, or Department of Veterans Affairs. Researchers with existing Schedule I or II registrations can begin research 30 days after notifying the Attorney General, while new applicants will have their notice treated as an application for expedited review. Further provisions aim to reduce administrative burdens on researchers. An agent or employee of a registered research institution may conduct research without a separate registration if certain conditions are met, including authorization and affirmation by the registered researcher. Additionally, a single registration can cover research conducted at multiple sites within the same city or county under the control of the same institution. The bill also clarifies that new inspections are not required for certain modifications to existing research registrations and allows for the continuation of research on substances newly added to Schedule I. The Act permits small-scale manufacturing activities coincident with research, such as creating extracts or developing dosage forms, without requiring a separate manufacturing registration, though this authority does not extend to growing marijuana. To ensure transparency, the Attorney General must publicly disclose any special processes or criteria applied to research applications for specific controlled substances. Finally, the bill amends penalty provisions for trafficking and importation to explicitly include fentanyl-related substances, and mandates the Attorney General to issue interim final rules within six months to implement these changes, which will apply from the date of enactment.