43 CFR §2.21

1. (a)When the bureau informs you of its decision to comply with a request by granting, partially granting, or denying the request, it will do so in writing and in accordance with the deadlines in subpart D of this part. The bureau's written response will include a statement about the services offered by the FOIA Public Liaison. The bureau's written response will also include a statement about the services offered by OGIS, using standard language that can be found at: https://www.doi.gov/foia/news/guidance.”
2. (b)If the bureau determines that your request will take longer than 10 workdays to process, the bureau immediately will send you a written acknowledgment that includes the request's individualized tracking number and processing track (see § 2.15(e)). The acknowledgement may also include a brief description of the subject of your request.