I would occasionally, back in the day, require extremely fast film. I encountered a recommendation for processing TRI-X exposed at EI 4000, tried it, and found that it produced very useful results. (Contrast was high, shadow-detail was low, but grain was startling small, and if properly exposed it lead to a very satisfying rendition of the scene for late-night convention parties and music sessions. The film had a strong curl, and a high level of base fog.)
I just ran across a pointer to the details of the process, which I hadn’t quite remembered, and a citation to where it originally from. I don’t expect to ever use it again (though the materials are still available!), but I’ve been unhappy not remembering the details, so I’m documenting them here, as well as where a re-discovered them.
Michael G. Slack (in Darkroom Photography, July/August 1979, p. 13) reports pushing Kodak Tri-X Pan to EI 4000 (with extreme contrast increase) by developing for 5 minutes at 75 F in HC-110 replenisher diluted 1:15 (like Dilution A, but starting with replenisher rather than syrup).
Michael Covington, https://www.covingtoninnovations.com/hc110/