All, I tried Alfredo's suggestion of building with the stage1 compiler. (Sticking with the bootstrap compiler for HLS support, which seems to be working OK.) I've gotten a bit further. I have a small app that loads .hs files, translates to STG, and dumps the results. It also dumps the `ModSummary` for each module in the graph. The code worked in the 9.0 API, but using the 9.3 API causes a panic: nr@homedog ~/a/sandbox> cabal v1-build Resolving dependencies... Configuring sandbox-0.1.0.0... Preprocessing executable 'sandbox' for sandbox-0.1.0.0.. Building executable 'sandbox' for sandbox-0.1.0.0.. [1 of 1] Compiling Main ( app/Main.hs, dist/build/sandbox/sandbox-tmp/Main.o ) [Source file changed] Linking dist/build/sandbox/sandbox ... nr@homedog ~/a/sandbox> ./dist/build/sandbox/sandbox programs/Church.hs libdir == /home/nr/asterius/ghc/_build/stage1/lib ModSummary { ms_hs_hash = 8ed607a72dd3968f1e65123b865b8572 ms_mod = Church, ms_textual_imps = [(Nothing, Prelude)] ms_srcimps = [] } .............. sandbox: panic! (the 'impossible' happened) GHC version 9.3.20210918: unsafeGetHomeUnit: No home unit Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug I poked around, but I expected the home unit to be set by `setSessionDynFlags`, and I don't know why it isn't. Everything needed to reproduce the problem can be found (I hope!) at https://github.com/nrnrnr/ghc-api-sandbox I'm a bit reluctant to simply report a bug as I'm afraid I might be doing something wacky. What should I look at next? Norman