diff --git a/AGENTS.md b/AGENTS.md
index 00bb4dc..3e87f4d 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -153,6 +153,9 @@ graphify update .               # refresh after code changes (AST-only, no API c
   Slow, GPU, Simpleware,
   experiment, and tutorial tests are auto-skipped unless their opt-in flag is
   passed.
+- Do not run pytest with `--run-slow` or `--run-all` unless the user explicitly
+  asks; those runs take far too long for an interactive session. Default to the
+  fast suite and leave the opt-in buckets for the user to invoke.
 - Query the graphify knowledge graph (`graphify query "<question>"`) to locate
   classes, methods, and signatures before searching manually.
 - Do not commit changes or make pull requests unless specifically told to do so.
diff --git a/CLAUDE.md b/CLAUDE.md
index 990efcd..177bf2d 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -136,6 +136,9 @@ came from.
 - Markers (all opt-in via `--run-<bucket>`): `slow`, `requires_gpu`,
   `requires_simpleware`, `experiment`, `tutorial`. Data-dependent tests no
   longer use a marker — they pull data through fixtures and run by default.
+- **Avoid `pytest --run-slow` (or `--run-all`) unless the user explicitly
+  requests it.** Those runs take far too long for an interactive session.
+  Default to the fast suite and let the user invoke the slow buckets.
 - Prefer images from `ROOT/data/test/slicer_heart_small` for tests
 - Prefer storing results in subdirs `./results/<test_name>`