diff --git a/docs/PI.md b/docs/PI.md
index 9610ced..674cae5 100644
--- a/docs/PI.md
+++ b/docs/PI.md
@@ -73,7 +73,32 @@ Current v1 decision:
 - document the extension opportunities explicitly
 - only add an extension later if it removes meaningful friction that documentation and helper scripts cannot address cleanly
 
-This section is intentionally provisional until M4, which records the final v1 extension assessment in this document.
+See [Extension Assessment](#extension-assessment) for the final v1 decision.
+
+## Extension Assessment
+
+The upstream pi extension docs make three candidate areas realistic for this repo:
+
+| Candidate | What It Could Add | V1 Decision | Rationale |
+|-----------|-------------------|-------------|-----------|
+| Todo tracking extension | A pi-native task list or command for story state transitions while running `create-plan`, `do-task`, or `implement-plan` | Defer | The current file-backed trackers already work across agents, so shipping an extension now would add maintenance cost without unlocking base usability. |
+| Reviewer-loop extension | A pi-native wrapper around the reviewer-runtime flow, potentially exposing review runs as a command or tool instead of shell glue | Defer | The standalone `run-review.sh` helper is enough for v1, and deferring keeps the package surface smaller while usage patterns are still unknown. |
+| Sub-agent orchestration extension | Higher-level automation for worktree setup, milestone stepping, or multi-run coordination | Defer | This is the highest-complexity option and most likely to overfit early assumptions before the pi variants have real usage feedback. |
+
+### Final V1 Decision
+
+All extension candidates are deferred for v1.
+
+The v1 package should ship:
+
+- pi skill variants
+- shared pi docs
+- pi reviewer-runtime helper scripts
+- verification tooling
+
+It should not require any pi extension to be usable.
+
+The threshold for a follow-up extension should be concrete, repeated friction that cannot be addressed cleanly with documentation, templates, or helper scripts alone.
 
 ## Scope Notes