diff --git a/next/genesis/activity-types/delete.sx b/next/genesis/activity-types/delete.sx
new file mode 100644
index 00000000..22c04c70
--- /dev/null
+++ b/next/genesis/activity-types/delete.sx
@@ -0,0 +1,13 @@
+;; next/genesis/activity-types/delete.sx
+;;
+;; Bootstrap definition of the Delete verb per design §3 and §12.2.
+;; Read as data by the bundler — never evaluated as code here. The
+;; :schema and :semantics bodies are SX source; the validator
+;; pipeline (Step 6) and projection scheduler (Step 7) evaluate them
+;; at the appropriate times.
+
+(DefineActivity
+  :name "Delete"
+  :doc "Tombstone an existing object. :object is the CID of the\n        target. Projections fold Delete by removing the object from\n        their working indexes; the underlying log line is never\n        erased — durability of the historical record is independent\n        of projection state."
+  :schema (fn (act) (string? (-> act :object)))
+  :semantics (fn (state act) state))
diff --git a/next/genesis/activity-types/update.sx b/next/genesis/activity-types/update.sx
new file mode 100644
index 00000000..90e2c77d
--- /dev/null
+++ b/next/genesis/activity-types/update.sx
@@ -0,0 +1,15 @@
+;; next/genesis/activity-types/update.sx
+;;
+;; Bootstrap definition of the Update verb per design §3 and §12.2.
+;; Read as data by the bundler — never evaluated as code here. The
+;; :schema and :semantics bodies are SX source; the validator
+;; pipeline (Step 6) and projection scheduler (Step 7) evaluate them
+;; at the appropriate times.
+
+(DefineActivity
+  :name "Update"
+  :doc "Patch or replace an existing object. :object is the CID of\n        the target; :patch is the field-level edit. Behaviour is\n        delegated to per-object-type semantics — e.g. an Update of a\n        DefineActivity supersedes the prior registry entry; an\n        Update of a Person actor rotates keys via :patch :add-publicKey\n        + :patch :supersede."
+  :schema (fn
+    (act)
+    (and (string? (-> act :object)) (not (nil? (-> act :patch)))))
+  :semantics (fn (state act) state))
diff --git a/next/genesis/manifest.sx b/next/genesis/manifest.sx
index bd62daa3..607197f2 100644
--- a/next/genesis/manifest.sx
+++ b/next/genesis/manifest.sx
@@ -18,7 +18,9 @@
 (GenesisManifest
   :version "0.0.1"
   :kernel-version "1.0.0-m1"
-  :activity-types ("activity-types/create.sx")
+  :activity-types ("activity-types/create.sx"
+    "activity-types/update.sx"
+    "activity-types/delete.sx")
   :object-types ()
   :projections ()
   :validators ()
diff --git a/next/tests/genesis_parse.sh b/next/tests/genesis_parse.sh
index d10f1ac6..eb1fc5d7 100755
--- a/next/tests/genesis_parse.sh
+++ b/next/tests/genesis_parse.sh
@@ -3,7 +3,7 @@
 #
 # Confirms the seed genesis SX files parse cleanly and have the
 # expected top-level head form. The bundler (Step 4c+) consumes
-# these forms directly as data. 5 cases.
+# these forms directly as data. 10 cases.
 
 set -uo pipefail
 cd "$(git rev-parse --show-toplevel)"
@@ -32,6 +32,16 @@ cat > "$TMPFILE" <<'EPOCHS'
 (eval "(get (apply dict (rest (parse (file-read \"next/genesis/activity-types/create.sx\")))) :name)")
 (epoch 14)
 (eval "(get (apply dict (rest (parse (file-read \"next/genesis/manifest.sx\")))) :version)")
+(epoch 15)
+(eval "(first (parse (file-read \"next/genesis/activity-types/update.sx\")))")
+(epoch 16)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/activity-types/update.sx\")))) :name)")
+(epoch 17)
+(eval "(first (parse (file-read \"next/genesis/activity-types/delete.sx\")))")
+(epoch 18)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/activity-types/delete.sx\")))) :name)")
+(epoch 19)
+(eval "(len (get (apply dict (rest (parse (file-read \"next/genesis/manifest.sx\")))) :activity-types))")
 EPOCHS
 
 OUTPUT=$(timeout 30 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -60,6 +70,11 @@ check 11 "create.sx head form"          "DefineActivity"
 check 12 "manifest lists create.sx"     "activity-types/create.sx"
 check 13 "create.sx name is Create"     "Create"
 check 14 "manifest version present"     "0.0.1"
+check 15 "update.sx head form"          "DefineActivity"
+check 16 "update.sx name is Update"     "Update"
+check 17 "delete.sx head form"          "DefineActivity"
+check 18 "delete.sx name is Delete"     "Delete"
+check 19 "manifest has 3 activity-types" "3"
 
 TOTAL=$((PASS+FAIL))
 if [ $FAIL -eq 0 ]; then
diff --git a/plans/fed-sx-milestone-1.md b/plans/fed-sx-milestone-1.md
index 1a00e992..5c0eca16 100644
--- a/plans/fed-sx-milestone-1.md
+++ b/plans/fed-sx-milestone-1.md
@@ -245,7 +245,11 @@ replay(LogState, InitAcc, Fun) -> ...
 
 **Sub-deliverables:**
 - [x] **4a** — Seed genesis SX file authoring: `next/genesis/manifest.sx` + `next/genesis/activity-types/create.sx`. Manifest uses bare parenthesised paths (data lists, not `(list ...)` calls — consumed by `parse`, not `eval`). `next/tests/genesis_parse.sh` (5 cases).
-- [ ] **4b** — Author remaining activity-types (Update / Delete) + object-types (DefineActivity, DefineObject, DefineProjection, …) + projections, validators, codecs, sig-suites, audience predicates
+- [x] **4b-act** — Remaining activity-types: `update.sx` + `delete.sx`, manifest updated, parse tests (10 cases total in `genesis_parse.sh`)
+- [ ] **4b-obj** — Object-types: SXArtifact, Note, Tombstone, DefineActivity, DefineObject, DefineProjection, DefineValidator, DefineCodec, DefineSigSuite, Snapshot
+- [ ] **4b-proj** — Projections: activity-log, by-type, by-actor, by-object, actor-state, define-registry, audience-graph
+- [ ] **4b-vld** — Validators: envelope-shape, signature, type-schema
+- [ ] **4b-cod** — Codecs + sig-suites + audience predicates
 - [ ] **4c** — `bootstrap:read_genesis/1` in Erlang: walk the manifest, file-read each referenced .sx, return parsed forms
 - [ ] **4d** — `bootstrap:build_genesis/1` + `bootstrap:verify_genesis/1`: compute bundle CID over the read forms via the host `cid:to_string` substrate; verify against a stored `bundle.cidhash`
 - [ ] **4e** — `bootstrap:load_genesis/1`: register parsed definitions into the in-memory registry (depends on Step 5)
@@ -951,6 +955,7 @@ A few things still under-specified; resolve as work begins.
 Newest first. One line per sub-deliverable commit. Erlang conformance gate
 (`bash lib/erlang/conformance.sh`) must remain 729/729 on every entry.
 
+- **2026-05-27** — Step 4b-act: bootstrap activity-types complete — `update.sx` (Update verb, requires :object CID + :patch) + `delete.sx` (Delete verb, requires :object CID) authored as DefineActivity forms matching the Create shape. Manifest updated; `next/tests/genesis_parse.sh` 10/10. Step 4b broken into act/obj/proj/vld/cod sub-deliverables on the plan. Erlang conformance 729/729.
 - **2026-05-27** — Step 4a: genesis bundle seeded. `next/genesis/manifest.sx` (GenesisManifest with eight section keys, only `:activity-types` populated for now) + `next/genesis/activity-types/create.sx` (DefineActivity{Create} with :schema/:semantics SX bodies). `next/tests/genesis_parse.sh` 5/5. Step 3b parked behind a substrate-level term-codec gap — Blockers note added under Step 3; in-memory log from 3a unblocks Step 5+ which only need the API surface. Erlang conformance 729/729.
 - **2026-05-27** — Step 3a: `log:open/2 append/2 tip/1 replay/3 entries/1` over an in-memory state (per-actor seq, replay in append order, round-trip activities). `next/tests/log_memory.sh` 12/12. Pivoted from on-disk in this iteration: this port's `atom_to_list`/`integer_to_list` return SX strings rather than Erlang charlists, `binary_to_list` is unregistered, and `$X` char literals decode to nil — so a term codec needs a workaround. Captured as the Step 3b risk note in the plan. Erlang conformance 729/729.
 - **2026-05-26** — Step 2c: `envelope:verify_signature/2` — time-aware key lookup over `public_keys` (created ≤ published < superseded_at), MAC recompute via `crypto:hash(sha256, KeyMaterial ++ canonical_bytes)`, compared against `signature.value`. Returns ok or one of `no_signature | no_key_id | no_published | no_keys | no_active_key | bad_signature`. `next/tests/envelope_sig.sh` 11/11 pass. Erlang conformance 729/729.