diff --git a/next/genesis/manifest.sx b/next/genesis/manifest.sx
index 607197f2..8e9b8a6d 100644
--- a/next/genesis/manifest.sx
+++ b/next/genesis/manifest.sx
@@ -21,7 +21,16 @@
   :activity-types ("activity-types/create.sx"
     "activity-types/update.sx"
     "activity-types/delete.sx")
-  :object-types ()
+  :object-types ("object-types/sx-artifact.sx"
+    "object-types/note.sx"
+    "object-types/tombstone.sx"
+    "object-types/define-activity.sx"
+    "object-types/define-object.sx"
+    "object-types/define-projection.sx"
+    "object-types/define-validator.sx"
+    "object-types/define-codec.sx"
+    "object-types/define-sig-suite.sx"
+    "object-types/snapshot.sx")
   :projections ()
   :validators ()
   :codecs ()
diff --git a/next/genesis/object-types/define-activity.sx b/next/genesis/object-types/define-activity.sx
new file mode 100644
index 00000000..a4699c95
--- /dev/null
+++ b/next/genesis/object-types/define-activity.sx
@@ -0,0 +1,12 @@
+;; next/genesis/object-types/define-activity.sx
+;;
+;; Meta-object that registers a new activity verb. Published as
+;; Create{DefineActivity{...}}; the define-registry projection
+;; folds it into the activity-types registry. Per design §5.
+
+(DefineObject
+  :name "DefineActivity"
+  :doc "Activity-type registration. :name is the verb (e.g.\n        \"Pin\"); :schema is an SX predicate over activity\n        envelopes; :semantics is an optional state-fold body."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :name)) (not (nil? (-> obj :schema))))))
diff --git a/next/genesis/object-types/define-codec.sx b/next/genesis/object-types/define-codec.sx
new file mode 100644
index 00000000..dcead7a2
--- /dev/null
+++ b/next/genesis/object-types/define-codec.sx
@@ -0,0 +1,15 @@
+;; next/genesis/object-types/define-codec.sx
+;;
+;; Meta-object that registers a content codec — an encode/decode
+;; pair. The bootstrap bundle ships dag-cbor, raw, and dag-json
+;; codecs; new codecs can be added via Create{DefineCodec{...}}.
+
+(DefineObject
+  :name "DefineCodec"
+  :doc "Codec registration. :name identifies the codec ('dag-cbor',\n        'raw', 'dag-json', ...); :encode and :decode are the\n        SX bodies the kernel calls when serialising / parsing\n        artifacts under this codec."
+  :schema (fn
+    (obj)
+    (and
+      (string? (-> obj :name))
+      (not (nil? (-> obj :encode)))
+      (not (nil? (-> obj :decode))))))
diff --git a/next/genesis/object-types/define-object.sx b/next/genesis/object-types/define-object.sx
new file mode 100644
index 00000000..1ee7566a
--- /dev/null
+++ b/next/genesis/object-types/define-object.sx
@@ -0,0 +1,12 @@
+;; next/genesis/object-types/define-object.sx
+;;
+;; Meta-object that registers a new object-type. Bootstrap-level —
+;; runtime registration of new object types (e.g. DefineSubscription
+;; in the Step 9b smoke test) flows through this.
+
+(DefineObject
+  :name "DefineObject"
+  :doc "Object-type registration. :name is the type tag (e.g.\n        \"PinSpec\"); :schema is an SX predicate over object\n        forms of that type."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :name)) (not (nil? (-> obj :schema))))))
diff --git a/next/genesis/object-types/define-projection.sx b/next/genesis/object-types/define-projection.sx
new file mode 100644
index 00000000..31bac635
--- /dev/null
+++ b/next/genesis/object-types/define-projection.sx
@@ -0,0 +1,16 @@
+;; next/genesis/object-types/define-projection.sx
+;;
+;; Meta-object that registers a new projection. The projection
+;; scheduler (Step 7) spawns one gen_server per registered
+;; projection and feeds activities through its :fold body in
+;; sandbox mode.
+
+(DefineObject
+  :name "DefineProjection"
+  :doc "Projection registration. :name is the projection key;\n        :initial-state is the empty state value; :fold is the\n        pure (state activity) -> state function evaluated in\n        sandbox mode per activity."
+  :schema (fn
+    (obj)
+    (and
+      (string? (-> obj :name))
+      (not (nil? (-> obj :initial-state)))
+      (not (nil? (-> obj :fold))))))
diff --git a/next/genesis/object-types/define-sig-suite.sx b/next/genesis/object-types/define-sig-suite.sx
new file mode 100644
index 00000000..fdb229b3
--- /dev/null
+++ b/next/genesis/object-types/define-sig-suite.sx
@@ -0,0 +1,12 @@
+;; next/genesis/object-types/define-sig-suite.sx
+;;
+;; Meta-object that registers a signature suite. Bootstrap ships
+;; rsa-sha256-2018 and ed25519-2020; the suite name maps an
+;; algorithm to a :verify body and a :key-format predicate.
+
+(DefineObject
+  :name "DefineSigSuite"
+  :doc "Signature suite registration. :name identifies the suite\n        ('rsa-sha256-2018', 'ed25519-2020', ...); :verify is the\n        SX (canonical-bytes signature key) -> bool body; the\n        envelope-signature validator dispatches by suite name."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :name)) (not (nil? (-> obj :verify))))))
diff --git a/next/genesis/object-types/define-validator.sx b/next/genesis/object-types/define-validator.sx
new file mode 100644
index 00000000..c487d508
--- /dev/null
+++ b/next/genesis/object-types/define-validator.sx
@@ -0,0 +1,12 @@
+;; next/genesis/object-types/define-validator.sx
+;;
+;; Meta-object that registers a validator predicate. The validation
+;; pipeline (Step 6) consults registered validators by name when
+;; running its stages.
+
+(DefineObject
+  :name "DefineValidator"
+  :doc "Validator registration. :name is the validator key (e.g.\n        \"envelope-shape\"); :predicate is the SX (activity) ->\n        ok|{error, R} body."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :name)) (not (nil? (-> obj :predicate))))))
diff --git a/next/genesis/object-types/note.sx b/next/genesis/object-types/note.sx
new file mode 100644
index 00000000..bc9de7c2
--- /dev/null
+++ b/next/genesis/object-types/note.sx
@@ -0,0 +1,10 @@
+;; next/genesis/object-types/note.sx
+;;
+;; Short message intended for an audience, ActivityPub-Note-compatible.
+;; Used by the Step 9b reactive smoke test (Note tagged "smoketest"
+;; matches the Topic subscription).
+
+(DefineObject
+  :name "Note"
+  :doc "Short authored message. :content is the body text;\n        :tags is a list of subscription-routable tags."
+  :schema (fn (obj) (string? (-> obj :content))))
diff --git a/next/genesis/object-types/snapshot.sx b/next/genesis/object-types/snapshot.sx
new file mode 100644
index 00000000..81786b69
--- /dev/null
+++ b/next/genesis/object-types/snapshot.sx
@@ -0,0 +1,13 @@
+;; next/genesis/object-types/snapshot.sx
+;;
+;; Projection state checkpoint. The projection scheduler emits
+;; Snapshot{projection-name, state-cid, log-seq} periodically;
+;; cold starts read the most recent Snapshot and replay only
+;; activities after :log-seq. Per design §10.5.
+
+(DefineObject
+  :name "Snapshot"
+  :doc "Projection-state checkpoint. :projection-name identifies\n        the projection; :state-cid is the content-address of\n        the snapshotted state value; :log-seq is the activity\n        sequence number the snapshot was taken at."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :projection-name)) (string? (-> obj :state-cid)))))
diff --git a/next/genesis/object-types/sx-artifact.sx b/next/genesis/object-types/sx-artifact.sx
new file mode 100644
index 00000000..3541a65d
--- /dev/null
+++ b/next/genesis/object-types/sx-artifact.sx
@@ -0,0 +1,10 @@
+;; next/genesis/object-types/sx-artifact.sx
+;;
+;; Content-addressed SX source — a library, component, or
+;; executable form published via Create{SXArtifact{...}}.
+;; Consumers reference an artifact by its CID. Per design §3.4.
+
+(DefineObject
+  :name "SXArtifact"
+  :doc "Published SX source. :source carries the form text;\n        :language is optional ('sx' by default); :imports lists\n        CIDs the artifact depends on."
+  :schema (fn (obj) (string? (-> obj :source))))
diff --git a/next/genesis/object-types/tombstone.sx b/next/genesis/object-types/tombstone.sx
new file mode 100644
index 00000000..05897fb2
--- /dev/null
+++ b/next/genesis/object-types/tombstone.sx
@@ -0,0 +1,9 @@
+;; next/genesis/object-types/tombstone.sx
+;;
+;; Replacement for an object that has been Delete'd. Lets projection
+;; folds keep a marker without retaining the deleted content.
+
+(DefineObject
+  :name "Tombstone"
+  :doc "Marker for a deleted object. :former-cid carries the CID\n        of the object that was removed. Projections fold Tombstone\n        by replacing the cached entry (not by omitting it)."
+  :schema (fn (obj) (string? (-> obj :former-cid))))
diff --git a/next/tests/genesis_parse.sh b/next/tests/genesis_parse.sh
index eb1fc5d7..6343fef3 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. 10 cases.
+# these forms directly as data. 22 cases.
 
 set -uo pipefail
 cd "$(git rev-parse --show-toplevel)"
@@ -42,6 +42,30 @@ cat > "$TMPFILE" <<'EPOCHS'
 (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))")
+(epoch 30)
+(eval "(first (parse (file-read \"next/genesis/object-types/sx-artifact.sx\")))")
+(epoch 31)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/sx-artifact.sx\")))) :name)")
+(epoch 32)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/note.sx\")))) :name)")
+(epoch 33)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/tombstone.sx\")))) :name)")
+(epoch 34)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/define-activity.sx\")))) :name)")
+(epoch 35)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/define-object.sx\")))) :name)")
+(epoch 36)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/define-projection.sx\")))) :name)")
+(epoch 37)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/define-validator.sx\")))) :name)")
+(epoch 38)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/define-codec.sx\")))) :name)")
+(epoch 39)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/define-sig-suite.sx\")))) :name)")
+(epoch 40)
+(eval "(get (apply dict (rest (parse (file-read \"next/genesis/object-types/snapshot.sx\")))) :name)")
+(epoch 41)
+(eval "(len (get (apply dict (rest (parse (file-read \"next/genesis/manifest.sx\")))) :object-types))")
 EPOCHS
 
 OUTPUT=$(timeout 30 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -75,6 +99,18 @@ 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"
+check 30 "sx-artifact.sx head form"     "DefineObject"
+check 31 "sx-artifact.sx name"          "SXArtifact"
+check 32 "note.sx name"                 "Note"
+check 33 "tombstone.sx name"            "Tombstone"
+check 34 "define-activity.sx name"      "DefineActivity"
+check 35 "define-object.sx name"        "DefineObject"
+check 36 "define-projection.sx name"    "DefineProjection"
+check 37 "define-validator.sx name"     "DefineValidator"
+check 38 "define-codec.sx name"         "DefineCodec"
+check 39 "define-sig-suite.sx name"     "DefineSigSuite"
+check 40 "snapshot.sx name"             "Snapshot"
+check 41 "manifest has 10 object-types" "10"
 
 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 5c0eca16..e3386a5e 100644
--- a/plans/fed-sx-milestone-1.md
+++ b/plans/fed-sx-milestone-1.md
@@ -246,7 +246,7 @@ 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).
 - [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
+- [x] **4b-obj** — Object-types: SXArtifact, Note, Tombstone, DefineActivity, DefineObject, DefineProjection, DefineValidator, DefineCodec, DefineSigSuite, Snapshot — 10 `DefineObject` files + manifest updated + 12 new parse tests
 - [ ] **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
@@ -955,6 +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-obj: bootstrap object-types complete — 10 `DefineObject` SX files authored (SXArtifact, Note, Tombstone, DefineActivity, DefineObject, DefineProjection, DefineValidator, DefineCodec, DefineSigSuite, Snapshot). Each carries an SX `:schema` predicate. Manifest `:object-types` populated; `next/tests/genesis_parse.sh` 22/22. Erlang conformance 729/729.
 - **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.