diff --git a/lib/content/render.sx b/lib/content/render.sx
index 124aeffb..17b65ac1 100644
--- a/lib/content/render.sx
+++ b/lib/content/render.sx
@@ -6,9 +6,9 @@
 ;; children's renderings, so (asHTML doc) / (asSx doc) are pure polymorphic
 ;; sends with no type dispatch in the SX layer.
 ;;
-;; HTML escaping happens HERE, at the boundary: text and attribute values are
-;; passed through String>>htmlEscaped (& < > "), so untrusted content cannot
-;; break out of its element. asSx wire output is not yet string-escaped (next).
+;; Escaping happens HERE, at the boundary. asHTML routes text/attrs through
+;; String>>htmlEscaped (& < > "); asSx routes them through String>>sxEscaped
+;; (\ and ") so values cannot break out of an element or an SX string literal.
 
 (define
   content-bootstrap-render!
@@ -19,6 +19,10 @@
         "String"
         "htmlEscaped"
         "htmlEscaped | out i n c | out := ''. n := self size. i := 1. [i <= n] whileTrue: [c := self at: i. (c = $&) ifTrue: [out := out , '&amp;'] ifFalse: [(c = $<) ifTrue: [out := out , '&lt;'] ifFalse: [(c = $>) ifTrue: [out := out , '&gt;'] ifFalse: [(c = $\") ifTrue: [out := out , '&quot;'] ifFalse: [out := out , c asString]]]]. i := i + 1]. ^ out")
+      (ct-def-method!
+        "String"
+        "sxEscaped"
+        "sxEscaped | out i n c | out := ''. n := self size. i := 1. [i <= n] whileTrue: [c := self at: i. (c = $\\) ifTrue: [out := out , '\\\\'] ifFalse: [(c = $\") ifTrue: [out := out , '\\\"'] ifFalse: [out := out , c asString]]. i := i + 1]. ^ out")
       (ct-def-method!
         "CtHeading"
         "asHTML"
@@ -55,20 +59,29 @@
       (ct-def-method!
         "CtHeading"
         "asSx"
-        "asSx | t | t := level printString. ^ '(h' , t , ' \"' , text , '\")'")
-      (ct-def-method! "CtText" "asSx" "asSx ^ '(p \"' , text , '\")'")
-      (ct-def-method! "CtCode" "asSx" "asSx ^ '(pre (code \"' , text , '\"))'")
-      (ct-def-method! "CtQuote" "asSx" "asSx ^ '(blockquote \"' , text , '\")'")
+        "asSx | t | t := level printString. ^ '(h' , t , ' \"' , text sxEscaped , '\")'")
+      (ct-def-method! "CtText" "asSx" "asSx ^ '(p \"' , text sxEscaped , '\")'")
+      (ct-def-method!
+        "CtCode"
+        "asSx"
+        "asSx ^ '(pre (code \"' , text sxEscaped , '\"))'")
+      (ct-def-method!
+        "CtQuote"
+        "asSx"
+        "asSx ^ '(blockquote \"' , text sxEscaped , '\")'")
       (ct-def-method!
         "CtImage"
         "asSx"
-        "asSx ^ '(img :src \"' , src , '\" :alt \"' , alt , '\")'")
-      (ct-def-method! "CtEmbed" "asSx" "asSx ^ '(iframe :src \"' , url , '\")'")
+        "asSx ^ '(img :src \"' , src sxEscaped , '\" :alt \"' , alt sxEscaped , '\")'")
+      (ct-def-method!
+        "CtEmbed"
+        "asSx"
+        "asSx ^ '(iframe :src \"' , url sxEscaped , '\")'")
       (ct-def-method! "CtDivider" "asSx" "asSx ^ '(hr)'")
       (ct-def-method!
         "CtList"
         "asSx"
-        "asSx | tag | tag := ordered ifTrue: ['ol'] ifFalse: ['ul']. ^ '(' , tag , ' ' , (items inject: '' into: [:a :x | a , '(li \"' , x , '\")']) , ')'")
+        "asSx | tag | tag := ordered ifTrue: ['ol'] ifFalse: ['ul']. ^ '(' , tag , ' ' , (items inject: '' into: [:a :x | a , '(li \"' , x sxEscaped , '\")']) , ')'")
       (ct-def-method!
         "CtDoc"
         "asSx"
diff --git a/lib/content/scoreboard.json b/lib/content/scoreboard.json
index 5f5b647a..a1204ca7 100644
--- a/lib/content/scoreboard.json
+++ b/lib/content/scoreboard.json
@@ -2,14 +2,14 @@
   "suites": {
     "block": {"pass": 38, "fail": 0},
     "doc": {"pass": 40, "fail": 0},
-    "render": {"pass": 37, "fail": 0},
+    "render": {"pass": 42, "fail": 0},
     "api": {"pass": 26, "fail": 0},
     "store": {"pass": 29, "fail": 0},
     "crdt": {"pass": 34, "fail": 0},
     "sync": {"pass": 14, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 238,
+  "total_pass": 243,
   "total_fail": 0,
-  "total": 238
+  "total": 243
 }
diff --git a/lib/content/scoreboard.md b/lib/content/scoreboard.md
index 8b66364d..dbc3e56d 100644
--- a/lib/content/scoreboard.md
+++ b/lib/content/scoreboard.md
@@ -6,10 +6,10 @@ _Generated by `lib/content/conformance.sh`_
 |-------|-----:|-----:|------:|
 | block | 38 | 0 | 38 |
 | doc | 40 | 0 | 40 |
-| render | 37 | 0 | 37 |
+| render | 42 | 0 | 42 |
 | api | 26 | 0 | 26 |
 | store | 29 | 0 | 29 |
 | crdt | 34 | 0 | 34 |
 | sync | 14 | 0 | 14 |
 | fed | 20 | 0 | 20 |
-| **Total** | **238** | **0** | **238** |
+| **Total** | **243** | **0** | **243** |
diff --git a/lib/content/tests/render.sx b/lib/content/tests/render.sx
index b81d0a72..d4ee7b94 100644
--- a/lib/content/tests/render.sx
+++ b/lib/content/tests/render.sx
@@ -1,5 +1,5 @@
 ;; Phase 1 — render boundary. asHTML / asSx are polymorphic message sends on
-;; blocks and the document. HTML escaping happens at the boundary.
+;; blocks and the document. Escaping happens at the boundary.
 
 (st-bootstrap-classes!)
 (content-bootstrap-blocks!)
@@ -109,3 +109,27 @@
   "escape code body"
   (asHTML (mk-code "xc" "html" "<div> & </div>"))
   "<pre><code class=\"language-html\">&lt;div&gt; &amp; &lt;/div&gt;</code></pre>")
+
+;; ── asSx string-escaping (build expected via q/bs to avoid miscounts) ──
+(define q1 (str "\""))
+(define bs (str "\\"))
+(content-test
+  "asSx escapes quote"
+  (asSx (mk-text "qt" (str "say " q1 "hi" q1)))
+  (str "(p " q1 "say " bs q1 "hi" bs q1 q1 ")"))
+(content-test
+  "asSx escapes backslash"
+  (asSx (mk-text "qb" (str "a" bs "b")))
+  (str "(p " q1 "a" bs bs "b" q1 ")"))
+(content-test
+  "asSx plain unchanged"
+  (asSx (mk-text "pp" "plain"))
+  "(p \"plain\")")
+(content-test
+  "asSx escapes image attr"
+  (asSx (mk-image "im" (str "/a" q1) "x"))
+  (str "(img :src " q1 "/a" bs q1 q1 " :alt " q1 "x" q1 ")"))
+(content-test
+  "asSx escapes list item"
+  (asSx (mk-list "lq" false (list (str "i" q1) "j")))
+  (str "(ul (li " q1 "i" bs q1 q1 ")(li " q1 "j" q1 "))"))
diff --git a/plans/content-on-sx.md b/plans/content-on-sx.md
index 9413fb09..60fedc5d 100644
--- a/plans/content-on-sx.md
+++ b/plans/content-on-sx.md
@@ -19,7 +19,7 @@ injected adapter, not core.
 
 ## Status (rolling)
 
-`bash lib/content/conformance.sh` → **238/238** (Phases 1–4 COMPLETE + extensions: HTML escaping)
+`bash lib/content/conformance.sh` → **243/243** (Phases 1–4 COMPLETE + extensions: HTML + SX escaping)
 
 ## Ground rules
 
@@ -77,10 +77,15 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 
 ## Extensions (post-roadmap)
 - [x] HTML escaping at the render boundary (`String>>htmlEscaped`: & < > ")
-- [ ] asSx wire string-escaping (" and \ in SX string literals)
+- [x] asSx wire string-escaping (`String>>sxEscaped`: \ and " in SX literals)
 
 ## Progress log
 
+- 2026-06-07 — Extension: asSx wire string-escaping. Added `String>>sxEscaped`
+  (escapes `\`→`\\` then `"`→`\"`) and routed every `asSx` text/attr/list-item
+  through it, so the SX wire format stays valid when content contains quotes or
+  backslashes. +5 render tests (expected strings built from `q`/`bs` helpers to
+  avoid escaping miscounts). Suite 243/243.
 - 2026-06-07 — Extension: HTML escaping at the render boundary. Added
   `String>>htmlEscaped` (recursive char walk escaping & < > ", order-safe so &
   isn't double-escaped) and routed every `asHTML` text/attr through it — heading,