diff --git a/lib/ocaml/runtime.sx b/lib/ocaml/runtime.sx
index 29177685..52a27d08 100644
--- a/lib/ocaml/runtime.sx
+++ b/lib/ocaml/runtime.sx
@@ -274,6 +274,19 @@
        match o with
        | None -> []
        | Some x -> [x]
+
+     let join oo =
+       match oo with
+       | None -> None
+       | Some inner -> inner
+
+     let to_result none_v o =
+       match o with
+       | None -> Error none_v
+       | Some x -> Ok x
+
+     let some x = Some x
+     let none = None
    end ;;
 
    module Result = struct
@@ -316,6 +329,21 @@
        match r with
        | Ok x -> Some x
        | Error _ -> None
+
+     let value r default =
+       match r with
+       | Ok x -> x
+       | Error _ -> default
+
+     let iter f r =
+       match r with
+       | Ok x -> f x
+       | Error _ -> ()
+
+     let fold ok_f err_f r =
+       match r with
+       | Ok x -> ok_f x
+       | Error e -> err_f e
    end ;;
 
    module String = struct
@@ -334,6 +362,16 @@
      let index_of s sub = _string_index_of s sub
    end ;;
 
+   module Bytes = struct
+     (* Thin alias of String — SX has no separate immutable byte type. *)
+     let length s = String.length s
+     let get s i = String.get s i
+     let of_string s = s
+     let to_string s = s
+     let concat sep xs = String.concat sep xs
+     let sub s i n = String.sub s i n
+   end ;;
+
    module Char = struct
      let code c = _char_code c
      let chr n = _char_chr n
diff --git a/lib/ocaml/test.sh b/lib/ocaml/test.sh
index 6d467482..404b707b 100755
--- a/lib/ocaml/test.sh
+++ b/lib/ocaml/test.sh
@@ -1064,6 +1064,26 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 3604)
 (eval "(ocaml-run-program \"let q = Queue.create () ;; Queue.push 1 q ;; Queue.push 2 q ;; Queue.length q\")")
 
+;; ── Option/Result/Bytes extensions ────────────────────────────
+(epoch 3700)
+(eval "(ocaml-run \"Option.join (Some (Some 5))\")")
+(epoch 3701)
+(eval "(ocaml-run \"Option.join None\")")
+(epoch 3702)
+(eval "(ocaml-run \"Option.to_result \\\"missing\\\" None\")")
+(epoch 3703)
+(eval "(ocaml-run \"Option.to_result \\\"missing\\\" (Some 7)\")")
+(epoch 3704)
+(eval "(ocaml-run \"Result.value (Ok 5) 0\")")
+(epoch 3705)
+(eval "(ocaml-run \"Result.value (Error \\\"e\\\") 99\")")
+(epoch 3706)
+(eval "(ocaml-run \"Result.fold (fun x -> x * 10) (fun e -> 0) (Ok 5)\")")
+(epoch 3707)
+(eval "(ocaml-run \"Bytes.length \\\"hello\\\"\")")
+(epoch 3708)
+(eval "(ocaml-run \"Bytes.concat \\\"-\\\" [\\\"a\\\";\\\"b\\\";\\\"c\\\"]\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1684,6 +1704,17 @@ check 3602 "Stack.top"                    '1'
 check 3603 "Queue.pop FIFO"               '1'
 check 3604 "Queue.length"                 '2'
 
+# ── Option/Result/Bytes extensions ─────────────────────────────
+check 3700 "Option.join nested"           '("Some" 5)'
+check 3701 "Option.join None"             '("None")'
+check 3702 "Option.to_result None"        '("Error" "missing")'
+check 3703 "Option.to_result Some"        '("Ok" 7)'
+check 3704 "Result.value Ok"              '5'
+check 3705 "Result.value Error fallback"  '99'
+check 3706 "Result.fold Ok"               '50'
+check 3707 "Bytes.length"                 '5'
+check 3708 "Bytes.concat"                 '"a-b-c"'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index dd4698bf..742efe40 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -399,6 +399,12 @@ _Newest first._
   recognise `!` as the prefix-deref of an application argument, so
   `String.concat "" (List.rev !b)` parses as `(... (deref b))`. Buffer
   uses a ref holding a string list; contents reverses and concats.
+- 2026-05-08 Phase 6 — Option/Result/Bytes extensions (+9 tests, 439
+  total). Option: join, to_result, some, none. Result: value, iter,
+  fold. Bytes: length, get, of_string, to_string, concat, sub (thin
+  alias of String — SX has no separate immutable byte type). Ordering
+  fix: Bytes module placed after String so its closures capture String
+  in scope.
 - 2026-05-08 Phase 6 — `Stack` and `Queue` modules in OCaml (+5 tests,
   430 total). Stack: ref-holding-list LIFO with push/pop/top/length/
   is_empty/clear. Queue: amortised O(1) two-list `(front, back)` queue