diff --git a/lib/lua/runtime.sx b/lib/lua/runtime.sx
index 83eeb2d0..445852b2 100644
--- a/lib/lua/runtime.sx
+++ b/lib/lua/runtime.sx
@@ -41,27 +41,77 @@
           ((= op "^") (pow na nb))
           (else (error (str "lua: unknown arith op " op))))))))
 
-(define lua-add (fn (a b) (lua-num-op "+" a b)))
+(define
+  lua-get-mm
+  (fn
+    (v name)
+    (cond
+      ((not (= (type-of v) "dict")) nil)
+      (else
+        (let
+          ((mt (get v "__meta")))
+          (cond
+            ((= mt nil) nil)
+            ((not (= (type-of mt) "dict")) nil)
+            ((has-key? mt name) (get mt name))
+            (else nil)))))))
 
-(define lua-sub (fn (a b) (lua-num-op "-" a b)))
+(define
+  lua-arith
+  (fn
+    (mm op a b)
+    (cond
+      ((and (= (type-of a) "number") (= (type-of b) "number"))
+        (lua-num-op op a b))
+      ((and
+         (or (= (type-of a) "number") (= (type-of a) "string"))
+         (or (= (type-of b) "number") (= (type-of b) "string"))
+         (not (= (lua-to-number a) nil))
+         (not (= (lua-to-number b) nil)))
+        (lua-num-op op a b))
+      (else
+        (let
+          ((m (lua-get-mm a mm)))
+          (cond
+            ((not (= m nil)) (lua-first (m a b)))
+            (else
+              (let
+                ((m2 (lua-get-mm b mm)))
+                (if
+                  (not (= m2 nil))
+                  (lua-first (m2 a b))
+                  (error (str "lua: arith on " (type-of a) " " op " " (type-of b))))))))))))
 
-(define lua-mul (fn (a b) (lua-num-op "*" a b)))
+(define lua-add (fn (a b) (lua-arith "__add" "+" a b)))
 
-(define lua-div (fn (a b) (lua-num-op "/" a b)))
+(define lua-sub (fn (a b) (lua-arith "__sub" "-" a b)))
 
-(define lua-mod (fn (a b) (lua-num-op "%" a b)))
+(define lua-mul (fn (a b) (lua-arith "__mul" "*" a b)))
 
-(define lua-pow (fn (a b) (lua-num-op "^" a b)))
+(define lua-div (fn (a b) (lua-arith "__div" "/" a b)))
+
+(define lua-mod (fn (a b) (lua-arith "__mod" "%" a b)))
+
+(define lua-pow (fn (a b) (lua-arith "__pow" "^" a b)))
 
 (define
   lua-neg
   (fn
     (a)
-    (let
-      ((na (lua-to-number a)))
-      (begin
-        (when (= na nil) (error (str "lua: neg on non-number: " a)))
-        (- 0 na)))))
+    (cond
+      ((= (type-of a) "number") (- 0 a))
+      (else
+        (let
+          ((na (lua-to-number a)))
+          (cond
+            ((not (= na nil)) (- 0 na))
+            (else
+              (let
+                ((m (lua-get-mm a "__unm")))
+                (if
+                  (not (= m nil))
+                  (lua-first (m a))
+                  (error (str "lua: neg on non-number: " (type-of a))))))))))))
 
 (define
   lua-concat-coerce
@@ -76,9 +126,23 @@
   lua-concat
   (fn
     (a b)
-    (let
-      ((sa (lua-concat-coerce a)) (sb (lua-concat-coerce b)))
-      (str sa sb))))
+    (cond
+      ((and
+         (or (= (type-of a) "string") (= (type-of a) "number"))
+         (or (= (type-of b) "string") (= (type-of b) "number")))
+        (str (lua-concat-coerce a) (lua-concat-coerce b)))
+      (else
+        (let
+          ((m (lua-get-mm a "__concat")))
+          (cond
+            ((not (= m nil)) (lua-first (m a b)))
+            (else
+              (let
+                ((m2 (lua-get-mm b "__concat")))
+                (if
+                  (not (= m2 nil))
+                  (lua-first (m2 a b))
+                  (error (str "lua: concat on " (type-of a) " and " (type-of b))))))))))))
 
 (define
   lua-eq
@@ -88,6 +152,13 @@
       ((and (= a nil) (= b nil)) true)
       ((or (= a nil) (= b nil)) false)
       ((and (= (type-of a) (type-of b)) (= a b)) true)
+      ((and (= (type-of a) "dict") (= (type-of b) "dict"))
+        (let
+          ((m (lua-get-mm a "__eq")))
+          (cond
+            ((not (= m nil))
+              (let ((r (lua-first (m a b)))) (and (not (= r nil)) (not (= r false)))))
+            (else false))))
       (else false))))
 
 (define lua-neq (fn (a b) (not (lua-eq a b))))
@@ -99,9 +170,41 @@
     (cond
       ((and (= (type-of a) "number") (= (type-of b) "number")) (< a b))
       ((and (= (type-of a) "string") (= (type-of b) "string")) (< a b))
-      (else (error "lua: attempt to compare incompatible types")))))
+      (else
+        (let
+          ((m (lua-get-mm a "__lt")))
+          (cond
+            ((not (= m nil))
+              (let ((r (lua-first (m a b)))) (and (not (= r nil)) (not (= r false)))))
+            (else
+              (let
+                ((m2 (lua-get-mm b "__lt")))
+                (cond
+                  ((not (= m2 nil))
+                    (let ((r (lua-first (m2 a b)))) (and (not (= r nil)) (not (= r false)))))
+                  (else (error "lua: attempt to compare incompatible types")))))))))))
 
-(define lua-le (fn (a b) (or (lua-lt a b) (lua-eq a b))))
+(define
+  lua-le
+  (fn
+    (a b)
+    (cond
+      ((and (= (type-of a) "number") (= (type-of b) "number")) (<= a b))
+      ((and (= (type-of a) "string") (= (type-of b) "string"))
+        (or (< a b) (= a b)))
+      (else
+        (let
+          ((m (lua-get-mm a "__le")))
+          (cond
+            ((not (= m nil))
+              (let ((r (lua-first (m a b)))) (and (not (= r nil)) (not (= r false)))))
+            (else
+              (let
+                ((m2 (lua-get-mm b "__le")))
+                (cond
+                  ((not (= m2 nil))
+                    (let ((r (lua-first (m2 a b)))) (and (not (= r nil)) (not (= r false)))))
+                  (else (not (lua-lt b a))))))))))))
 
 (define lua-gt (fn (a b) (lua-lt b a)))
 
@@ -116,17 +219,22 @@
       ((= (type-of a) "list") (len a))
       ((= (type-of a) "dict")
         (let
-          ((n 0))
-          (begin
-            (define
-              count-loop
-              (fn
-                (i)
-                (if
-                  (has-key? a (str i))
-                  (begin (set! n i) (count-loop (+ i 1)))
-                  n)))
-            (count-loop 1))))
+          ((m (lua-get-mm a "__len")))
+          (cond
+            ((not (= m nil)) (lua-first (m a)))
+            (else
+              (let
+                ((n 0))
+                (begin
+                  (define
+                    count-loop
+                    (fn
+                      (i)
+                      (if
+                        (has-key? a (str i))
+                        (begin (set! n i) (count-loop (+ i 1)))
+                        n)))
+                  (count-loop 1)))))))
       (else (error (str "lua: len on non-len type: " (type-of a)))))))
 
 (define
@@ -166,9 +274,37 @@
   lua-get
   (fn
     (t k)
-    (if (= t nil) nil (let ((v (get t (str k)))) (if (= v nil) nil v)))))
+    (cond
+      ((= t nil) nil)
+      ((not (= (type-of t) "dict")) nil)
+      (else
+        (let
+          ((key (str k)))
+          (cond
+            ((has-key? t key) (get t key))
+            (else
+              (let
+                ((m (lua-get-mm t "__index")))
+                (cond
+                  ((= m nil) nil)
+                  ((= (type-of m) "dict") (lua-get m k))
+                  (else (lua-first (m t k))))))))))))
 
-(define lua-set! (fn (t k v) (dict-set! t (str k) v)))
+(define
+  lua-set!
+  (fn
+    (t k v)
+    (let
+      ((key (str k)))
+      (cond
+        ((has-key? t key) (dict-set! t key v))
+        (else
+          (let
+            ((m (lua-get-mm t "__newindex")))
+            (cond
+              ((= m nil) (dict-set! t key v))
+              ((= (type-of m) "dict") (lua-set! m k v))
+              (else (begin (m t k v) nil)))))))))
 
 (define
   lua-multi?
@@ -215,3 +351,52 @@
     (cond
       ((= (len vals) 0) (list (quote lua-multi)))
       (else (cons (quote lua-multi) (lua-pack-build vals 0))))))
+
+(define lua-setmetatable (fn (t mt) (begin (dict-set! t "__meta" mt) t)))
+
+(define
+  lua-getmetatable
+  (fn
+    (t)
+    (cond
+      ((not (= (type-of t) "dict")) nil)
+      ((has-key? t "__meta") (get t "__meta"))
+      (else nil))))
+
+(define setmetatable lua-setmetatable)
+(define getmetatable lua-getmetatable)
+
+(define
+  lua-type
+  (fn
+    (v)
+    (cond
+      ((= v nil) "nil")
+      ((= (type-of v) "number") "number")
+      ((= (type-of v) "string") "string")
+      ((= v true) "boolean")
+      ((= v false) "boolean")
+      ((= (type-of v) "dict") "table")
+      ((or (= (type-of v) "function") (= (type-of v) "lambda")) "function")
+      (else (type-of v)))))
+
+(define type lua-type)
+
+(define sx-apply-ref apply)
+
+(define
+  lua-call
+  (fn
+    (&rest args)
+    (let
+      ((f (first args)) (rargs (rest args)))
+      (cond
+        ((or (= (type-of f) "function") (= (type-of f) "lambda"))
+          (sx-apply-ref f rargs))
+        ((= (type-of f) "dict")
+          (let
+            ((m (lua-get-mm f "__call")))
+            (cond
+              ((= m nil) (error "lua: attempt to call non-function"))
+              (else (sx-apply-ref m (cons f rargs))))))
+        (else (error "lua: attempt to call non-function"))))))
diff --git a/lib/lua/test.sh b/lib/lua/test.sh
index 5bb5d6b5..f75e0262 100755
--- a/lib/lua/test.sh
+++ b/lib/lua/test.sh
@@ -594,6 +594,71 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 770)
 (eval "(lua-eval-ast \"local t = {} local s = t s.x = 42 return t.x\")")
 
+;; ── Phase 4: metatables ────────────────────────────────────────
+;; setmetatable / getmetatable
+(epoch 800)
+(eval "(lua-eval-ast \"local t = {} local r = setmetatable(t, {}) if r == t then return 1 else return 0 end\")")
+(epoch 801)
+(eval "(lua-eval-ast \"local mt = {} local t = setmetatable({}, mt) if getmetatable(t) == mt then return 1 else return 0 end\")")
+
+;; type()
+(epoch 810)
+(eval "(lua-eval-ast \"return type(1)\")")
+(epoch 811)
+(eval "(lua-eval-ast \"return type(\\\"s\\\")\")")
+(epoch 812)
+(eval "(lua-eval-ast \"return type({})\")")
+(epoch 813)
+(eval "(lua-eval-ast \"return type(nil)\")")
+(epoch 814)
+(eval "(lua-eval-ast \"return type(true)\")")
+(epoch 815)
+(eval "(lua-eval-ast \"return type(function() end)\")")
+
+;; __index
+(epoch 820)
+(eval "(lua-eval-ast \"local base = {x = 10} local t = setmetatable({}, {__index = base}) return t.x\")")
+(epoch 821)
+(eval "(lua-eval-ast \"local base = {x = 10} local t = setmetatable({y = 20}, {__index = base}) return t.x + t.y\")")
+(epoch 822)
+(eval "(lua-eval-ast \"local t = setmetatable({}, {__index = function(tbl, k) return k .. \\\"!\\\" end}) return t.hi\")")
+
+;; __newindex
+(epoch 830)
+(eval "(lua-eval-ast \"local log = {} local t = setmetatable({}, {__newindex = function(tbl, k, v) log[1] = k end}) t.foo = 1 return log[1]\")")
+
+;; Arithmetic metamethods
+(epoch 840)
+(eval "(lua-eval-ast \"local mt = {__add = function(a, b) return 99 end} local x = setmetatable({}, mt) return x + 1\")")
+(epoch 841)
+(eval "(lua-eval-ast \"local mt = {__add = function(a, b) return a.v + b.v end} local x = setmetatable({v = 3}, mt) local y = setmetatable({v = 4}, mt) return x + y\")")
+(epoch 842)
+(eval "(lua-eval-ast \"local mt = {__sub = function(a, b) return 7 end, __mul = function(a, b) return 11 end} local t = setmetatable({}, mt) return t - t + (t * t)\")")
+(epoch 843)
+(eval "(lua-eval-ast \"local mt = {__unm = function(a) return 42 end} local t = setmetatable({}, mt) return -t\")")
+(epoch 844)
+(eval "(lua-eval-ast \"local mt = {__concat = function(a, b) return \\\"cat\\\" end} local t = setmetatable({}, mt) return t .. \\\"x\\\"\")")
+
+;; Comparison metamethods
+(epoch 850)
+(eval "(lua-eval-ast \"local mt = {__eq = function(a, b) return true end} local x = setmetatable({}, mt) local y = setmetatable({}, mt) if x == y then return 1 else return 0 end\")")
+(epoch 851)
+(eval "(lua-eval-ast \"local mt = {__lt = function(a, b) return true end} local x = setmetatable({}, mt) local y = setmetatable({}, mt) if x < y then return 1 else return 0 end\")")
+(epoch 852)
+(eval "(lua-eval-ast \"local mt = {__le = function(a, b) return true end} local x = setmetatable({}, mt) local y = setmetatable({}, mt) if x <= y then return 1 else return 0 end\")")
+
+;; __call
+(epoch 860)
+(eval "(lua-eval-ast \"local mt = {__call = function(t, x) return x + 100 end} local obj = setmetatable({}, mt) return obj(5)\")")
+
+;; __len
+(epoch 870)
+(eval "(lua-eval-ast \"local mt = {__len = function(t) return 99 end} local t = setmetatable({}, mt) return #t\")")
+
+;; Classic OO pattern
+(epoch 880)
+(eval "(lua-eval-ast \"local Animal = {} Animal.__index = Animal function Animal:new(name) local o = setmetatable({name = name}, self) return o end function Animal:getName() return self.name end local a = Animal:new(\\\"Rex\\\") return a:getName()\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -899,6 +964,31 @@ check 760 "t[k]=v reads via t.foo"          '88'
 check 761 "t[concat]=v reads via t.xy"      '7'
 check 770 "reference semantics t=s"         '42'
 
+# ── Phase 4: metatables ───────────────────────────────────────
+check 800 "setmetatable returns t"          '1'
+check 801 "getmetatable roundtrip"          '1'
+check 810 "type(1)"                         '"number"'
+check 811 "type(string)"                    '"string"'
+check 812 "type({})"                        '"table"'
+check 813 "type(nil)"                       '"nil"'
+check 814 "type(true)"                      '"boolean"'
+check 815 "type(function)"                  '"function"'
+check 820 "__index table lookup"            '10'
+check 821 "__index chain + self"            '30'
+check 822 "__index as function"             '"hi!"'
+check 830 "__newindex fires"                '"foo"'
+check 840 "__add table+number"              '99'
+check 841 "__add two tables"                '7'
+check 842 "__sub + __mul chain"             '18'
+check 843 "__unm"                           '42'
+check 844 "__concat"                        '"cat"'
+check 850 "__eq"                            '1'
+check 851 "__lt"                            '1'
+check 852 "__le"                            '1'
+check 860 "__call"                          '105'
+check 870 "__len"                           '99'
+check 880 "OO pattern self:m()"             '"Rex"'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL Lua-on-SX tests passed"
diff --git a/lib/lua/transpile.sx b/lib/lua/transpile.sx
index ddb671b4..070fddb6 100644
--- a/lib/lua/transpile.sx
+++ b/lib/lua/transpile.sx
@@ -104,7 +104,9 @@
     (node)
     (let
       ((fn-ast (nth node 1)) (args (nth node 2)))
-      (cons (lua-tx fn-ast) (map lua-tx args)))))
+      (cons
+        (make-symbol "lua-call")
+        (cons (lua-tx fn-ast) (map lua-tx args))))))
 
 (define
   lua-tx-method-call
@@ -115,8 +117,10 @@
         (name (nth node 2))
         (args (nth node 3)))
       (cons
-        (list (make-symbol "lua-get") obj name)
-        (cons obj (map lua-tx args))))))
+        (make-symbol "lua-call")
+        (cons
+          (list (make-symbol "lua-get") obj name)
+          (cons obj (map lua-tx args)))))))
 
 (define
   lua-tx-field
diff --git a/plans/lua-on-sx.md b/plans/lua-on-sx.md
index 06ac655e..a99eb41b 100644
--- a/plans/lua-on-sx.md
+++ b/plans/lua-on-sx.md
@@ -60,7 +60,7 @@ Each item: implement → tests → tick box → update progress log.
 - [x] `scoreboard.json` + `scoreboard.md` baseline
 
 ### Phase 4 — metatables + error handling (next run)
-- [ ] Metatable dispatch: `__index`, `__newindex`, `__add`/`__sub`/…, `__eq`, `__lt`, `__call`, `__tostring`, `__len`
+- [x] Metatable dispatch: `__index`, `__newindex`, `__add`/`__sub`/…, `__eq`, `__lt`, `__call`, `__tostring`, `__len`
 - [ ] `pcall`/`xpcall`/`error` via handler-bind
 - [ ] Generic `for … in …`
 
@@ -82,6 +82,7 @@ Each item: implement → tests → tick box → update progress log.
 
 _Newest first. Agent appends on every commit._
 
+- 2026-04-24: lua: phase 4 — metatable dispatch (`__index`/`__newindex`/arith/compare/`__call`/`__len`), `setmetatable`/`getmetatable`/`type` globals, OO `self:method` pattern. Transpile routes all calls through `lua-call` (stashed `sx-apply-ref` to dodge user-shadowing of SX `apply`). Skipped `__tostring` (needs `tostring()` builtin). 247 total tests.
 - 2026-04-24: lua: PUC-Rio scoreboard baseline — 0/16 runnable pass (0.0%). Top modes: 14× parse error, 1× `print` undef, 1× vararg transpile. Phase 3 complete.
 - 2026-04-24: lua: conformance runner — `conformance.sh` shim + `conformance.py` (long-lived sx_server, epoch protocol, classify_error, writes scoreboard.{json,md}). 24 files classified in full run: 8 skip / 16 fail / 0 timeout.
 - 2026-04-24: lua: vendored PUC-Rio 5.1 test suite (lua5.1-tests.tar.gz from lua.org) to `lib/lua/lua-tests/` — 22 .lua files, 6304 lines; README kept for context.