diff --git a/lib/go/lex.sx b/lib/go/lex.sx
index 11621c0b..ca523a5c 100644
--- a/lib/go/lex.sx
+++ b/lib/go/lex.sx
@@ -6,7 +6,8 @@
 ;; Types:
 ;;   "ident"   — identifiers (foo, _bar, mixedCase)
 ;;   "keyword" — one of the 25 Go keywords
-;;   "int"     — integer literals (decimal only this iteration)
+;;   "int"     — integer literals (decimal, 0x.. hex, 0b.. binary, 0o.. octal,
+;;               legacy 0123 octal; underscores between digits allowed)
 ;;   "string"  — interpreted string literals "..."
 ;;   "rune"    — rune literals 'x' (single char + simple escapes)
 ;;   "op"      — operators & punctuation; :value is the literal text
@@ -100,6 +101,10 @@
         (fn
           (at)
           (when (go-asi-trigger? (gl-last)) (gl-emit! "semi" "\n" at))))
+      (define
+        gl-oct-digit?
+        (fn (c) (and (not (= c nil)) (>= c "0") (<= c "7"))))
+      (define gl-bin-digit? (fn (c) (or (= c "0") (= c "1"))))
       (define
         gl-skip-line!
         (fn
@@ -131,13 +136,37 @@
             (gl-read-ident! start))
           (slice src start pos)))
       (define
-        gl-read-digits!
+        gl-read-digit-run!
+        (fn
+          (digit?)
+          (when
+            (and (< pos src-len) (or (digit? (gl-cur)) (= (gl-cur) "_")))
+            (gl-advance! 1)
+            (gl-read-digit-run! digit?))))
+      (define
+        gl-read-number!
         (fn
           ()
-          (when
-            (and (< pos src-len) (lex-digit? (gl-cur)))
-            (gl-advance! 1)
-            (gl-read-digits!))))
+          (cond
+            (and
+              (= (gl-cur) "0")
+              (or
+                (= (gl-peek 1) "x")
+                (= (gl-peek 1) "X")))
+            (do (gl-advance! 2) (gl-read-digit-run! lex-hex-digit?))
+            (and
+              (= (gl-cur) "0")
+              (or
+                (= (gl-peek 1) "b")
+                (= (gl-peek 1) "B")))
+            (do (gl-advance! 2) (gl-read-digit-run! gl-bin-digit?))
+            (and
+              (= (gl-cur) "0")
+              (or
+                (= (gl-peek 1) "o")
+                (= (gl-peek 1) "O")))
+            (do (gl-advance! 2) (gl-read-digit-run! gl-oct-digit?))
+            :else (gl-read-digit-run! lex-digit?))))
       (define
         gl-read-string!
         (fn
@@ -343,7 +372,7 @@
             (do
               (let
                 ((start pos))
-                (gl-read-digits!)
+                (gl-read-number!)
                 (gl-emit! "int" (slice src start pos) start))
               (gl-scan!))
             (= (gl-cur) "\"")
diff --git a/lib/go/scoreboard.json b/lib/go/scoreboard.json
index 2218a633..679a6267 100644
--- a/lib/go/scoreboard.json
+++ b/lib/go/scoreboard.json
@@ -1,9 +1,9 @@
 {
   "language": "go",
-  "total_pass": 78,
-  "total": 78,
+  "total_pass": 92,
+  "total": 92,
   "suites": [
-    {"name":"lex","pass":78,"total":78,"status":"ok"},
+    {"name":"lex","pass":92,"total":92,"status":"ok"},
     {"name":"parse","pass":0,"total":0,"status":"pending"},
     {"name":"types","pass":0,"total":0,"status":"pending"},
     {"name":"eval","pass":0,"total":0,"status":"pending"},
diff --git a/lib/go/scoreboard.md b/lib/go/scoreboard.md
index 9ff8965b..5104d7db 100644
--- a/lib/go/scoreboard.md
+++ b/lib/go/scoreboard.md
@@ -1,10 +1,10 @@
 # Go-on-SX Scoreboard
 
-**Total: 78 / 78 tests passing**
+**Total: 92 / 92 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
-| ✅ | lex | 78 | 78 |
+| ✅ | lex | 92 | 92 |
 | ⬜ | parse | 0 | 0 |
 | ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |
diff --git a/lib/go/tests/lex.sx b/lib/go/tests/lex.sx
index 85e4d153..be78e0c9 100644
--- a/lib/go/tests/lex.sx
+++ b/lib/go/tests/lex.sx
@@ -68,12 +68,43 @@
 (go-test "kw: type" (tok-types "type") (list "keyword" "eof"))
 (go-test "kw: var" (tok-types "var") (list "keyword" "eof"))
 
-;; ── integer literals ──────────────────────────────────────────────
+;; ── integer literals — decimal ────────────────────────────────────
 (go-test "int: zero" (tok-values "0") (list "0" "\n" nil))
 (go-test "int: small" (tok-values "42") (list "42" "\n" nil))
 (go-test "int: bigger" (tok-values "123456") (list "123456" "\n" nil))
 (go-test "int: type" (tok-types "42") (list "int" "semi" "eof"))
 
+;; ── integer literals — prefixed + underscores (Go spec § Integer literals)
+(go-test "int: hex lower" (tok-values "0x1f") (list "0x1f" "\n" nil))
+(go-test "int: hex upper-x" (tok-values "0X1F") (list "0X1F" "\n" nil))
+(go-test
+  "int: hex mixed digits"
+  (tok-values "0xDEADbeef")
+  (list "0xDEADbeef" "\n" nil))
+(go-test "int: binary lower" (tok-values "0b1010") (list "0b1010" "\n" nil))
+(go-test "int: binary upper" (tok-values "0B1101") (list "0B1101" "\n" nil))
+(go-test "int: octal modern" (tok-values "0o755") (list "0o755" "\n" nil))
+(go-test "int: octal upper" (tok-values "0O17") (list "0O17" "\n" nil))
+(go-test "int: octal legacy" (tok-values "0755") (list "0755" "\n" nil))
+(go-test "int: hex type" (tok-types "0x1F") (list "int" "semi" "eof"))
+(go-test "int: bin type" (tok-types "0b101") (list "int" "semi" "eof"))
+(go-test
+  "int: dec underscore"
+  (tok-values "1_000_000")
+  (list "1_000_000" "\n" nil))
+(go-test
+  "int: hex underscore"
+  (tok-values "0xDEAD_BEEF")
+  (list "0xDEAD_BEEF" "\n" nil))
+(go-test
+  "int: bin underscore"
+  (tok-values "0b1010_1010")
+  (list "0b1010_1010" "\n" nil))
+(go-test
+  "int: hex then +"
+  (tok-types "0xFF + 1")
+  (list "int" "op" "int" "semi" "eof"))
+
 ;; ── string literals ───────────────────────────────────────────────
 (go-test "string: empty" (tok-values "\"\"") (list "" "\n" nil))
 (go-test "string: hello" (tok-values "\"hello\"") (list "hello" "\n" nil))
diff --git a/plans/go-on-sx.md b/plans/go-on-sx.md
index 684e982c..6d222ac8 100644
--- a/plans/go-on-sx.md
+++ b/plans/go-on-sx.md
@@ -143,9 +143,10 @@ Progress-log line → push `origin/loops/go`.
       ident/int/string/rune/{break,continue,fallthrough,return}/{++,--,),],}}.
 - [ ] Float / imaginary literals
 - [ ] Raw string literals `` `...` ``
-- [ ] Hex/octal/binary integer literals (0x… 0o… 0b…) + underscores
+- [x] Hex/octal/binary integer literals (0x… 0o… 0b…) + underscores
+      (legacy 0123 octal also accepted; consumes lex-hex-digit?)
 - [ ] Full operator set audit (47 distinct per Go spec)
-- **Acceptance:** lex/ suite at 50+ tests. Current: 78/78.
+- **Acceptance:** lex/ suite at 50+ tests. Current: 92/92.
 
 ### Phase 2 — Parser (`lib/go/parse.sx`) ⬜
 - Consume `lib/guest/core/pratt.sx` + `lib/guest/core/ast.sx`. Chisel notes
@@ -404,6 +405,10 @@ _(none yet)_
 
 _Newest first. Append one dated entry per commit._
 
+- 2026-05-27 — Phase 1 cont.: prefixed integer literals (`0x..`, `0X..`,
+  `0b..`, `0B..`, `0o..`, `0O..`, legacy `0123`) + underscore separators
+  in any digit run. Dispatch in `gl-read-number!`; consumes
+  `lex-hex-digit?` from the kit. +14 tests, lex 92/92. `[consumes-lex]`.
 - 2026-05-26 — Phase 1 first slice: `lib/go/lex.sx` tokenizer consuming
   `lib/guest/lex.sx` predicates. 25 keywords, ident/int/string/rune lits,
   line+block comments, common operators, automatic semicolon insertion per