diff --git a/crates/calc/src/eval.rs b/crates/calc/src/eval.rs
index abef54f..39c725c 100644
--- a/crates/calc/src/eval.rs
+++ b/crates/calc/src/eval.rs
@@ -54,6 +54,10 @@ pub trait Host {
     fn random(&mut self) -> f64;
     /// Called when a volatile or dynamic-reference function is used.
     fn note_volatile(&mut self) {}
+    /// The spill range of the dynamic array anchored at `anchor` (`None`: it doesn't spill).
+    fn spill_range(&mut self, sheet: usize, anchor: CellRef) -> Option<RangeRef> {
+        self.workbook().sheet(sheet)?.spill_ranges.get(&anchor).copied()
+    }
     /// Values of a block, row-major. Hosts can override with a sparse fast path.
     fn range_values(&mut self, sheet: usize, range: RangeRef) -> Vec<Value> {
         range.iter().map(|c| self.cell_value(sheet, c)).collect()
@@ -322,6 +326,19 @@ impl<'h> Evaluator<'h> {
     }
 
     fn unary(&mut self, op: UnOp, x: &Expr) -> Ev {
+        if op == UnOp::Spill {
+            return match self.eval(x) {
+                Ev::R(areas) => match areas.as_slice() {
+                    [a] if a.range.is_single() => match self.host.spill_range(a.sheet, a.range.start) {
+                        Some(range) => Ev::R(vec![Area { sheet: a.sheet, range }]),
+                        None => err(CellError::Ref),
+                    },
+                    _ => err(CellError::Ref),
+                },
+                Ev::V(Value::Error(e)) => err(e),
+                _ => err(CellError::Ref),
+            };
+        }
         if op == UnOp::At {
             let ev = self.eval(x);
             return match ev {
@@ -343,7 +360,7 @@ impl<'h> Evaluator<'h> {
                 UnOp::Neg => Value::number(-n),
                 UnOp::Plus => Value::number(n),
                 UnOp::Percent => Value::number(n / 100.0),
-                UnOp::At => Value::number(n),
+                UnOp::At | UnOp::Spill => Value::number(n),
             },
             op == UnOp::Plus,
         ))
diff --git a/crates/calc/src/recalc.rs b/crates/calc/src/recalc.rs
index 13b47c4..500dec2 100644
--- a/crates/calc/src/recalc.rs
+++ b/crates/calc/src/recalc.rs
@@ -225,6 +225,26 @@ impl Host for PassHost<'_> {
     fn workbook(&self) -> &Workbook {
         self.wb
     }
+    fn spill_range(&mut self, sheet: usize, anchor: CellRef) -> Option<RangeRef> {
+        let k = (sheet, anchor);
+        if !(self.pending.contains(&k) || self.results.contains_key(&k)) {
+            return self.wb.sheet(sheet)?.spill_ranges.get(&anchor).copied();
+        }
+        // Recalculated in this pass: its new array, unless something blocks it (#SPILL!).
+        self.compute(k);
+        let arr = self.spills.get(&k)?;
+        let end = CellRef::new(
+            anchor.row.saturating_add((arr.rows as u32).saturating_sub(1)),
+            anchor.col.saturating_add((arr.cols as u32).saturating_sub(1)),
+        );
+        let range = RangeRef::new(anchor, end);
+        let sh = self.wb.sheet(sheet)?;
+        let blocked = end.row >= gridcraft_core::MAX_ROWS
+            || end.col >= gridcraft_core::MAX_COLS
+            || sh.cells.iter_range(range).any(|(c, cell)| c != anchor && (cell.formula.is_some() || !cell.value.is_empty()))
+            || sh.merges.iter().any(|m| m.intersects(&range));
+        (!blocked).then_some(range)
+    }
     fn cell_value(&mut self, sheet: usize, c: CellRef) -> Value {
         let k = (sheet, c);
         if self.pending.contains(&k) || self.results.contains_key(&k) {
diff --git a/crates/calc/src/tests.rs b/crates/calc/src/tests.rs
index 67db083..535585f 100644
--- a/crates/calc/src/tests.rs
+++ b/crates/calc/src/tests.rs
@@ -33,6 +33,40 @@ impl T {
     }
 }
 
+#[test]
+fn spill_range_operator() {
+    let mut t = T::new();
+    t.set("A1", "3");
+    t.set("B1", "=SEQUENCE(A1)");
+    t.set("C1", "=SUM(B1#)");
+    t.set("C2", "=ROWS(B1#)");
+    assert_eq!((t.num("C1"), t.num("C2")), (6.0, 3.0));
+    // Growing and shrinking the spill recalculates its users.
+    t.set("A1", "5");
+    assert_eq!((t.num("C1"), t.num("C2")), (15.0, 5.0));
+    t.set("A1", "2");
+    assert_eq!((t.num("C1"), t.num("C2")), (3.0, 2.0));
+    // A blocked spill, or a cell that doesn't spill, gives #REF!.
+    t.set("B2", "x");
+    assert_eq!(t.get("C1"), Value::Error(CellError::Ref));
+    t.set("B2", "");
+    assert_eq!(t.num("C1"), 3.0);
+    t.set("D1", "=SUM(A1#)");
+    assert_eq!(t.get("D1"), Value::Error(CellError::Ref));
+    // Through a defined name.
+    t.wb.names.push(gridcraft_model::DefinedName {
+        name: "Seq".into(),
+        scope: None,
+        formula: "Sheet1!$B$1#".into(),
+        comment: String::new(),
+        hidden: false,
+    });
+    t.set("E1", "=SUM(Seq)*10");
+    assert_eq!(t.num("E1"), 30.0);
+    t.set("A1", "4");
+    assert_eq!(t.num("E1"), 100.0);
+}
+
 #[test]
 fn arithmetic_and_dependencies() {
     let mut t = T::new();
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index f3e36cd..61c21b4 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -110,6 +110,23 @@ fn formatting_and_styles() {
     s.execute("home.cellStyle", json!({"range": "D1", "name": "Good"})).unwrap();
 }
 
+#[test]
+fn spill_references_roundtrip_through_xlsx() {
+    let mut s = s();
+    s.execute("cell.set", json!({"cell": "B1", "input": "=SEQUENCE(4)"})).unwrap();
+    s.execute("cell.set", json!({"cell": "C1", "input": "=sum(b1#)"})).unwrap();
+    s.execute("formulas.defineName", json!({"name": "Seq", "refersTo": "=Sheet1!$B$1#"})).unwrap();
+    s.execute("cell.set", json!({"cell": "C2", "input": "=MAX(Seq)"})).unwrap();
+    assert_eq!(s.execute("cell.get", json!({"cell": "C1"})).unwrap()["formula"], "=SUM(B1#)");
+    assert_eq!((v(&s, "C1"), v(&s, "C2")), (Value::Number(10.0), Value::Number(4.0)));
+    let r = s.execute("file.saveBytes", json!({"format": "xlsx"})).unwrap();
+    let b64 = r["base64"].as_str().unwrap().to_string();
+    s.execute("file.open", json!({"name": "x.xlsx", "base64": b64})).unwrap();
+    assert_eq!(s.execute("cell.get", json!({"cell": "C1"})).unwrap()["formula"], "=SUM(B1#)");
+    assert_eq!(s.doc().unwrap().wb.names[0].formula, "Sheet1!$B$1#");
+    assert_eq!((v(&s, "C1"), v(&s, "C2")), (Value::Number(10.0), Value::Number(4.0)));
+}
+
 #[test]
 fn tables_and_structured_refs() {
     let mut s = s();
diff --git a/crates/formula/src/ast.rs b/crates/formula/src/ast.rs
index 51e5068..39f2511 100644
--- a/crates/formula/src/ast.rs
+++ b/crates/formula/src/ast.rs
@@ -88,6 +88,9 @@ pub enum UnOp {
     Percent,
     /// Implicit intersection `@`.
     At,
+    /// Spill range operator `A1#`: the whole spill range of the dynamic array anchored at the
+    /// cell (`ANCHORARRAY` in files).
+    Spill,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
diff --git a/crates/formula/src/lexer.rs b/crates/formula/src/lexer.rs
index b6143ba..14b45d9 100644
--- a/crates/formula/src/lexer.rs
+++ b/crates/formula/src/lexer.rs
@@ -124,6 +124,11 @@ pub fn tokenize(src: &str) -> Result<Vec<Token>, LexError> {
                 push(&mut out, Tok::Sheet(a, b), j + 1);
                 i = j + 1;
             }
+            '#' if out.last().is_some_and(|t: &Token| t.end == start && matches!(t.tok, Tok::Word(_))) => {
+                // Spill range operator right after a reference: `A1#`.
+                push(&mut out, Tok::Op("#"), i + 1);
+                i += 1;
+            }
             '#' => {
                 // Error literal, or #-prefixed struct specifier (only inside [] which we lex as Struct).
                 let rest = src.get(start..).unwrap_or("");
diff --git a/crates/formula/src/parser.rs b/crates/formula/src/parser.rs
index f501402..b92e2e6 100644
--- a/crates/formula/src/parser.rs
+++ b/crates/formula/src/parser.rs
@@ -223,7 +223,14 @@ impl Parser {
             Tok::LBrace => self.array(),
             Tok::Func(name) => {
                 let name = normalize_function_name(&name);
-                let args = self.args()?;
+                let mut args = self.args()?;
+                // Files write `A1#` as `_xlfn.ANCHORARRAY(A1)`.
+                if name == "ANCHORARRAY"
+                    && let [Expr::Ref(Reference { kind: RefKind::Cell(_), .. })] = args.as_slice()
+                    && let Some(r) = args.pop()
+                {
+                    return Ok(Expr::Unary(UnOp::Spill, Box::new(r)));
+                }
                 Ok(Expr::Call(name, args))
             }
             Tok::Sheet(a, b) => {
@@ -263,7 +270,12 @@ impl Parser {
                 self.next();
                 return Ok(Expr::Ref(Reference { sheet, kind: RefKind::Range(a, b) }));
             }
-            return Ok(Expr::Ref(Reference { sheet, kind: RefKind::Cell(a) }));
+            let cell = Expr::Ref(Reference { sheet, kind: RefKind::Cell(a) });
+            if *self.peek() == Tok::Op("#") {
+                self.next();
+                return Ok(Expr::Unary(UnOp::Spill, Box::new(cell)));
+            }
+            return Ok(cell);
         }
         let second = match self.peek_at(1) {
             Tok::Word(w2) => Some(w2.clone()),
diff --git a/crates/formula/src/printer.rs b/crates/formula/src/printer.rs
index 0aa223e..12e785f 100644
--- a/crates/formula/src/printer.rs
+++ b/crates/formula/src/printer.rs
@@ -186,6 +186,13 @@ fn write_expr(s: &mut String, e: &Expr, r1c1: Option<CellRef>) {
                 write_expr(s, x, r1c1);
                 s.push('%');
             }
+            UnOp::Spill => {
+                write_expr(s, x, r1c1);
+                // A reference that became #REF! (its sheet or cell was deleted) stays `#REF!`.
+                if !matches!(**x, Expr::Error(_)) {
+                    s.push('#');
+                }
+            }
         },
         Expr::Binary(op, a, b) => {
             write_expr(s, a, r1c1);
diff --git a/crates/formula/src/tests.rs b/crates/formula/src/tests.rs
index ff84a5b..7ad8262 100644
--- a/crates/formula/src/tests.rs
+++ b/crates/formula/src/tests.rs
@@ -52,6 +52,22 @@ fn normalises() {
     assert_eq!(rt("'Sheet1'!A1"), "Sheet1!A1");
 }
 
+#[test]
+fn spill_operator() {
+    for f in ["A1#", "Sheet1!$D$1#", "SUM(B2#)", "'My Sheet'!A1#*2", "ROWS(A1#)+1", "IF(A1,#N/A,#REF!)"] {
+        assert_eq!(rt(f), f);
+    }
+    assert!(matches!(parse("A1#").unwrap(), Expr::Unary(UnOp::Spill, _)));
+    // Files spell it ANCHORARRAY.
+    assert_eq!(rt("_xlfn.ANCHORARRAY(Sheet1!$D$1)"), "Sheet1!$D$1#");
+    assert_eq!(rt("SUM(ANCHORARRAY(B2))"), "SUM(B2#)");
+    // Only a cell can spill.
+    assert!(parse("A1:B2#").is_err());
+    assert!(parse("Name#").is_err());
+    // Deleting the anchor's sheet leaves #REF!.
+    assert_eq!(print(&crate::adjust::delete_sheet(parse("SUM(Data!A1#)").unwrap(), "Data")), "SUM(#REF!)");
+}
+
 #[test]
 fn precedence() {
     let e = parse("1+2*3").unwrap();
diff --git a/crates/xlsx/src/fmla.rs b/crates/xlsx/src/fmla.rs
index eee516b..b4298c9 100644
--- a/crates/xlsx/src/fmla.rs
+++ b/crates/xlsx/src/fmla.rs
@@ -27,6 +27,8 @@ fn expr_to_file(e: Expr) -> String {
             Some(n) => Expr::Call(n, args),
             None => Expr::Call(name, args),
         },
+        // Files have no `#` operator: Excel writes `A1#` as `_xlfn.ANCHORARRAY(A1)`.
+        Expr::Unary(gridcraft_formula::UnOp::Spill, r) => Expr::Call("_xlfn.ANCHORARRAY".into(), vec![*r]),
         other => other,
     });
     gridcraft_formula::print(&e)
@@ -45,6 +47,13 @@ pub fn from_file(text: &str) -> String {
 mod tests {
     use super::*;
 
+    #[test]
+    fn spill_references() {
+        assert_eq!(to_file(&Formula::new("SUM(Sheet1!$D$1#)+B2#")), "SUM(_xlfn.ANCHORARRAY(Sheet1!$D$1))+_xlfn.ANCHORARRAY(B2)");
+        assert_eq!(text_to_file("=Sheet1!$D$1#"), "_xlfn.ANCHORARRAY(Sheet1!$D$1)");
+        assert_eq!(from_file("SUM(_xlfn.ANCHORARRAY(Sheet1!$D$1))+_xlfn.ANCHORARRAY(B2)"), "SUM(Sheet1!$D$1#)+B2#");
+    }
+
     #[test]
     fn prefixes() {
         assert_eq!(to_file(&Formula::new("XLOOKUP(1,A:A,B:B)+SUM(A1)")), "_xlfn.XLOOKUP(1,A:A,B:B)+SUM(A1)");