diff --git a/.positai/settings.json b/.positai/settings.json
index 500757de..645911e2 100644
--- a/.positai/settings.json
+++ b/.positai/settings.json
@@ -14,6 +14,7 @@
   },
   "model": {
     "id": "claude-opus-4-6",
-    "provider": "positai"
+    "provider": "positai",
+    "thinkingEffort": "high"
   }
 }
\ No newline at end of file
diff --git a/AGENTS.md b/AGENTS.md
index 4b42e822..f01ca11f 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -34,7 +34,9 @@ binary 0/1 in an underlying `raw` object.
   before moving on to the next task.
 - Increment the `.900X` dev version suffix in `DESCRIPTION` with each
   `NEWS.md` update.
-- Check that existing tests cover all new code. (The GHA test suite uses codecov.)
+- All new and changed code must have test coverage. The GHA test suite uses
+  codecov; uncovered lines will block the PR. Cover happy paths, error
+  branches, and edge cases (e.g. early returns).
 
 ## Optimization notes
 
diff --git a/NEWS.md b/NEWS.md
index 5d1315bb..541b04d3 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -25,6 +25,8 @@
   replacing iterative R while-loop.
 - `duplicated.Splits()` uses hash-based O(n) de-duplication, replacing
   O(n²) pairwise comparison.
+- `RenumberTips.multiPhylo()` applies tip permutation in a single C++ call,
+  avoiding per-tree overhead.
 
 ## Fixes
 
diff --git a/R/RcppExports.R b/R/RcppExports.R
index 27743d54..ee96e8d0 100644
--- a/R/RcppExports.R
+++ b/R/RcppExports.R
@@ -93,6 +93,10 @@ path_lengths <- function(edge, weight, init_nas) {
     .Call(`_TreeTools_path_lengths`, edge, weight, init_nas)
 }
 
+renumber_tips_batch <- function(trees, perm, n_tip, new_labels) {
+    .Call(`_TreeTools_renumber_tips_batch`, trees, perm, n_tip, new_labels)
+}
+
 cpp_edge_to_splits <- function(edge, order, nTip) {
     .Call(`_TreeTools_cpp_edge_to_splits`, edge, order, nTip)
 }
diff --git a/R/tree_numbering.R b/R/tree_numbering.R
index 49264c46..1e95b8c3 100644
--- a/R/tree_numbering.R
+++ b/R/tree_numbering.R
@@ -665,10 +665,48 @@ RenumberTips.Splits <- function(tree, tipOrder) {
 RenumberTips.multiPhylo <- function(tree, tipOrder) {
   at <- attributes(tree)
   labelled <- !is.null(at[["TipLabel"]])
-  tree <- lapply(tree, RenumberTips.phylo, tipOrder)
-  if (labelled) {
-    at[["TipLabel"]] <- TipLabels(tipOrder)
+
+  startOrder <- if (labelled) at[["TipLabel"]] else tree[[1L]][["tip.label"]]
+  newOrder <- if (is.numeric(tipOrder)) {
+    startOrder[tipOrder]
+  } else {
+    TipLabels(tipOrder, single = TRUE)
+  }
+
+  if (identical(startOrder, newOrder)) return(tree)
+
+  if (any(duplicated(newOrder))) {
+    stop("Tree labels ",
+         paste0(newOrder[duplicated(newOrder)], collapse = ", "),
+         " repeated in `tipOrder`")
   }
+
+  if (length(startOrder) != length(newOrder)) {
+    startOnly <- setdiff(startOrder, newOrder)
+    newOnly <- setdiff(newOrder, startOrder)
+    if (length(startOnly)) {
+      stop("Tree labels and tipOrder must match.",
+           if (length(newOnly)) "\n  Missing in `tree`: ",
+           paste0(newOnly, collapse = ", "),
+           if (length(startOnly)) "\n  Missing in `tipOrder`: ",
+           paste0(startOnly, collapse = ", ")
+      )
+    }
+    newOrder <- intersect(newOrder, startOrder)
+  }
+
+  nTip <- length(startOrder)
+  matchOrder <- match(startOrder, newOrder)
+  if (any(is.na(matchOrder))) {
+    stop("Tree labels ",
+         paste0(startOrder[is.na(matchOrder)], collapse = ", "),
+         " missing from `tipOrder`")
+  }
+
+  tree <- .Call(`_TreeTools_renumber_tips_batch`, tree, matchOrder, nTip,
+                newOrder)
+
+  if (labelled) at[["TipLabel"]] <- newOrder
   attributes(tree) <- at
   tree
 }
diff --git a/src/RcppExports.cpp b/src/RcppExports.cpp
index 4cf5bd0f..123c171a 100644
--- a/src/RcppExports.cpp
+++ b/src/RcppExports.cpp
@@ -298,6 +298,20 @@ BEGIN_RCPP
     return rcpp_result_gen;
 END_RCPP
 }
+// renumber_tips_batch
+Rcpp::List renumber_tips_batch(Rcpp::List trees, const Rcpp::IntegerVector perm, int n_tip, const Rcpp::CharacterVector new_labels);
+RcppExport SEXP _TreeTools_renumber_tips_batch(SEXP treesSEXP, SEXP permSEXP, SEXP n_tipSEXP, SEXP new_labelsSEXP) {
+BEGIN_RCPP
+    Rcpp::RObject rcpp_result_gen;
+    Rcpp::RNGScope rcpp_rngScope_gen;
+    Rcpp::traits::input_parameter< Rcpp::List >::type trees(treesSEXP);
+    Rcpp::traits::input_parameter< const Rcpp::IntegerVector >::type perm(permSEXP);
+    Rcpp::traits::input_parameter< int >::type n_tip(n_tipSEXP);
+    Rcpp::traits::input_parameter< const Rcpp::CharacterVector >::type new_labels(new_labelsSEXP);
+    rcpp_result_gen = Rcpp::wrap(renumber_tips_batch(trees, perm, n_tip, new_labels));
+    return rcpp_result_gen;
+END_RCPP
+}
 // cpp_edge_to_splits
 Rcpp::RawMatrix cpp_edge_to_splits(const Rcpp::IntegerMatrix& edge, const Rcpp::IntegerVector& order, const Rcpp::IntegerVector& nTip);
 RcppExport SEXP _TreeTools_cpp_edge_to_splits(SEXP edgeSEXP, SEXP orderSEXP, SEXP nTipSEXP) {
@@ -532,6 +546,7 @@ static const R_CallMethodDef CallEntries[] = {
     {"_TreeTools_n_cherries_wrapper", (DL_FUNC) &_TreeTools_n_cherries_wrapper, 3},
     {"_TreeTools_node_depth_unrooted", (DL_FUNC) &_TreeTools_node_depth_unrooted, 4},
     {"_TreeTools_path_lengths", (DL_FUNC) &_TreeTools_path_lengths, 3},
+    {"_TreeTools_renumber_tips_batch", (DL_FUNC) &_TreeTools_renumber_tips_batch, 4},
     {"_TreeTools_cpp_edge_to_splits", (DL_FUNC) &_TreeTools_cpp_edge_to_splits, 3},
     {"_TreeTools_duplicated_splits", (DL_FUNC) &_TreeTools_duplicated_splits, 2},
     {"_TreeTools_mask_splits", (DL_FUNC) &_TreeTools_mask_splits, 1},
diff --git a/src/renumber_tips.cpp b/src/renumber_tips.cpp
new file mode 100644
index 00000000..11285483
--- /dev/null
+++ b/src/renumber_tips.cpp
@@ -0,0 +1,51 @@
+#include <Rcpp/Lightest>
+using namespace Rcpp;
+
+// Apply a precomputed tip permutation to every tree in batch.
+// Returns a plain list of modified phylo objects (shallow-cloned, with new
+// edge matrices, updated tip.label, and "preorder" downgraded to "cladewise").
+// [[Rcpp::export]]
+Rcpp::List renumber_tips_batch(
+    Rcpp::List trees,
+    const Rcpp::IntegerVector perm,
+    int n_tip,
+    const Rcpp::CharacterVector new_labels
+) {
+  const int n_trees = trees.size();
+  Rcpp::List result(n_trees);
+
+  for (int i = 0; i < n_trees; ++i) {
+    // Shallow-clone the phylo list so other components are shared
+    Rcpp::List tree_i = Rcpp::clone(
+      Rcpp::as<Rcpp::List>(trees[i])
+    );
+
+    // Clone and permute the edge matrix
+    Rcpp::IntegerMatrix edge = Rcpp::clone(
+      Rcpp::as<Rcpp::IntegerMatrix>(tree_i["edge"])
+    );
+    const int n_edge = edge.nrow();
+    for (int j = 0; j < n_edge; ++j) {
+      int& child = edge(j, 1);
+      if (child <= n_tip) {
+        child = perm[child - 1];
+      }
+    }
+    tree_i["edge"] = edge;
+
+    // Replace tip labels (shared across all output trees)
+    tree_i["tip.label"] = new_labels;
+
+    // Downgrade "preorder" to "cladewise"
+    if (tree_i.hasAttribute("order")) {
+      Rcpp::CharacterVector ord = tree_i.attr("order");
+      if (ord[0] == "preorder") {
+        tree_i.attr("order") = Rcpp::CharacterVector::create("cladewise");
+      }
+    }
+
+    result[i] = tree_i;
+  }
+
+  return result;
+}
diff --git a/tests/testthat/test-tree_numbering.R b/tests/testthat/test-tree_numbering.R
index 6aff8e2b..9e66bd75 100644
--- a/tests/testthat/test-tree_numbering.R
+++ b/tests/testthat/test-tree_numbering.R
@@ -167,6 +167,61 @@ test_that("RenumberTips() works correctly", {
     
 })
 
+test_that("RenumberTips.multiPhylo() covers edge cases", {
+  mp8 <- structure(
+    list(BalancedTree(8), PectinateTree(8)),
+    class = "multiPhylo"
+  )
+
+  # Numeric tipOrder
+  result <- RenumberTips(mp8, 8:1)
+  expect_equal(TipLabels(result[[1]]), paste0("t", 8:1))
+
+  # Early return when order matches
+  expect_identical(RenumberTips(mp8, TipLabels(mp8[[1]])), mp8)
+
+  # Duplicate error
+  expect_error(RenumberTips(mp8, rep("t1", 8)), "repeated")
+
+  # Length mismatch error
+  expect_error(RenumberTips(mp8, paste0("t", 0:5)),
+               "Missing in `tree`.*Missing in `tipOrder`")
+
+  # Missing label error
+  mp_shared <- structure(
+    list(BalancedTree(8), PectinateTree(8)),
+    TipLabel = paste0("t", 1:8),
+    class = "multiPhylo"
+  )
+  expect_error(
+    RenumberTips(mp_shared, c(paste0("t", 1:7), "t_unknown")),
+    "missing from `tipOrder`"
+  )
+})
+
+test_that("RenumberTips.multiPhylo() batch matches per-tree", {
+  set.seed(7429)
+  trees <- c(
+    replicate(50, RandomTree(12, root = TRUE), simplify = FALSE),
+    replicate(50, PectinateTree(12), simplify = FALSE)
+  )
+  class(trees) <- "multiPhylo"
+  target <- sort(TipLabels(trees[[1]]))
+
+  batch <- RenumberTips(trees, target)
+  per_tree <- structure(
+    lapply(trees, RenumberTips.phylo, target),
+    class = "multiPhylo"
+  )
+
+  for (i in seq_along(batch)) {
+    expect_equal(batch[[i]][["edge"]], per_tree[[i]][["edge"]],
+                 info = paste("tree", i))
+    expect_equal(batch[[i]][["tip.label"]], per_tree[[i]][["tip.label"]],
+                 info = paste("tree", i))
+  }
+})
+
 test_that("postorder_order() works", {
   edg7 <- BalancedTree(7)$edge
   expect_postorder(edg7[postorder_order(edg7), ])