diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index d1cade0b..f970aa7f 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -14,7 +14,7 @@ jobs:
     needs: build_sdist
     strategy:
       matrix:
-        os: [ubuntu-latest, ubuntu-24.04-arm, windows-latest, macos-latest]
+        os: [ubuntu-latest, ubuntu-24.04-arm, windows-latest, windows-11-arm, macos-latest]
 
     steps:
       - name: Checkout
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 4b6a553c..e044b746 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -50,6 +50,10 @@ jobs:
           - ubuntu-24.04-arm
           - macos-latest
           - windows-latest
+          - windows-11-arm
+        exclude:
+          - os: windows-11-arm
+            py: "3.8"
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # was: actions/checkout@v6
       - name: Setup python for test ${{ matrix.py }}
diff --git a/src/ngram_search.h b/src/ngram_search.h
index c00f782a..6e97eda2 100644
--- a/src/ngram_search.h
+++ b/src/ngram_search.h
@@ -231,13 +231,13 @@ struct ngram_search_s {
      * linked lists of CHANs, one list per word, and each CHAN in this
      * set is allocated only on demand and freed if inactive.
      */
-    root_chan_t *root_chan;  /**< Roots of search tree. */
-    int32 n_root_chan_alloc; /**< Number of root_chan allocated */
-    int32 n_root_chan;       /**< Number of valid root_chan */
-    int32 n_nonroot_chan;    /**< Number of valid non-root channels */
-    int32 max_nonroot_chan;  /**< Maximum possible number of non-root channels */
-    root_chan_t *rhmm_1ph;   /**< Root HMMs for single-phone words */
-
+    root_chan_t *root_chan;     /**< Roots of search tree. */
+    int32 n_root_chan_alloc;    /**< Number of root_chan allocated */
+    int32 n_root_chan;          /**< Number of valid root_chan */
+    int32 n_nonroot_chan;       /**< Number of valid non-root channels */
+    int32 max_nonroot_chan;     /**< Maximum possible number of non-root channels */
+    root_chan_t *rhmm_1ph;      /**< Root HMMs for single-phone words */
+    root_chan_t ***root_lookup; /**< Root channel lookup table */
     /**
      * Channels associated with a given word (only used for right
      * contexts, single-phone words in fwdtree search, and word HMMs
diff --git a/src/ngram_search_fwdtree.c b/src/ngram_search_fwdtree.c
index 586cf05d..67a93f70 100644
--- a/src/ngram_search_fwdtree.c
+++ b/src/ngram_search_fwdtree.c
@@ -79,6 +79,10 @@ init_search_tree(ngram_search_t *ngs)
     ndiph = 0;
     ngs->n_1ph_words = 0;
     n_ci = bin_mdef_n_ciphone(ps_search_acmod(ngs)->mdef);
+    /* Allocate and zero-initialize the root channel lookup table indexed by
+     * (ciphone, ci2phone) for constant-time root channel lookup.
+     */
+    ngs->root_lookup = (root_chan_t ***)ckd_calloc_2d(n_ci, n_ci, sizeof(root_chan_t *));
     /* Allocate a bitvector with flags for each possible diphone. */
     dimap = bitvec_alloc(n_ci * n_ci);
     for (w = 0; w < n_words; w++) {
@@ -175,7 +179,7 @@ create_search_channels(ngram_search_t *ngs)
 {
     chan_t *hmm;
     root_chan_t *rhmm;
-    int32 w, i, j, p, ph, tmatid;
+    int32 w, j, p, ph, tmatid;
     int32 n_words;
     dict_t *dict = ps_search_dict(ngs);
     dict2pid_t *d2p = ps_search_dict2pid(ngs);
@@ -210,12 +214,14 @@ create_search_channels(ngram_search_t *ngs)
          * allocate one if not found. */
         ciphone = dict_first_phone(dict, w);
         ci2phone = dict_second_phone(dict, w);
-        for (i = 0; i < ngs->n_root_chan; ++i) {
-            if (ngs->root_chan[i].ciphone == ciphone
-                && ngs->root_chan[i].ci2phone == ci2phone)
-                break;
-        }
-        if (i == ngs->n_root_chan) {
+
+        /* Lookup an existing root channel for the first two CI phones.
+         * This replaces the previous O(n_root_chan) linear search with
+         * an O(1) table lookup.
+         */
+        rhmm = ngs->root_lookup[ciphone][ci2phone];
+
+        if (rhmm == NULL) {
             rhmm = &(ngs->root_chan[ngs->n_root_chan]);
             rhmm->hmm.tmatid = bin_mdef_pid2tmatid(ps_search_acmod(ngs)->mdef, ciphone);
             /* Begin with CI phone?  Not sure this makes a difference... */
@@ -223,10 +229,10 @@ create_search_channels(ngram_search_t *ngs)
                 bin_mdef_pid2ssid(ps_search_acmod(ngs)->mdef, ciphone);
             rhmm->ciphone = ciphone;
             rhmm->ci2phone = ci2phone;
+            /* Cache the newly created root channel for constant-time lookups. */
+            ngs->root_lookup[ciphone][ci2phone] = rhmm;
             ngs->n_root_chan++;
         }
-        else
-            rhmm = &(ngs->root_chan[i]);
 
         E_DEBUG("word %s rhmm %d\n", dict_wordstr(dict, w), rhmm - ngs->root_chan);
         /* Now, rhmm = root channel for w.  Go on to remaining phones */