diff --git a/numpy/_core/src/multiarray/abstractdtypes.h b/numpy/_core/src/multiarray/abstractdtypes.h
index 4533e99b635f..b4cf1a13f673 100644
--- a/numpy/_core/src/multiarray/abstractdtypes.h
+++ b/numpy/_core/src/multiarray/abstractdtypes.h
@@ -47,6 +47,8 @@ npy_mark_tmp_array_if_pyscalar(
      * a custom DType registered, and then we should use that.
      * Further, `np.float64` is a double subclass, so must reject it.
      */
+    // TODO,NOTE: This function should be changed to do exact long checks
+    //            For NumPy 2.1!
     if (PyLong_Check(obj)
             && (PyArray_ISINTEGER(arr) || PyArray_ISOBJECT(arr))) {
         ((PyArrayObject_fields *)arr)->flags |= NPY_ARRAY_WAS_PYTHON_INT;
diff --git a/numpy/_core/src/umath/dispatching.c b/numpy/_core/src/umath/dispatching.c
index a3b9e7584434..110e2f40ab32 100644
--- a/numpy/_core/src/umath/dispatching.c
+++ b/numpy/_core/src/umath/dispatching.c
@@ -47,6 +47,7 @@
 #include "common.h"
 #include "npy_pycompat.h"
 
+#include "arrayobject.h"
 #include "dispatching.h"
 #include "dtypemeta.h"
 #include "npy_hashtable.h"
@@ -64,7 +65,7 @@ promote_and_get_info_and_ufuncimpl(PyUFuncObject *ufunc,
         PyArrayObject *const ops[],
         PyArray_DTypeMeta *signature[],
         PyArray_DTypeMeta *op_dtypes[],
-        npy_bool allow_legacy_promotion);
+        npy_bool legacy_promotion_is_possible);
 
 
 /**
@@ -759,7 +760,7 @@ promote_and_get_info_and_ufuncimpl(PyUFuncObject *ufunc,
         PyArrayObject *const ops[],
         PyArray_DTypeMeta *signature[],
         PyArray_DTypeMeta *op_dtypes[],
-        npy_bool allow_legacy_promotion)
+        npy_bool legacy_promotion_is_possible)
 {
     /*
      * Fetch the dispatching info which consists of the implementation and
@@ -828,7 +829,7 @@ promote_and_get_info_and_ufuncimpl(PyUFuncObject *ufunc,
      * However, we need to give the legacy implementation a chance here.
      * (it will modify `op_dtypes`).
      */
-    if (!allow_legacy_promotion || ufunc->type_resolver == NULL ||
+    if (!legacy_promotion_is_possible || ufunc->type_resolver == NULL ||
             (ufunc->ntypes == 0 && ufunc->userloops == NULL)) {
         /* Already tried or not a "legacy" ufunc (no loop found, return) */
         return NULL;
@@ -935,11 +936,11 @@ promote_and_get_ufuncimpl(PyUFuncObject *ufunc,
         PyArray_DTypeMeta *signature[],
         PyArray_DTypeMeta *op_dtypes[],
         npy_bool force_legacy_promotion,
-        npy_bool allow_legacy_promotion,
         npy_bool promoting_pyscalars,
         npy_bool ensure_reduce_compatible)
 {
     int nin = ufunc->nin, nargs = ufunc->nargs;
+    npy_bool legacy_promotion_is_possible = NPY_TRUE;
 
     /*
      * Get the actual DTypes we operate with by setting op_dtypes[i] from
@@ -964,11 +965,20 @@ promote_and_get_ufuncimpl(PyUFuncObject *ufunc,
              */
             Py_CLEAR(op_dtypes[i]);
         }
+        /*
+         * If the op_dtype ends up being a non-legacy one, then we cannot use
+         * legacy promotion (unless this is a python scalar).
+         */
+        if (op_dtypes[i] != NULL && !NPY_DT_is_legacy(op_dtypes[i]) && (
+                signature[i] != NULL ||  // signature cannot be a pyscalar
+                !(PyArray_FLAGS(ops[i]) & NPY_ARRAY_WAS_PYTHON_LITERAL))) {
+            legacy_promotion_is_possible = NPY_FALSE;
+        }
     }
 
     int current_promotion_state = get_npy_promotion_state();
 
-    if (force_legacy_promotion
+    if (force_legacy_promotion && legacy_promotion_is_possible
             && current_promotion_state == NPY_USE_LEGACY_PROMOTION
             && (ufunc->ntypes != 0 || ufunc->userloops != NULL)) {
         /*
@@ -986,7 +996,7 @@ promote_and_get_ufuncimpl(PyUFuncObject *ufunc,
     /* Pause warnings and always use "new" path */
     set_npy_promotion_state(NPY_USE_WEAK_PROMOTION);
     PyObject *info = promote_and_get_info_and_ufuncimpl(ufunc,
-            ops, signature, op_dtypes, allow_legacy_promotion);
+            ops, signature, op_dtypes, legacy_promotion_is_possible);
     set_npy_promotion_state(current_promotion_state);
 
     if (info == NULL) {
@@ -1032,7 +1042,7 @@ promote_and_get_ufuncimpl(PyUFuncObject *ufunc,
         Py_INCREF(signature[0]);
         return promote_and_get_ufuncimpl(ufunc,
                 ops, signature, op_dtypes,
-                force_legacy_promotion, allow_legacy_promotion,
+                force_legacy_promotion,
                 promoting_pyscalars, NPY_FALSE);
     }
 
diff --git a/numpy/_core/src/umath/dispatching.h b/numpy/_core/src/umath/dispatching.h
index c711a66688c6..9bb5fbd9b013 100644
--- a/numpy/_core/src/umath/dispatching.h
+++ b/numpy/_core/src/umath/dispatching.h
@@ -22,7 +22,6 @@ promote_and_get_ufuncimpl(PyUFuncObject *ufunc,
         PyArray_DTypeMeta *signature[],
         PyArray_DTypeMeta *op_dtypes[],
         npy_bool force_legacy_promotion,
-        npy_bool allow_legacy_promotion,
         npy_bool promote_pyscalars,
         npy_bool ensure_reduce_compatible);
 
diff --git a/numpy/_core/src/umath/stringdtype_ufuncs.cpp b/numpy/_core/src/umath/stringdtype_ufuncs.cpp
index 3135f9cbf9c0..ed9f62077589 100644
--- a/numpy/_core/src/umath/stringdtype_ufuncs.cpp
+++ b/numpy/_core/src/umath/stringdtype_ufuncs.cpp
@@ -1028,6 +1028,25 @@ all_strings_promoter(PyObject *NPY_UNUSED(ufunc),
                      PyArray_DTypeMeta *const signature[],
                      PyArray_DTypeMeta *new_op_dtypes[])
 {
+    if ((op_dtypes[0] != &PyArray_StringDType &&
+         op_dtypes[1] != &PyArray_StringDType &&
+         op_dtypes[2] != &PyArray_StringDType)) {
+        /*
+         * This promoter was triggered with only unicode arguments, so use
+         * unicode.  This can happen due to `dtype=` support which sets the
+         * output DType/signature.
+         */
+        new_op_dtypes[0] = NPY_DT_NewRef(&PyArray_UnicodeDType);
+        new_op_dtypes[1] = NPY_DT_NewRef(&PyArray_UnicodeDType);
+        new_op_dtypes[2] = NPY_DT_NewRef(&PyArray_UnicodeDType);
+        return 0;
+    }
+    if ((signature[0] == &PyArray_UnicodeDType &&
+         signature[1] == &PyArray_UnicodeDType &&
+         signature[2] == &PyArray_UnicodeDType)) {
+        /* Unicode forced, but didn't override a string input: invalid */
+        return -1;
+    }
     new_op_dtypes[0] = NPY_DT_NewRef(&PyArray_StringDType);
     new_op_dtypes[1] = NPY_DT_NewRef(&PyArray_StringDType);
     new_op_dtypes[2] = NPY_DT_NewRef(&PyArray_StringDType);
@@ -2532,6 +2551,17 @@ init_stringdtype_ufuncs(PyObject *umath)
         return -1;
     }
 
+    PyArray_DTypeMeta *out_strings_promoter_dtypes[] = {
+        &PyArray_UnicodeDType,
+        &PyArray_UnicodeDType,
+        &PyArray_StringDType,
+    };
+
+    if (add_promoter(umath, "add", out_strings_promoter_dtypes, 3,
+                     all_strings_promoter) < 0) {
+        return -1;
+    }
+
     INIT_MULTIPLY(Int64, int64);
     INIT_MULTIPLY(UInt64, uint64);
 
diff --git a/numpy/_core/src/umath/ufunc_object.c b/numpy/_core/src/umath/ufunc_object.c
index f6ad33f68016..a0acaf6573ed 100644
--- a/numpy/_core/src/umath/ufunc_object.c
+++ b/numpy/_core/src/umath/ufunc_object.c
@@ -606,7 +606,7 @@ static int
 convert_ufunc_arguments(PyUFuncObject *ufunc,
         ufunc_full_args full_args, PyArrayObject *out_op[],
         PyArray_DTypeMeta *out_op_DTypes[],
-        npy_bool *force_legacy_promotion, npy_bool *allow_legacy_promotion,
+        npy_bool *force_legacy_promotion,
         npy_bool *promoting_pyscalars,
         PyObject *order_obj, NPY_ORDER *out_order,
         PyObject *casting_obj, NPY_CASTING *out_casting,
@@ -622,7 +622,6 @@ convert_ufunc_arguments(PyUFuncObject *ufunc,
     /* Convert and fill in input arguments */
     npy_bool all_scalar = NPY_TRUE;
     npy_bool any_scalar = NPY_FALSE;
-    *allow_legacy_promotion = NPY_TRUE;
     *force_legacy_promotion = NPY_FALSE;
     *promoting_pyscalars = NPY_FALSE;
     for (int i = 0; i < nin; i++) {
@@ -657,11 +656,6 @@ convert_ufunc_arguments(PyUFuncObject *ufunc,
             break;
         }
 
-        if (!NPY_DT_is_legacy(out_op_DTypes[i])) {
-            *allow_legacy_promotion = NPY_FALSE;
-            // TODO: A subclass of int, float, complex could reach here and
-            //       it should not be flagged as "weak" if it does.
-        }
         if (PyArray_NDIM(out_op[i]) == 0) {
             any_scalar = NPY_TRUE;
         }
@@ -707,7 +701,7 @@ convert_ufunc_arguments(PyUFuncObject *ufunc,
             *promoting_pyscalars = NPY_TRUE;
         }
     }
-    if (*allow_legacy_promotion && (!all_scalar && any_scalar)) {
+    if ((!all_scalar && any_scalar)) {
         *force_legacy_promotion = should_use_min_scalar(nin, out_op, 0, NULL);
     }
 
@@ -2351,8 +2345,7 @@ reducelike_promote_and_resolve(PyUFuncObject *ufunc,
     }
 
     PyArrayMethodObject *ufuncimpl = promote_and_get_ufuncimpl(ufunc,
-            ops, signature, operation_DTypes, NPY_FALSE, NPY_TRUE,
-            NPY_FALSE, NPY_TRUE);
+            ops, signature, operation_DTypes, NPY_FALSE, NPY_FALSE, NPY_TRUE);
     if (evil_ndim_mutating_hack) {
         ((PyArrayObject_fields *)out)->nd = 0;
     }
@@ -4433,13 +4426,12 @@ ufunc_generic_fastcall(PyUFuncObject *ufunc,
     npy_bool subok = NPY_TRUE;
     int keepdims = -1;  /* We need to know if it was passed */
     npy_bool force_legacy_promotion;
-    npy_bool allow_legacy_promotion;
     npy_bool promoting_pyscalars;
     if (convert_ufunc_arguments(ufunc,
             /* extract operand related information: */
             full_args, operands,
             operand_DTypes,
-            &force_legacy_promotion, &allow_legacy_promotion,
+            &force_legacy_promotion,
             &promoting_pyscalars,
             /* extract general information: */
             order_obj, &order,
@@ -4460,7 +4452,7 @@ ufunc_generic_fastcall(PyUFuncObject *ufunc,
      */
     PyArrayMethodObject *ufuncimpl = promote_and_get_ufuncimpl(ufunc,
             operands, signature,
-            operand_DTypes, force_legacy_promotion, allow_legacy_promotion,
+            operand_DTypes, force_legacy_promotion,
             promoting_pyscalars, NPY_FALSE);
     if (ufuncimpl == NULL) {
         goto fail;
@@ -5790,22 +5782,20 @@ ufunc_at(PyUFuncObject *ufunc, PyObject *args)
         operand_DTypes[0] = NPY_DTYPE(PyArray_DESCR(op1_array));
         Py_INCREF(operand_DTypes[0]);
         int force_legacy_promotion = 0;
-        int allow_legacy_promotion = NPY_DT_is_legacy(operand_DTypes[0]);
 
         if (op2_array != NULL) {
             tmp_operands[1] = op2_array;
             operand_DTypes[1] = NPY_DTYPE(PyArray_DESCR(op2_array));
             Py_INCREF(operand_DTypes[1]);
-            allow_legacy_promotion &= NPY_DT_is_legacy(operand_DTypes[1]);
             tmp_operands[2] = tmp_operands[0];
             operand_DTypes[2] = operand_DTypes[0];
             Py_INCREF(operand_DTypes[2]);
 
-            if (allow_legacy_promotion && ((PyArray_NDIM(op1_array) == 0)
-                                           != (PyArray_NDIM(op2_array) == 0))) {
-                    /* both are legacy and only one is 0-D: force legacy */
-                    force_legacy_promotion = should_use_min_scalar(2, tmp_operands, 0, NULL);
-                }
+            if ((PyArray_NDIM(op1_array) == 0)
+                    != (PyArray_NDIM(op2_array) == 0)) {
+                /* both are legacy and only one is 0-D: force legacy */
+                force_legacy_promotion = should_use_min_scalar(2, tmp_operands, 0, NULL);
+            }
         }
         else {
             tmp_operands[1] = tmp_operands[0];
@@ -5816,7 +5806,7 @@ ufunc_at(PyUFuncObject *ufunc, PyObject *args)
 
         ufuncimpl = promote_and_get_ufuncimpl(ufunc, tmp_operands, signature,
                         operand_DTypes, force_legacy_promotion,
-                        allow_legacy_promotion, NPY_FALSE, NPY_FALSE);
+                        NPY_FALSE, NPY_FALSE);
         if (ufuncimpl == NULL) {
             for (int i = 0; i < 3; i++) {
                 Py_XDECREF(signature[i]);
@@ -6058,7 +6048,6 @@ py_resolve_dtypes_generic(PyUFuncObject *ufunc, npy_bool return_context,
     set_npy_promotion_state(NPY_USE_WEAK_PROMOTION);
 
     npy_bool promoting_pyscalars = NPY_FALSE;
-    npy_bool allow_legacy_promotion = NPY_TRUE;
 
     if (_get_fixed_signature(ufunc, NULL, signature_obj, signature) < 0) {
         goto finish;
@@ -6091,9 +6080,6 @@ py_resolve_dtypes_generic(PyUFuncObject *ufunc, npy_bool return_context,
             }
             DTypes[i] = NPY_DTYPE(descr);
             Py_INCREF(DTypes[i]);
-            if (!NPY_DT_is_legacy(DTypes[i])) {
-                allow_legacy_promotion = NPY_FALSE;
-            }
         }
          /* Explicitly allow int, float, and complex for the "weak" types. */
         else if (descr_obj == (PyObject *)&PyLong_Type) {
@@ -6149,7 +6135,7 @@ py_resolve_dtypes_generic(PyUFuncObject *ufunc, npy_bool return_context,
     if (!reduction) {
         ufuncimpl = promote_and_get_ufuncimpl(ufunc,
                 dummy_arrays, signature, DTypes, NPY_FALSE,
-                allow_legacy_promotion, promoting_pyscalars, NPY_FALSE);
+                promoting_pyscalars, NPY_FALSE);
         if (ufuncimpl == NULL) {
             goto finish;
         }
diff --git a/numpy/_core/tests/test_stringdtype.py b/numpy/_core/tests/test_stringdtype.py
index 228b5e949cfd..10367d1cd88d 100644
--- a/numpy/_core/tests/test_stringdtype.py
+++ b/numpy/_core/tests/test_stringdtype.py
@@ -828,6 +828,31 @@ def test_add_promoter(string_list):
         assert_array_equal(op + arr, lresult)
         assert_array_equal(arr + op, rresult)
 
+    # The promoter should be able to handle things if users pass `dtype=`
+    res = np.add("hello", string_list, dtype=StringDType)
+    assert res.dtype == StringDType()
+
+    # The promoter should not kick in if users override the input,
+    # which means arr is cast, this fails because of the unknown length.
+    with pytest.raises(TypeError, match="cannot cast dtype"):
+        np.add(arr, "add", signature=("U", "U", None), casting="unsafe")
+
+    # But it must simply reject the following:
+    with pytest.raises(TypeError, match=".*did not contain a loop"):
+        np.add(arr, "add", signature=(None, "U", None))
+
+    with pytest.raises(TypeError, match=".*did not contain a loop"):
+        np.add("a", "b", signature=("U", "U", StringDType))
+
+
+def test_add_no_legacy_promote_with_signature():
+    # Possibly misplaced, but useful to test with string DType.  We check that
+    # if there is clearly no loop found, a stray `dtype=` doesn't break things
+    # Regression test for the bad error in gh-26735
+    # (If legacy promotion is gone, this can be deleted...)
+    with pytest.raises(TypeError, match=".*did not contain a loop"):
+        np.add("3", 6, dtype=StringDType)
+
 
 def test_add_promoter_reduce():
     # Exact TypeError could change, but ensure StringDtype doesn't match