diff --git a/inference/inference-core/src/commonMain/kotlin/io/kinference.core/operators/KIOperatorFactory.kt b/inference/inference-core/src/commonMain/kotlin/io/kinference.core/operators/KIOperatorFactory.kt
index 7c081523f..ddae86ca9 100755
--- a/inference/inference-core/src/commonMain/kotlin/io/kinference.core/operators/KIOperatorFactory.kt
+++ b/inference/inference-core/src/commonMain/kotlin/io/kinference.core/operators/KIOperatorFactory.kt
@@ -20,8 +20,7 @@ import io.kinference.core.operators.convolution.*
 import io.kinference.core.operators.pool.*
 import io.kinference.core.operators.quantization.*
 import io.kinference.core.operators.quantization.lstm.DynamicQuantizeLSTM
-import io.kinference.core.operators.seq.ConcatFromSequence
-import io.kinference.core.operators.seq.SplitToSequence
+import io.kinference.core.operators.seq.*
 import io.kinference.core.operators.tensor.*
 import io.kinference.graph.Graph
 import io.kinference.operator.*
@@ -125,6 +124,7 @@ object KIOperatorFactory : OperatorFactory<KIONNXData<*>> {
         "Reshape" -> Reshape(name, version, attributes, inputs, outputs)
         "ScatterElements" -> ScatterElements(name, version, attributes, inputs, outputs)
         "ScatterND" -> ScatterND(name, version, attributes, inputs, outputs)
+        "SequenceLength" -> SequenceLength(name, version, attributes, inputs, outputs)
         "Shape" -> Shape(name, version, attributes, inputs, outputs)
         "Sigmoid" -> Sigmoid(name, version, attributes, inputs, outputs)
         "Sign" -> Sign(name, version, attributes, inputs, outputs)
diff --git a/inference/inference-core/src/commonMain/kotlin/io/kinference.core/operators/seq/SequenceLength.kt b/inference/inference-core/src/commonMain/kotlin/io/kinference.core/operators/seq/SequenceLength.kt
new file mode 100644
index 000000000..9521a7a10
--- /dev/null
+++ b/inference/inference-core/src/commonMain/kotlin/io/kinference.core/operators/seq/SequenceLength.kt
@@ -0,0 +1,56 @@
+package io.kinference.core.operators.seq
+
+import io.kinference.attribute.Attribute
+import io.kinference.core.data.seq.KIONNXSequence
+import io.kinference.core.data.tensor.KITensor
+import io.kinference.core.data.tensor.asTensor
+import io.kinference.data.ONNXData
+import io.kinference.data.ONNXDataType
+import io.kinference.graph.Contexts
+import io.kinference.ndarray.arrays.LongNDArray
+import io.kinference.operator.*
+import io.kinference.protobuf.message.TensorProto
+
+sealed class SequenceLength(
+    name: String,
+    info: OperatorInfo,
+    attributes: Map<String, Attribute<Any>>,
+    inputs: List<String>,
+    outputs: List<String>
+) : Operator<KIONNXSequence, KITensor>(name, info, attributes, inputs, outputs) {
+    companion object {
+        private val DEFAULT_VERSION = VersionInfo(sinceVersion = 11)
+
+        operator fun invoke(name: String, version: Int?, attributes: Map<String, Attribute<Any>>, inputs: List<String>, outputs: List<String>): SequenceLength {
+            return when (version ?: DEFAULT_VERSION.sinceVersion) {
+                in SequenceLengthVer11.VERSION.asRange() -> SequenceLengthVer11(name, attributes, inputs, outputs)
+                else -> error("Unsupported version of SequenceLength operator: $version")
+            }
+        }
+    }
+}
+
+
+class SequenceLengthVer11 internal constructor(
+    name: String,
+    attributes: Map<String, Attribute<Any>>,
+    inputs: List<String>,
+    outputs: List<String>
+) : SequenceLength(name, INFO, attributes, inputs, outputs) {
+    companion object {
+        private val TYPE_CONSTRAINTS = ALL_DATA_TYPES
+
+        private val INPUTS_INFO = listOf(IOInfo(0, TYPE_CONSTRAINTS, "input_sequence", optional = false, onnxDataType = ONNXDataType.ONNX_SEQUENCE))
+
+        private val OUTPUTS_INFO = listOf(IOInfo(0, setOf(TensorProto.DataType.INT64), "length", optional = false))
+
+        internal val VERSION = VersionInfo(sinceVersion = 11)
+        private val INFO = OperatorInfo("SequenceLength", emptyMap(), INPUTS_INFO, OUTPUTS_INFO, VERSION, OperatorInfo.DEFAULT_DOMAIN)
+    }
+
+    override suspend fun <D : ONNXData<*, *>> apply(contexts: Contexts<D>, inputs: List<KIONNXSequence?>): List<KITensor?> {
+        val seq = inputs.first()!!.data
+        val seqLength = LongNDArray.scalar(seq.size.toLong())
+        return listOf(seqLength.asTensor("length"))
+    }
+}
diff --git a/inference/inference-tfjs/src/jsMain/kotlin/io.kinference.tfjs/operators/TFJSOperatorFactory.kt b/inference/inference-tfjs/src/jsMain/kotlin/io.kinference.tfjs/operators/TFJSOperatorFactory.kt
index 9340e4fcb..f61e0dbdf 100755
--- a/inference/inference-tfjs/src/jsMain/kotlin/io.kinference.tfjs/operators/TFJSOperatorFactory.kt
+++ b/inference/inference-tfjs/src/jsMain/kotlin/io.kinference.tfjs/operators/TFJSOperatorFactory.kt
@@ -21,8 +21,7 @@ import io.kinference.tfjs.operators.math.*
 import io.kinference.tfjs.operators.ml.*
 import io.kinference.tfjs.operators.quantization.DequantizeLinear
 import io.kinference.tfjs.operators.quantization.DynamicQuantizeLinear
-import io.kinference.tfjs.operators.seq.ConcatFromSequence
-import io.kinference.tfjs.operators.seq.SplitToSequence
+import io.kinference.tfjs.operators.seq.*
 import io.kinference.tfjs.operators.tensor.*
 
 object TFJSAttributeFactory : AttributeFactory<TFJSData<*>> {
@@ -108,6 +107,7 @@ object TFJSOperatorFactory : OperatorFactory<TFJSData<*>> {
         "Reshape" -> Reshape(name, version, attributes, inputs, outputs)
         "ScatterElements" -> ScatterElements(name, version, attributes, inputs, outputs)
         "ScatterND" -> ScatterND(name, version, attributes, inputs, outputs)
+        "SequenceLength" -> SequenceLength(name, version, attributes, inputs, outputs)
         "Shape" -> Shape(name, version, attributes, inputs, outputs)
         "Sigmoid" -> Sigmoid(name, version, attributes, inputs, outputs)
         "Sign" -> Sign(name, version, attributes, inputs, outputs)
diff --git a/inference/inference-tfjs/src/jsMain/kotlin/io.kinference.tfjs/operators/seq/SequenceLength.kt b/inference/inference-tfjs/src/jsMain/kotlin/io.kinference.tfjs/operators/seq/SequenceLength.kt
new file mode 100644
index 000000000..a429361f0
--- /dev/null
+++ b/inference/inference-tfjs/src/jsMain/kotlin/io.kinference.tfjs/operators/seq/SequenceLength.kt
@@ -0,0 +1,56 @@
+package io.kinference.tfjs.operators.seq
+
+import io.kinference.attribute.Attribute
+import io.kinference.data.ONNXData
+import io.kinference.data.ONNXDataType
+import io.kinference.graph.Contexts
+import io.kinference.ndarray.arrays.NDArrayTFJS
+import io.kinference.operator.*
+import io.kinference.protobuf.message.TensorProto
+import io.kinference.tfjs.data.seq.TFJSSequence
+import io.kinference.tfjs.data.tensors.TFJSTensor
+import io.kinference.tfjs.data.tensors.asTensor
+
+sealed class SequenceLength(
+    name: String,
+    info: OperatorInfo,
+    attributes: Map<String, Attribute<Any>>,
+    inputs: List<String>,
+    outputs: List<String>
+) : Operator<TFJSSequence, TFJSTensor>(name, info, attributes, inputs, outputs) {
+    companion object {
+        private val DEFAULT_VERSION = VersionInfo(sinceVersion = 11)
+
+        operator fun invoke(name: String, version: Int?, attributes: Map<String, Attribute<Any>>, inputs: List<String>, outputs: List<String>): SequenceLength {
+            return when (version ?: DEFAULT_VERSION.sinceVersion) {
+                in SequenceLengthVer11.VERSION.asRange() -> SequenceLengthVer11(name, attributes, inputs, outputs)
+                else -> error("Unsupported version of SequenceLength operator: $version")
+            }
+        }
+    }
+}
+
+
+class SequenceLengthVer11 internal constructor(
+    name: String,
+    attributes: Map<String, Attribute<Any>>,
+    inputs: List<String>,
+    outputs: List<String>
+) : SequenceLength(name, INFO, attributes, inputs, outputs) {
+    companion object {
+        private val TYPE_CONSTRAINTS = ALL_DATA_TYPES
+
+        private val INPUTS_INFO = listOf(IOInfo(0, TYPE_CONSTRAINTS, "input_sequence", optional = false, onnxDataType = ONNXDataType.ONNX_SEQUENCE))
+
+        private val OUTPUTS_INFO = listOf(IOInfo(0, setOf(TensorProto.DataType.INT64), "length", optional = false))
+
+        internal val VERSION = VersionInfo(sinceVersion = 11)
+        private val INFO = OperatorInfo("SequenceLength", emptyMap(), INPUTS_INFO, OUTPUTS_INFO, VERSION, OperatorInfo.DEFAULT_DOMAIN)
+    }
+
+    override suspend fun <D : ONNXData<*, *>> apply(contexts: Contexts<D>, inputs: List<TFJSSequence?>): List<TFJSTensor?> {
+        val seq = inputs.first()!!.data
+        val seqLength = NDArrayTFJS.intScalar(seq.size)
+        return listOf(seqLength.asTensor("length"))
+    }
+}