diff --git a/.changeset/great-clouds-move.md b/.changeset/great-clouds-move.md
new file mode 100644
index 0000000000..bad7afe0d9
--- /dev/null
+++ b/.changeset/great-clouds-move.md
@@ -0,0 +1,5 @@
+---
+"@workflow/swc-plugin": patch
+---
+
+Fix class ID generation when class is bound to a variable
diff --git a/packages/swc-plugin-workflow/spec.md b/packages/swc-plugin-workflow/spec.md
index d5ff9291e6..c0f76e188b 100644
--- a/packages/swc-plugin-workflow/spec.md
+++ b/packages/swc-plugin-workflow/spec.md
@@ -481,6 +481,53 @@ export class Vector {
 }
 ```
 
+### Class Expressions with Binding Names
+
+When a class expression is assigned to a variable, the plugin uses the variable name (binding name) for registration, not the internal class name. This is important because the internal class name is only accessible inside the class body.
+
+Input:
+```javascript
+import { WORKFLOW_SERIALIZE, WORKFLOW_DESERIALIZE } from "@workflow/serde";
+
+var Bash = class _Bash {
+  constructor(command) {
+    this.command = command;
+  }
+
+  static [WORKFLOW_SERIALIZE](instance) {
+    return { command: instance.command };
+  }
+
+  static [WORKFLOW_DESERIALIZE](data) {
+    return new Bash(data.command);
+  }
+};
+```
+
+Output:
+```javascript
+import { registerSerializationClass } from "workflow/internal/class-serialization";
+import { WORKFLOW_SERIALIZE, WORKFLOW_DESERIALIZE } from "@workflow/serde";
+/**__internal_workflows{"classes":{"input.js":{"Bash":{"classId":"class//input.js//Bash"}}}}*/;
+var Bash = class _Bash {
+    constructor(command) {
+        this.command = command;
+    }
+    static [WORKFLOW_SERIALIZE](instance) {
+        return { command: instance.command };
+    }
+    static [WORKFLOW_DESERIALIZE](data) {
+        return new Bash(data.command);
+    }
+};
+registerSerializationClass("class//input.js//Bash", Bash);
+```
+
+Note that:
+- The registration uses `Bash` (the variable name), not `_Bash` (the internal class name)
+- The `classId` in the manifest also uses `Bash`
+- This ensures the registration call references a symbol that's actually in scope at module level
+
 ### File Discovery for Custom Serialization
 
 Files containing classes with custom serialization are automatically discovered for transformation, even if they don't contain `"use step"` or `"use workflow"` directives. The discovery mechanism looks for:
diff --git a/packages/swc-plugin-workflow/transform/src/lib.rs b/packages/swc-plugin-workflow/transform/src/lib.rs
index f5fded485f..549b153eb5 100644
--- a/packages/swc-plugin-workflow/transform/src/lib.rs
+++ b/packages/swc-plugin-workflow/transform/src/lib.rs
@@ -355,6 +355,10 @@ pub struct StepTransform {
     module_imports: HashSet<String>,
     // Track the current class name for static method transformations
     current_class_name: Option<String>,
+    // Track the binding name when a class expression is assigned to a variable
+    // e.g., for `var Bash = class _Bash {}`, this would be "Bash"
+    // This is needed because the internal class name (_Bash) is not in scope at module level
+    current_class_binding_name: Option<String>,
     // Track static method steps that need registration after the class declaration
     // (class_name, method_name, step_id, span)
     static_method_step_registrations: Vec<(String, String, String, swc_core::common::Span)>,
@@ -1231,6 +1235,7 @@ impl StepTransform {
             current_var_context: None,
             module_imports: HashSet::new(),
             current_class_name: None,
+            current_class_binding_name: None,
             static_method_step_registrations: Vec::new(),
             static_method_workflow_registrations: Vec::new(),
             static_step_methods_to_strip: Vec::new(),
@@ -6266,6 +6271,15 @@ impl VisitMut for StepTransform {
                                 }
                             }
                         }
+                        Expr::Class(_) => {
+                            // Track the binding name for class expressions like:
+                            // var Bash = class _Bash {}
+                            // The binding name (Bash) is what's accessible at module scope,
+                            // not the internal class name (_Bash)
+                            // We set the binding name here; it will be used when visit_mut_class_expr
+                            // is called during visit_mut_children_with below
+                            self.current_class_binding_name = Some(name.clone());
+                        }
                         _ => {}
                     }
                 }
@@ -6365,18 +6379,27 @@ impl VisitMut for StepTransform {
 
     // Handle class expressions to track class name for static methods
     fn visit_mut_class_expr(&mut self, class_expr: &mut ClassExpr) {
-        let class_name = class_expr
+        // Get the internal class name (used for current_class_name tracking)
+        let internal_class_name = class_expr
             .ident
             .as_ref()
             .map(|i| i.sym.to_string())
             .unwrap_or_else(|| "AnonymousClass".to_string());
+
+        // For serialization registration, use the binding name if available
+        // e.g., for `var Bash = class _Bash {}`, use "Bash" not "_Bash"
+        // because "_Bash" is not accessible at module scope
+        let registration_name = self
+            .current_class_binding_name
+            .take()
+            .unwrap_or_else(|| internal_class_name.clone());
+
         let old_class_name = self.current_class_name.take();
-        self.current_class_name = Some(class_name.clone());
+        self.current_class_name = Some(internal_class_name.clone());
 
         // Check if class has custom serialization methods (WORKFLOW_SERIALIZE/WORKFLOW_DESERIALIZE)
         if self.has_custom_serialization_methods(&class_expr.class) {
-            self.classes_needing_serialization
-                .insert(class_name.clone());
+            self.classes_needing_serialization.insert(registration_name);
         }
 
         // Visit the class body (this populates static_step_methods_to_strip)
@@ -6387,7 +6410,7 @@ impl VisitMut for StepTransform {
             let methods_to_strip: Vec<_> = self
                 .static_step_methods_to_strip
                 .iter()
-                .filter(|(cn, _, _)| cn == &class_name)
+                .filter(|(cn, _, _)| cn == &internal_class_name)
                 .map(|(_, mn, _)| mn.clone())
                 .collect();
 
diff --git a/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/input.js b/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/input.js
new file mode 100644
index 0000000000..9baf6d23de
--- /dev/null
+++ b/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/input.js
@@ -0,0 +1,35 @@
+// Test class expression where binding name differs from internal class name
+// e.g., `var Bash = class _Bash {}` - the registration should use "Bash", not "_Bash"
+import { WORKFLOW_SERIALIZE, WORKFLOW_DESERIALIZE } from '@workflow/serde';
+
+// Class expression with different binding name
+var Bash = class _Bash {
+  constructor(command) {
+    this.command = command;
+  }
+
+  static [WORKFLOW_SERIALIZE](instance) {
+    return { command: instance.command };
+  }
+
+  static [WORKFLOW_DESERIALIZE](data) {
+    return new Bash(data.command);
+  }
+};
+
+// Also test anonymous class expression (no internal name)
+var Shell = class {
+  constructor(cmd) {
+    this.cmd = cmd;
+  }
+
+  static [WORKFLOW_SERIALIZE](instance) {
+    return { cmd: instance.cmd };
+  }
+
+  static [WORKFLOW_DESERIALIZE](data) {
+    return new Shell(data.cmd);
+  }
+};
+
+export { Bash, Shell };
diff --git a/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-client.js b/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-client.js
new file mode 100644
index 0000000000..b9d5498766
--- /dev/null
+++ b/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-client.js
@@ -0,0 +1,36 @@
+import { registerSerializationClass } from "workflow/internal/class-serialization";
+// Test class expression where binding name differs from internal class name
+// e.g., `var Bash = class _Bash {}` - the registration should use "Bash", not "_Bash"
+import { WORKFLOW_SERIALIZE, WORKFLOW_DESERIALIZE } from '@workflow/serde';
+/**__internal_workflows{"classes":{"input.js":{"Bash":{"classId":"class//input.js//Bash"},"Shell":{"classId":"class//input.js//Shell"}}}}*/;
+// Class expression with different binding name
+var Bash = class _Bash {
+    constructor(command){
+        this.command = command;
+    }
+    static [WORKFLOW_SERIALIZE](instance) {
+        return {
+            command: instance.command
+        };
+    }
+    static [WORKFLOW_DESERIALIZE](data) {
+        return new Bash(data.command);
+    }
+};
+// Also test anonymous class expression (no internal name)
+var Shell = class {
+    constructor(cmd){
+        this.cmd = cmd;
+    }
+    static [WORKFLOW_SERIALIZE](instance) {
+        return {
+            cmd: instance.cmd
+        };
+    }
+    static [WORKFLOW_DESERIALIZE](data) {
+        return new Shell(data.cmd);
+    }
+};
+export { Bash, Shell };
+registerSerializationClass("class//input.js//Bash", Bash);
+registerSerializationClass("class//input.js//Shell", Shell);
diff --git a/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-step.js b/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-step.js
new file mode 100644
index 0000000000..b9d5498766
--- /dev/null
+++ b/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-step.js
@@ -0,0 +1,36 @@
+import { registerSerializationClass } from "workflow/internal/class-serialization";
+// Test class expression where binding name differs from internal class name
+// e.g., `var Bash = class _Bash {}` - the registration should use "Bash", not "_Bash"
+import { WORKFLOW_SERIALIZE, WORKFLOW_DESERIALIZE } from '@workflow/serde';
+/**__internal_workflows{"classes":{"input.js":{"Bash":{"classId":"class//input.js//Bash"},"Shell":{"classId":"class//input.js//Shell"}}}}*/;
+// Class expression with different binding name
+var Bash = class _Bash {
+    constructor(command){
+        this.command = command;
+    }
+    static [WORKFLOW_SERIALIZE](instance) {
+        return {
+            command: instance.command
+        };
+    }
+    static [WORKFLOW_DESERIALIZE](data) {
+        return new Bash(data.command);
+    }
+};
+// Also test anonymous class expression (no internal name)
+var Shell = class {
+    constructor(cmd){
+        this.cmd = cmd;
+    }
+    static [WORKFLOW_SERIALIZE](instance) {
+        return {
+            cmd: instance.cmd
+        };
+    }
+    static [WORKFLOW_DESERIALIZE](data) {
+        return new Shell(data.cmd);
+    }
+};
+export { Bash, Shell };
+registerSerializationClass("class//input.js//Bash", Bash);
+registerSerializationClass("class//input.js//Shell", Shell);
diff --git a/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-workflow.js b/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-workflow.js
new file mode 100644
index 0000000000..b9d5498766
--- /dev/null
+++ b/packages/swc-plugin-workflow/transform/tests/fixture/class-expression-binding-name/output-workflow.js
@@ -0,0 +1,36 @@
+import { registerSerializationClass } from "workflow/internal/class-serialization";
+// Test class expression where binding name differs from internal class name
+// e.g., `var Bash = class _Bash {}` - the registration should use "Bash", not "_Bash"
+import { WORKFLOW_SERIALIZE, WORKFLOW_DESERIALIZE } from '@workflow/serde';
+/**__internal_workflows{"classes":{"input.js":{"Bash":{"classId":"class//input.js//Bash"},"Shell":{"classId":"class//input.js//Shell"}}}}*/;
+// Class expression with different binding name
+var Bash = class _Bash {
+    constructor(command){
+        this.command = command;
+    }
+    static [WORKFLOW_SERIALIZE](instance) {
+        return {
+            command: instance.command
+        };
+    }
+    static [WORKFLOW_DESERIALIZE](data) {
+        return new Bash(data.command);
+    }
+};
+// Also test anonymous class expression (no internal name)
+var Shell = class {
+    constructor(cmd){
+        this.cmd = cmd;
+    }
+    static [WORKFLOW_SERIALIZE](instance) {
+        return {
+            cmd: instance.cmd
+        };
+    }
+    static [WORKFLOW_DESERIALIZE](data) {
+        return new Shell(data.cmd);
+    }
+};
+export { Bash, Shell };
+registerSerializationClass("class//input.js//Bash", Bash);
+registerSerializationClass("class//input.js//Shell", Shell);