diff --git a/src/lib/context.ts b/src/lib/context.ts
index 81f986b..d63cae3 100644
--- a/src/lib/context.ts
+++ b/src/lib/context.ts
@@ -15,6 +15,34 @@ import { RootProcess, SwOptions } from "./types";
 const DEFAULT_SHIM_ROOT_NAME = ".node-spawn-wrap";
 const SHIM_ROOT_ENV_VAR = "SPAWN_WRAP_SHIM_ROOT";
 
+export enum SwMode {
+  /**
+   * Run the wrapped module in the same process as the wrapper.
+   *
+   * A `runMain` function will be available on the wrapper API.
+   * Changing the exec arguments will have no effect.
+   * The patched spawn calls will attempt to reduce the number of intermediate
+   * processes. At most one intermediate process may be created to ensure that
+   * the user exec args are applied.
+   * Spawned processes without a main script will not be wrapped (e.g. `--eval`,
+   * `--interactive`, etc.)
+   */
+  SameProcess = "same-process",
+
+  /**
+   * Run the wrapped module in a subprocess of the wrapper.
+   *
+   * The wrapper must take care to manually spawn the subprocess. It gets access
+   * to its arguments through the wrapper API. It must also register the
+   * internal patcher manually (through `--require ...`) to continue watching
+   * the subtree.
+   * All the node processes can be wrapped this way.
+   * This mode requires more work but grants more control other the
+   * subprocesses.
+   */
+  SubProcess = "sub-process",
+}
+
 /**
  * Spawn wrap context.
  */
@@ -27,7 +55,7 @@ export interface SwContext<D = any> {
   /**
    * Absolute system path for the corresponding dependencies.
    */
-  readonly deps: Readonly<Record<"debug" | "foregroundChild" | "isWindows" | "pathEnvVar" | "parseNodeOptions" | "signalExit", string>>;
+  readonly deps: Readonly<Record<"debug" | "foregroundChild" | "pathEnvVar" | "parseNodeOptions" | "signalExit", string>>;
 
   /**
    * Unique key identifying this context.
@@ -80,17 +108,11 @@ export interface SwContext<D = any> {
   readonly data: D;
 
   /**
-   * Run the wrapper and child process in the same process.
-   *
-   * Using the same process allows to reduce memory usage and improve speed
-   * but prevents changing the node engine flags (such as
-   * `--experimental-modules`) dynamically inside the wrapper.
-   * If the spawned node process uses node engine flags, multiple processes
-   * may be used.
+   * Controls if the wrapped and wrapper modules run in the same process or not.
    *
-   * Default: `true`.
+   * See `SwMode` documentation for more information about each mode.
    */
-  readonly sameProcess: boolean;
+  readonly mode: SwMode;
 
   /**
    * Information about the root process.
@@ -108,7 +130,7 @@ interface ResolvedOptions {
   data: any;
   key: string;
   shimDir: string;
-  sameProcess: boolean;
+  mode: SwMode;
 }
 
 export function withWrapContext<R = any>(options: SwOptions, handler: (ctx: SwContext) => Promise<R>): Promise<R> {
@@ -170,7 +192,7 @@ function realpathMkdirpSync(path: string): string {
 }
 
 /**
- * Retuns the default shim root.
+ * Returns the default shim root.
  *
  * If the environment variable `SPAWN_WRAP_SHIM_ROOT` is defined, it returns
  * its value. Otherwise, it returns the directory `.node-spawn-wrap` in the
@@ -232,9 +254,9 @@ function resolveOptions(options: SwOptions): ResolvedOptions {
   );
 
   const wrapper = path.resolve(options.wrapper);
+  const mode: SwMode = options.mode;
   const data = options.data !== undefined ? JSON.parse(JSON.stringify(options.data)) : {};
   const shimRoot = options.shimRoot !== undefined ? path.resolve(options.shimRoot) : getShimRoot();
-  const sameProcess: boolean = options.sameProcess !== undefined ? options.sameProcess : true;
 
   debug("resolveOptions wrapper=%j data=%j shimRoot=%j", wrapper, data, shimRoot);
 
@@ -246,7 +268,7 @@ function resolveOptions(options: SwOptions): ResolvedOptions {
     data,
     key,
     shimDir,
-    sameProcess,
+    mode,
   };
 }
 
@@ -256,7 +278,6 @@ function resolvedOptionsToContext(resolved: ResolvedOptions): SwContext {
     deps: Object.freeze({
       debug: require.resolve("./debug"),
       foregroundChild: require.resolve("demurgos-foreground-child"),
-      isWindows: require.resolve("is-windows"),
       pathEnvVar: require.resolve("./path-env-var"),
       parseNodeOptions: require.resolve("./parse-node-options"),
       signalExit: require.resolve("signal-exit"),
@@ -268,7 +289,7 @@ function resolvedOptionsToContext(resolved: ResolvedOptions): SwContext {
     preloadScript: path.join(resolved.shimDir, "preload.js"),
     wrapper: resolved.wrapper,
     data: resolved.data,
-    sameProcess: resolved.sameProcess,
+    mode: resolved.mode,
     root: Object.freeze({
       execPath: process.execPath,
       pid: process.pid,
diff --git a/src/lib/index.ts b/src/lib/index.ts
index a1bd625..3075760 100644
--- a/src/lib/index.ts
+++ b/src/lib/index.ts
@@ -1,4 +1,4 @@
-export { SwContext } from "./context";
+export { SwContext, SwMode } from "./context";
 export { withSpawnWrap, withSpawnWrapSync } from "./local";
 export { ChildProcessProxy, ReadableStreamProxy, observeSpawn, ObserveSpawnOptions, SpawnEvent } from "./observable/index";
 export { patchInternalsWithContext, patchInternals } from "./internals";
diff --git a/src/lib/mungers/node.ts b/src/lib/mungers/node.ts
index 1637ab6..923ba4f 100644
--- a/src/lib/mungers/node.ts
+++ b/src/lib/mungers/node.ts
@@ -1,4 +1,4 @@
-import { SwContext } from "../context";
+import { SwContext, SwMode } from "../context";
 import { debug } from "../debug";
 import { getExeBasename } from "../exe-type";
 import { ParsedNodeOptions, parseNodeOptions } from "../parse-node-options";
@@ -9,18 +9,25 @@ export function mungeNode(ctx: SwContext, options: NormalizedOptions): Normalize
   const parsed: ParsedNodeOptions = parseNodeOptions(options.args);
 
   let newArgs: string[];
-  if (ctx.sameProcess) {
-    if (parsed.appArgs.length > 0) {
-      // Has a script
-      newArgs = [parsed.execPath, ...parsed.execArgs, "--", ctx.shimScript, ...parsed.appArgs];
-    } else {
-      // `--interactive`, `--eval`, `--version`, etc.
-      // Avoid wrapping these kind of invocations in same-process mode.
-      newArgs = [...options.args];
+  switch (ctx.mode) {
+    case SwMode.SameProcess: {
+      if (parsed.appArgs.length > 0) {
+        // Has a script
+        newArgs = [parsed.execPath, ...parsed.execArgs, "--", ctx.shimScript, ...parsed.appArgs];
+      } else {
+        // `--interactive`, `--eval`, `--version`, etc.
+        // Avoid wrapping these kind of invocations in same-process mode.
+        newArgs = [...options.args];
+      }
+      break;
     }
-  } else {
-    // In subProcess mode, the exec args are not applied to the wrapper process.
-    newArgs = [parsed.execPath, "--", ctx.shimScript,  ...parsed.execArgs, ...parsed.appArgs];
+    case SwMode.SubProcess: {
+      // In subProcess mode, the exec args are not applied to the wrapper process.
+      newArgs = [parsed.execPath, "--", ctx.shimScript,  ...parsed.execArgs, ...parsed.appArgs];
+      break;
+    }
+    default:
+      throw new Error(`Unknown mode: ${ctx.mode}`);
   }
 
   let newFile: string = options.file;
diff --git a/src/lib/observable/index.ts b/src/lib/observable/index.ts
index 48b188f..68d7444 100644
--- a/src/lib/observable/index.ts
+++ b/src/lib/observable/index.ts
@@ -3,8 +3,8 @@ import cp, { ChildProcess } from "child_process";
 import events from "events";
 import { Observable, Observer, Subscribable, Unsubscribable } from "rxjs";
 import { filter } from "rxjs/operators";
+import { SwMode } from "../context";
 import { Api, withSpawnWrap, WithSwOptions } from "../local";
-import { SwOptions } from "../types";
 import { ClientMessage, InfoMessage, StreamEvent } from "./protocol";
 import { RemoteSpawnClient, SpawnServer } from "./server";
 
@@ -267,7 +267,7 @@ export function observeSpawn(
           host: server.host,
           port: server.port,
         },
-        sameProcess: false,
+        mode: SwMode.SubProcess,
         api,
       };
 
diff --git a/src/lib/templates/shim-template.ts b/src/lib/templates/shim-template.ts
index 4ca521d..fa80584 100644
--- a/src/lib/templates/shim-template.ts
+++ b/src/lib/templates/shim-template.ts
@@ -22,7 +22,6 @@ const {debug} = require(context.deps.debug);
 const {removeFromPathEnv, isPathEnvName} = require(context.deps.pathEnvVar);
 const {parseNodeOptions} = require(context.deps.parseNodeOptions);
 const foregroundChild = require(context.deps.foregroundChild);
-const isWindows = require(context.deps.isWindows);
 const spawnWrap = require(context.module);
 const Module = require("module");
 const path = require("path");
@@ -51,40 +50,47 @@ function shimMain() {
 
   let args: ReadonlyArray<string>;
 
-  if (context.sameProcess) {
-    // user args: no exec args and no shim path
-    const userArgs: ReadonlyArray<string> = [process.argv[0]].concat(originalArgs);
-    const parsed: any = parseNodeOptions(userArgs);
-    if (parsed.appArgs.length === 0 || parsed.hasEval || parsed.hasInteractive) {
-      // Avoid running the wrapper in same process mode if node is used without a script
-      // Can happen for example if we intercept `node -e <...>`
-      debug("no main file!");
-      foregroundChild(process.execPath, originalArgs);
-      return;
+  switch (context.mode) {
+    case "same-process": {
+      // user args: no exec args and no shim path
+      const userArgs: ReadonlyArray<string> = [process.argv[0]].concat(originalArgs);
+      const parsed: any = parseNodeOptions(userArgs);
+      if (parsed.appArgs.length === 0 || parsed.hasEval || parsed.hasInteractive) {
+        // Avoid running the wrapper in same process mode if node is used without a script
+        // Can happen for example if we intercept `node -e <...>`
+        debug("no main file!");
+        foregroundChild(process.execPath, originalArgs);
+        return;
+      }
+      if (parsed.execArgs.length > 0) {
+        // `process.argv` starts with some non-applied exec args: we need to spawn
+        // a subprocess to apply them.
+        const fixedArgs: ReadonlyArray<string> = [
+          ...withoutTrailingDoubleDash(process.execArgv),
+          parsed.execArgs,
+          "--",
+          __filename,
+          ...parsed.appArgs,
+        ];
+        foregroundChild(process.execPath, fixedArgs);
+        return;
+      }
+      // If we reached this point, it means that we were called as:
+      // `/path/to/node ...execArgs /path/to/shim ...userAppArgs`
+      args = [...originalArgs];
+      break;
     }
-    if (parsed.execArgs.length > 0) {
-      // `process.argv` starts with some non-applied exec args: we need to spawn
-      // a subprocess to apply them.
-      const fixedArgs: ReadonlyArray<string> = [
-        ...withoutTrailingDoubleDash(process.execArgv),
-        parsed.execArgs,
-        "--",
-        __filename,
-        ...parsed.appArgs,
-      ];
-      foregroundChild(process.execPath, fixedArgs);
-      return;
+    case "sub-process": {
+      // `process.execArgv` should be empty or `--` so we only pass the user args.
+      // Which will contain the user exec args and app args.
+      // If we wanted to add it, it should be passed to withoutTrailingDoubleDash
+      // first to ensure that the user exec args are still applied.
+      args = [...originalArgs];
+      break;
+    }
+    default: {
+      throw new Error(`Unknown mode: ${context.mode}`);
     }
-    // If we reached this point, it means that we were called as:
-    // `/path/to/node ...execArgs /path/to/shim ...userAppArgs`
-    args = [...originalArgs];
-  } else {
-    // Subprocess mode
-    // `process.execArgv` should be empty or `--` so we only pass the user args.
-    // Which will contain the user exec args and app args.
-    // If we wanted to add it, it should be passed to withoutTrailingDoubleDash
-    // first to ensure that the user exec args are still applied.
-    args = [...originalArgs];
   }
 
   // This will be insert again when a process is spawned through a patched spawn.
@@ -98,7 +104,7 @@ function shimMain() {
   // Replace the shim script with the wrapper so it looks like the main
   process.argv.splice(1, 1, context.wrapper);
 
-  if (context.sameProcess) {
+  if (context.mode === "same-process") {
     spawnWrap.patchInternalsWithContext(context);
 
     function runMain(): void {
diff --git a/src/lib/types.ts b/src/lib/types.ts
index 7a71e9c..e2b6520 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -1,5 +1,5 @@
 import cp from "child_process";
-import { SwContext } from "./context";
+import { SwContext, SwMode } from "./context";
 
 export interface RootProcess {
   pid: number;
@@ -45,10 +45,11 @@ export interface SwOptions {
   shimRoot?: string;
 
   /**
-   * Try to run the wrapper and original main in the same process.
-   * If `true`, then `WrapperApi` will have a `runMain`, otherwise not.
+   * Run the wrapped and wrapper modules in the same process or not.
+   *
+   * See `SwMode` documentation for more details.
    */
-  sameProcess?: boolean;
+  mode: SwMode;
 }
 
 /**
diff --git a/test/basic.js b/test/basic.js
index ae05c84..35846b7 100644
--- a/test/basic.js
+++ b/test/basic.js
@@ -12,7 +12,7 @@ const npmFixture = require.resolve('./fixtures/npm')
 
 const WRAPPER = require.resolve('./fixtures/basic.wrapper.js')
 
-var unwrap = sw.patchInternals({ wrapper: WRAPPER })
+var unwrap = sw.patchInternals({ wrapper: WRAPPER, mode: 'same-process' })
 
 var expect = 'WRAP ["--","{{FIXTURE}}","xyz"]\n' +
   '["--"]\n' +
diff --git a/test/double-wrap.js b/test/double-wrap.js
index 8109684..5ac102a 100644
--- a/test/double-wrap.js
+++ b/test/double-wrap.js
@@ -20,13 +20,13 @@ switch (process.argv[2]) {
   case 'main':
     console.error('main', process.pid, process.execArgv.concat(argv))
     console.log('main')
-    sw.patchInternals({ wrapper: WRAPPER, data: 'first' })
+    sw.patchInternals({ wrapper: WRAPPER, data: 'first', mode: 'same-process' })
     fg(node, [__filename, 'parent'])
     break
   case 'parent':
     console.error('parent', process.pid, process.execArgv.concat(argv))
     console.log('parent')
-    sw.patchInternals({ wrapper: WRAPPER, data: 'second' })
+    sw.patchInternals({ wrapper: WRAPPER, data: 'second', mode: 'same-process' })
     fg(node, [__filename, 'child'])
     break
   case 'child':
diff --git a/test/exec-flag.js b/test/exec-flag.js
index cf1219b..05ea292 100644
--- a/test/exec-flag.js
+++ b/test/exec-flag.js
@@ -12,7 +12,7 @@ const spawn = cp.spawn
 const nodes = ['node', process.execPath]
 const WRAPPER = require.resolve('./fixtures/exec-flag.wrapper.js')
 
-sw.patchInternals({ wrapper: WRAPPER })
+sw.patchInternals({ wrapper: WRAPPER, mode: 'same-process' })
 
 t.test('try to wrap a -e invocation but it isnt wrapped', function (t) {
   nodes.forEach(function (node) {
diff --git a/test/fixtures/wrap.js b/test/fixtures/wrap.js
index 60ecd25..a7be34c 100644
--- a/test/fixtures/wrap.js
+++ b/test/fixtures/wrap.js
@@ -3,7 +3,7 @@ const { spawn } = require('child_process')
 const path = require('path')
 const sw = require('../../')
 
-sw.patchInternals({ wrapper: require.resolve('./test-shim.js') })
+sw.patchInternals({ wrapper: require.resolve('./test-shim.js'), mode: 'same-process' })
 
 spawn(path.resolve(process.argv[2]), process.argv.slice(3), {
   stdio: 'inherit'
diff --git a/test/local.js b/test/local.js
index b81ea09..7253066 100644
--- a/test/local.js
+++ b/test/local.js
@@ -8,8 +8,8 @@ function test () {
   t.test('withSpawnWrapSync', function (t) {
     t.plan(4)
 
-    const result = sw.withSpawnWrapSync({ wrapper: WRAPPER, data: { name: 'foo' } }, (fooApi) => {
-      return sw.withSpawnWrapSync({ wrapper: WRAPPER, data: { name: 'bar' } }, (barApi) => {
+    const result = sw.withSpawnWrapSync({ wrapper: WRAPPER, data: { name: 'foo' }, mode: 'same-process' }, (fooApi) => {
+      return sw.withSpawnWrapSync({ wrapper: WRAPPER, data: { name: 'bar' }, mode: 'same-process' }, (barApi) => {
         {
           const { stdout, stderr } = fooApi.spawnSync(process.execPath, [echoArgs, '1'])
           const out = stdout.toString('UTF-8')
diff --git a/test/wrap-twice.js b/test/wrap-twice.js
index ee73335..fdb8b6d 100644
--- a/test/wrap-twice.js
+++ b/test/wrap-twice.js
@@ -8,8 +8,8 @@ const WRAPPER = require.resolve('./fixtures/wrap-twice.wrapper.js')
 switch (process.argv[2]) {
   case 'main':
     console.log('main')
-    sw.patchInternals({ wrapper: WRAPPER, data: 'outer' })
-    sw.patchInternals({ wrapper: WRAPPER, data: 'inner' })
+    sw.patchInternals({ wrapper: WRAPPER, data: 'outer', mode: 'same-process' })
+    sw.patchInternals({ wrapper: WRAPPER, data: 'inner', mode: 'same-process' })
     fg(node, [__filename, 'parent'])
     break