@@ -45,15 +45,21 @@ jobs:
       - name: 'Public API changes require a version bump'
         uses: brettcannon/check-for-changed-files@d85c64d17b3c1d0ac57c9cc46ea39399b0d6fa71 # v1.2.2
         with:
-          prereq-pattern: 'src/api.ts'
+          prereq-pattern: |
+            src/api.ts
+            src/types.ts
+            src/publicErrors.ts
           file-pattern: 'api/package.json'
           skip-label: 'skip api version'
           failure-message: 'The public API (${prereq-pattern}) was changed without bumping the package version in ${file-pattern} (the ${skip-label} label can be used to pass this check)'
 
       - name: 'Public API changes require a changelog entry'
         uses: brettcannon/check-for-changed-files@d85c64d17b3c1d0ac57c9cc46ea39399b0d6fa71 # v1.2.2
         with:
-          prereq-pattern: 'src/api.ts'
+          prereq-pattern: |
+            src/api.ts
+            src/types.ts
+            src/publicErrors.ts
           file-pattern: 'api/CHANGELOG.md'
           skip-label: 'skip api changelog'
           failure-message: 'The public API (${prereq-pattern}) was changed without a changelog entry in ${file-pattern} (the ${skip-label} label can be used to pass this check)'
@@ -91,12 +91,12 @@ This project has adopted the [Microsoft Open Source Code of Conduct](https://ope
 
 ## Public API package (`@vscode/python-environments`)
 
-The npm package under [`api/`](./api) is the public API facade other extensions consume. Its entry point, `api/src/main.ts`, is a **copy** of [`src/api.ts`](./src/api.ts) — the single source of truth — and is **not committed** (see [`api/.gitignore`](./api/.gitignore)).
+The npm package under [`api/`](./api) is the public API facade other extensions consume. Its sources — `api/src/main.ts`, `api/src/types.ts`, and `api/src/publicErrors.ts` — are **copies** of [`src/api.ts`](./src/api.ts), [`src/types.ts`](./src/types.ts), and [`src/publicErrors.ts`](./src/publicErrors.ts) respectively — the single sources of truth — and are **not committed** (see [`api/.gitignore`](./api/.gitignore)).
 
-- Edit the API only in `src/api.ts`. This file contains the full public surface, including the runtime `PythonEnvironments.api()` helper and `EXTENSION_ID`. `api/src/main.ts` is a build artifact — never edit or commit it.
-- `api/src/main.ts` is produced by the publish pipeline ([`build/azure-pipeline.npm.yml`](./build/azure-pipeline.npm.yml)), which copies `src/api.ts` to `api/src/main.ts` before compiling. The api package is therefore built in CI only; to build it locally, copy the file first (e.g. `cp src/api.ts api/src/main.ts`).
-- `src/api.ts` itself is validated on every PR by the extension's own lint and TypeScript compile.
-- **Versioning:** the published package version in [`api/package.json`](./api/package.json) must always match the extension version in [`package.json`](./package.json). CI enforces this via [`scripts/compare_package_versions.py`](./scripts/compare_package_versions.py). Additionally, any PR that edits `src/api.ts` must bump `api/package.json` (use the `skip api version` label to bypass) and add an entry to [`api/CHANGELOG.md`](./api/CHANGELOG.md) (use the `skip api changelog` label to bypass). When bumping, update both `package.json` files so they stay in sync.
+- Edit the public API only in `src/api.ts` (the runtime facade: `PythonEnvironments.api()` helper and `EXTENSION_ID`), `src/types.ts` (public contracts: interfaces, types, enums), and `src/publicErrors.ts` (concrete public error classes and type guards). `api/src/*.ts` files are build artifacts — never edit or commit them.
+- `api/src/main.ts`, `api/src/types.ts`, and `api/src/publicErrors.ts` are produced by the publish pipeline ([`build/azure-pipeline.npm.yml`](./build/azure-pipeline.npm.yml)), which copies `src/api.ts` to `api/src/main.ts`, `src/types.ts` to `api/src/types.ts`, and `src/publicErrors.ts` to `api/src/publicErrors.ts` before compiling. The api package is therefore built in CI only; to build it locally, copy the files first (e.g. `cp src/api.ts api/src/main.ts && cp src/types.ts api/src/types.ts && cp src/publicErrors.ts api/src/publicErrors.ts`).
+- `src/api.ts`, `src/types.ts`, and `src/publicErrors.ts` are validated on every PR by the extension's own lint and TypeScript compile.
+- **Versioning and compatibility:** the published package version in [`api/package.json`](./api/package.json) is maintained independently of the extension version in [`package.json`](./package.json) — the two do not need to match. Compatibility is based on the API shape exported by the installed Python Environments extension at runtime. Package updates must preserve backwards-compatible contracts unless the API package version intentionally communicates a breaking change; consumers should treat newly added members as optional when they may run against older installed extension versions. Any PR that edits `src/api.ts`, `src/types.ts`, or `src/publicErrors.ts` must bump `api/package.json` (use the `skip api version` label to bypass) and add an entry to [`api/CHANGELOG.md`](./api/CHANGELOG.md) (use the `skip api changelog` label to bypass).
 
 ## Questions or Issues?
 
 
@@ -155,9 +155,7 @@ The Python Environments extension was built to provide a cohesive and user frien
 
 ### API Reference (proposed)
 
-See [api.ts](https://github.com/microsoft/vscode-python-environments/blob/main/src/api.ts) for the full list of Extension APIs.
-
-To consume these APIs you can look at the example here: [API Consumption Examples](https://github.com/microsoft/vscode-python-environments/blob/main/examples/README.md)
+See [api.ts](https://github.com/microsoft/vscode-python-environments/blob/main/src/api.ts) for the runtime API facade and [types.ts](https://github.com/microsoft/vscode-python-environments/blob/main/src/types.ts) for the public API contracts. Extension authors can consume these contracts from the `@vscode/python-environments` npm package.
 
 ### Callable Commands
 
 
@@ -1,4 +1,7 @@
-# Copied from ../src/api.ts by the publish pipeline (build/azure-pipeline.npm.yml).
-# This is the published package entry point; it is produced at publish time and
-# intentionally NOT committed. src/api.ts is the single source of truth.
+# Copied from ../src/api.ts, ../src/types.ts, ../src/publicErrors.ts by the publish pipeline
+# (build/azure-pipeline.npm.yml). These are the published package sources; they are produced
+# at publish time and intentionally NOT committed. src/api.ts, src/types.ts, and
+# src/publicErrors.ts are the single sources of truth.
 src/main.ts
+src/types.ts
+src/publicErrors.ts
@@ -5,6 +5,12 @@ All notable changes to the `@vscode/python-environments` API package are documen
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.4.0]
+
+### Changed
+
+- Reorganized the package source into separate API facade, public contract, and public error modules without changing the root package exports.
+
 ## [1.3.0]
 
 ### Added
 
@@ -1,7 +1,7 @@
 {
     "name": "@vscode/python-environments",
     "description": "An API facade for the Python Environments extension in VS Code",
-    "version": "1.3.0",
+    "version": "1.4.0",
     "author": {
         "name": "Microsoft Corporation"
     },
@@ -39,9 +39,10 @@
     "scripts": {
         "prepublishOnly": "echo \"⛔ Can only publish from a secure pipeline ⛔\" && node -e \"process.exitCode = 1\"",
         "prepack": "npm run all:publish",
-        "all:publish": "git clean -xfd . && npm install && npm run compile",
+        "all:publish": "git clean -xfd . && npm install && npm run copy:sources && npm run compile",
+        "copy:sources": "node ./scripts/copy-sources.cjs",
         "compile": "npm run compile:esm && npm run compile:cjs",
-        "compile:esm": "tsc -b ./tsconfig.esm.json && mve out/esm/main.js out/esm/main.mjs",
+        "compile:esm": "tsc -b ./tsconfig.esm.json && mve out/esm/main.js out/esm/main.mjs && node -e \"require('fs').writeFileSync('out/esm/package.json', '{\\\"type\\\":\\\"module\\\"}')\"",
         "compile:cjs": "tsc -b ./tsconfig.cjs.json && mve out/cjs/main.js out/cjs/main.cjs",
         "clean": "node -e \"const fs = require('fs'); fs.rmSync('./out', { recursive: true, force: true });\"",
         "test:package": "node ./scripts/test-package.cjs"
 
@@ -0,0 +1,25 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+// Repopulates the package's generated `src` sources from the single sources of
+// truth in `../src`. These files are gitignored and are removed by the
+// `git clean -xfd .` step in `all:publish`, so they must be copied back before
+// TypeScript can compile. Mirrors the copy step in build/azure-pipeline.npm.yml.
+
+const fs = require('node:fs');
+const path = require('node:path');
+
+const packageRoot = path.resolve(__dirname, '..');
+const repoRoot = path.resolve(packageRoot, '..');
+const srcDir = path.join(packageRoot, 'src');
+
+const sources = [
+    { from: path.join(repoRoot, 'src', 'api.ts'), to: path.join(srcDir, 'main.ts') },
+    { from: path.join(repoRoot, 'src', 'types.ts'), to: path.join(srcDir, 'types.ts') },
+    { from: path.join(repoRoot, 'src', 'publicErrors.ts'), to: path.join(srcDir, 'publicErrors.ts') },
+];
+
+fs.mkdirSync(srcDir, { recursive: true });
+for (const { from, to } of sources) {
+    fs.copyFileSync(from, to);
+}
@@ -78,6 +78,23 @@ try {
     }
 
     const installedPackageRoot = path.join(testRoot, 'node_modules', '@vscode', 'python-environments');
+    const vscodeStubRoot = path.join(testRoot, 'node_modules', 'vscode');
+    fs.mkdirSync(vscodeStubRoot, { recursive: true });
+    fs.writeFileSync(path.join(vscodeStubRoot, 'package.json'), JSON.stringify({ main: 'index.js' }));
+    fs.writeFileSync(
+        path.join(vscodeStubRoot, 'index.js'),
+        [
+            "const runtimeApi = { getEnvironments: async () => [] };",
+            "const extension = {",
+            "  isActive: false,",
+            "  exports: undefined,",
+            "  packageJSON: { version: '1.37.0' },",
+            "  activate: async () => { extension.isActive = true; extension.exports = runtimeApi; return runtimeApi; },",
+            "};",
+            'exports.__runtimeApi = runtimeApi;',
+            'exports.extensions = { getExtension: () => extension };',
+        ].join('\n'),
+    );
     const installedPackageJson = JSON.parse(fs.readFileSync(path.join(installedPackageRoot, 'package.json'), 'utf8'));
     assert.strictEqual(installedPackageJson.main, './out/cjs/main.cjs');
     assert.strictEqual(installedPackageJson.types, './out/cjs/main.d.ts');
@@ -104,24 +121,52 @@ try {
     }
 
     const requireFromConsumer = createRequire(path.join(testRoot, 'legacy', 'consumer.cjs'));
+    const commonJsModule = requireFromConsumer('@vscode/python-environments');
+    assert.strictEqual(
+        typeof commonJsModule.PythonEnvironments.api,
+        'function',
+        'CommonJS consumers should load the package runtime facade',
+    );
+    execFileSync(
+        process.execPath,
+        [
+            '--eval',
+            [
+                "const packageModule = require('@vscode/python-environments');",
+                "const vscode = require('vscode');",
+                "(async () => {",
+                '  const api = await packageModule.PythonEnvironments.api();',
+                '  if (api !== vscode.__runtimeApi) process.exit(1);',
+                '})().catch(() => process.exit(1));',
+            ].join('\n'),
+        ],
+        {
+            cwd: path.join(testRoot, 'legacy'),
+            encoding: 'utf8',
+        },
+    );
     assert.strictEqual(
         canonicalPath(requireFromConsumer.resolve('@vscode/python-environments')),
         canonicalPath(path.join(installedPackageRoot, installedPackageJson.exports.require.default)),
         'CommonJS consumers should resolve the packaged CommonJS entry point',
     );
 
-    const esmEntryPoint = execFileSync(
+    const esmModuleCheck = execFileSync(
         process.execPath,
-        ['--input-type=module', '--eval', "console.log(import.meta.resolve('@vscode/python-environments'))"],
+        [
+            '--input-type=module',
+            '--eval',
+            "const packageModule = await import('@vscode/python-environments'); const vscode = await import('vscode'); if (typeof packageModule.PythonEnvironments.api !== 'function') process.exit(1); const api = await packageModule.PythonEnvironments.api(); if (api !== vscode.default.__runtimeApi) process.exit(1); console.log(import.meta.resolve('@vscode/python-environments'));",
+        ],
         {
             cwd: path.join(testRoot, 'modern'),
             encoding: 'utf8',
         },
     ).trim();
     assert.strictEqual(
-        canonicalPath(fileURLToPath(esmEntryPoint)),
+        canonicalPath(fileURLToPath(esmModuleCheck)),
         canonicalPath(path.join(installedPackageRoot, installedPackageJson.exports.import.default)),
-        'ES module consumers should resolve the packaged ES module entry point',
+        'ES module consumers should load the packaged runtime facade',
     );
 } finally {
     fs.rmSync(testRoot, { recursive: true, force: true });
 
@@ -2,11 +2,13 @@ import type {
     PackageManager,
     Pep440Version,
     PythonEnvironment,
+    PythonEnvironmentApi,
     PythonPackageGetterApi,
 } from '@vscode/python-environments';
 import {
     isPackageVersionLookupNotSupportedError,
     PackageVersionLookupNotSupportedError,
+    PythonEnvironments,
 } from '@vscode/python-environments';
 
 type Equal<Left, Right> =
@@ -32,6 +34,7 @@ const explicitLegacyAvailableVersions: Promise<Pep440Version[] | undefined> = ap
 const throwingAvailableVersions: Promise<Pep440Version[]> = api.getPackageAvailableVersions(environment, 'example', {
     errorMode: 'throw',
 });
+const runtimeApi: Promise<PythonEnvironmentApi> = PythonEnvironments.api();
 
 // The unsupported-capability error is part of the public contract: it is constructible, extends
 // Error, and exposes a stable string-literal `code` discriminator.
@@ -50,6 +53,7 @@ void refreshReturnIsExact;
 void legacyAvailableVersions;
 void explicitLegacyAvailableVersions;
 void throwingAvailableVersions;
+void runtimeApi;
 void lookupErrorIsError;
 void lookupErrorCodeIsExact;
 void guardNarrows;