diff --git a/e2e/harmony/tsconfig-env-mismatch.e2e.ts b/e2e/harmony/tsconfig-env-mismatch.e2e.ts
index b87c34566c61..1f423578c288 100644
--- a/e2e/harmony/tsconfig-env-mismatch.e2e.ts
+++ b/e2e/harmony/tsconfig-env-mismatch.e2e.ts
@@ -41,7 +41,9 @@ describe('tsconfig env mismatch between check-types and build', function () {
     before(() => {
       helper.scopeHelper.setWorkspaceWithRemoteScope();
 
-      // Create permissive tsconfig (no strict mode)
+      // Create permissive tsconfig (strict mode explicitly off).
+      // Setting strict explicitly makes the fixture's intent self-documenting and
+      // independent of any future change to TypeScript's tsconfig defaults.
       const permissiveTsconfig = JSON.stringify(
         {
           compilerOptions: {
@@ -55,7 +57,7 @@ describe('tsconfig env mismatch between check-types and build', function () {
             moduleResolution: 'node',
             esModuleInterop: true,
             outDir: './dist',
-            // No strict mode - permissive
+            strict: false,
           },
           exclude: ['artifacts', 'public', 'dist', 'node_modules'],
         },
diff --git a/scopes/typescript/ts-server/ts-server-client.ts b/scopes/typescript/ts-server/ts-server-client.ts
index 39540640f476..80874253dd96 100644
--- a/scopes/typescript/ts-server/ts-server-client.ts
+++ b/scopes/typescript/ts-server/ts-server-client.ts
@@ -66,14 +66,17 @@ export class TsserverClient {
         onEvent: this.onTsserverEvent.bind(this),
       });
 
-      this.tsServer
-        .start()
-        .then(() => {
-          this.serverRunning = true;
-        })
-        .catch((err) => {
-          this.logger.error('TsserverClient.init failed', err);
-        });
+      // Await the server to be ready before issuing any requests, so a start() failure
+      // (e.g., tsserver writing to stderr) surfaces here rather than producing a write to a
+      // broken stdin, and so the inferred-project options below are applied to a live server.
+      await this.tsServer.start();
+      this.serverRunning = true;
+
+      // TS 6 flipped the `strict` default from false to true for inferred projects.
+      // Files outside any tsconfig (e.g., components whose env's tsconfig isn't included
+      // by the workspace config writer) would otherwise get strict-mode errors that didn't
+      // surface in TS 5. Pin inferred-project options to the TS 5 default to preserve behavior.
+      await this.setCompilerOptionsForInferredProjects({ strict: false });
 
       const shouldOpenFiles = this.options.openFilesOnInit !== false;
       if (this.files.length && shouldOpenFiles) {
@@ -296,6 +299,12 @@ export class TsserverClient {
     return this.tsServer?.request(CommandTypes.Configure, configureArgs);
   }
 
+  private async setCompilerOptionsForInferredProjects(
+    options: ts.server.protocol.ExternalProjectCompilerOptions
+  ): Promise<void> {
+    await this.tsServer?.request(CommandTypes.CompilerOptionsForInferredProjects, { options });
+  }
+
   /**
    * ask tsserver to open a file if it was not opened before.
    * @param file absolute path of the file
diff --git a/scopes/typescript/typescript/typescript.main.runtime.ts b/scopes/typescript/typescript/typescript.main.runtime.ts
index 3146deedf61e..14e91e88ea91 100644
--- a/scopes/typescript/typescript/typescript.main.runtime.ts
+++ b/scopes/typescript/typescript/typescript.main.runtime.ts
@@ -130,6 +130,28 @@ export class TypescriptMain {
     const configMutator = new TypescriptConfigMutator(options);
     const transformerContext: TsConfigTransformContext = {};
     const afterMutation = runTransformersWithContext(configMutator.clone(), transformers, transformerContext);
+    // TS 6 flipped several defaults and turned legacy options into hard errors.
+    // Shipped env tsconfigs must stay valid for TS 5.x consumers, so patch the raw tsconfig
+    // at runtime when the loaded compiler is actually TS 6+ — preserving TS 5 behavior.
+    const tsMajor = parseInt(tsModule.version?.split('.')[0] || '0', 10);
+    const tsconfig = afterMutation.raw.tsconfig;
+    const compilerOptions = tsconfig?.compilerOptions;
+    if (tsMajor >= 6 && compilerOptions) {
+      if (!compilerOptions.ignoreDeprecations) compilerOptions.ignoreDeprecations = '6.0';
+      if (compilerOptions.noUncheckedSideEffectImports === undefined)
+        compilerOptions.noUncheckedSideEffectImports = false;
+      // strict and types: don't inject when the tsconfig extends a base — the base may
+      // already set these, and an explicit value here would silently override the inherited one.
+      if (!tsconfig.extends) {
+        if (compilerOptions.strict === undefined) compilerOptions.strict = false;
+        // TS 6 stopped auto-discovering @types/* packages (types defaults to []).
+        // Seed the types every Bit env installs — @types/node universally and @types/jest
+        // (provides describe/it/expect globals). Don't seed 'mocha': the React env
+        // removes @types/mocha via the `-` convention (see react.env.ts), so seeding it
+        // would make tsc fail to resolve a type package that isn't installed.
+        if (compilerOptions.types === undefined) compilerOptions.types = ['node', 'jest'];
+      }
+    }
     const afterMutationWithoutTsconfig = { ...afterMutation.raw, tsconfig: '' };
 
     return new TypescriptCompiler(
diff --git a/tsconfig.json b/tsconfig.json
index bca37334c636..26c1125bff5a 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -6,6 +6,9 @@
     "strict": true,
     "moduleResolution": "node",
     "module": "commonjs",
+    "ignoreDeprecations": "6.0",
+    "noUncheckedSideEffectImports": false,
+    "types": ["node", "mocha", "chai", "jest"],
     "target": "es2015",
     "skipLibCheck": true,
     "noImplicitAny": false,
diff --git a/workspace.jsonc b/workspace.jsonc
index a4e4228cad4a..c4a39797ab62 100644
--- a/workspace.jsonc
+++ b/workspace.jsonc
@@ -397,6 +397,7 @@
         "@types/lodash.flatten": "4.4.6",
         "@types/lodash.head": "4.0.6",
         "@types/mdx-js__react": "1.5.5",
+        "@types/jest": "29.5.14",
         "@types/memoizee": "0.4.5",
         "@types/mime": "2.0.3",
         "@types/mini-css-extract-plugin": "2.2.0",
@@ -642,7 +643,7 @@
         "tippy.js": "6.2.7",
         "ts-graphviz": "^2.1.6",
         "type-coverage": "2.15.1",
-        "typescript": "5.9.2",
+        "typescript": "6.0.3",
         "ua-parser-js": "0.7.40",
         "uid-number": "0.0.6",
         "uniqid": "5.3.0",
@@ -834,7 +835,7 @@
             "buffer": "6.0.3",
             "process": "0.11.10",
             "react-router-dom": "6.3.0",
-            "typescript": "5.9.2",
+            "typescript": "6.0.3",
             // @parcel/css, lightningcss, @swc/css are used by css-minimizer-webpack-plugin
             // see this issue https://github.com/webpack-contrib/css-minimizer-webpack-plugin/issues/244
             "@parcel/css": "^1.8.3",