diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7efc47be4df..277f62a51b5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,13 @@ Generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).
 
 
 
+## [17.10.1](https://github.com/netlify/cli/compare/v17.10.0...v17.10.1) (2023-12-08)
+
+
+### Bug Fixes
+
+* use correct file extensions for transpilation ([#6256](https://github.com/netlify/cli/issues/6256)) ([8308097](https://github.com/netlify/cli/commit/8308097334fc76117cee4798772abf18ff5a7e4d))
+
 ## [17.10.0](https://github.com/netlify/cli/compare/v17.9.0...v17.10.0) (2023-12-06)
 
 
diff --git a/package-lock.json b/package-lock.json
index 899c453f3d4..ee3ede96d94 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "netlify-cli",
-  "version": "17.10.0",
+  "version": "17.10.1",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "netlify-cli",
-      "version": "17.10.0",
+      "version": "17.10.1",
       "hasInstallScript": true,
       "license": "MIT",
       "dependencies": {
diff --git a/package.json b/package.json
index e1e18e7ac58..3fbe9eaffe0 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "netlify-cli",
   "description": "Netlify command line tool",
-  "version": "17.10.0",
+  "version": "17.10.1",
   "author": "Netlify Inc.",
   "type": "module",
   "engines": {
diff --git a/src/commands/base-command.ts b/src/commands/base-command.ts
index 7a73b601ddc..91832c5a99a 100644
--- a/src/commands/base-command.ts
+++ b/src/commands/base-command.ts
@@ -38,6 +38,13 @@ import openBrowser from '../utils/open-browser.js'
 import StateConfig from '../utils/state-config.js'
 import { identify, reportError, track } from '../utils/telemetry/index.js'
 
+import { type NetlifyOptions } from './types.js'
+
+type Analytics = {
+  startTime: bigint
+  payload?: Record<string, unknown>
+}
+
 // load the autocomplete plugin
 inquirer.registerPrompt('autocomplete', inquirerAutocompletePrompt)
 /** Netlify CLI client id. Lives in bot@netlify.com */
@@ -61,21 +68,11 @@ const HELP_SEPARATOR_WIDTH = 5
  */
 const COMMANDS_WITHOUT_WORKSPACE_OPTIONS = new Set(['api', 'recipes', 'completion', 'status', 'switch', 'login', 'lm'])
 
-/**
- * Formats a help list correctly with the correct indent
- * @param {string[]} textArray
- * @returns
- */
-// @ts-expect-error TS(7006) FIXME: Parameter 'textArray' implicitly has an 'any' type... Remove this comment to see the full error message
-const formatHelpList = (textArray) => textArray.join('\n').replace(/^/gm, ' '.repeat(HELP_INDENT_WIDTH))
+/** Formats a help list correctly with the correct indent */
+const formatHelpList = (textArray: string[]) => textArray.join('\n').replace(/^/gm, ' '.repeat(HELP_INDENT_WIDTH))
 
-/**
- * Get the duration between a start time and the current time
- * @param {bigint} startTime
- * @returns
- */
-// @ts-expect-error TS(7006) FIXME: Parameter 'startTime' implicitly has an 'any' type... Remove this comment to see the full error message
-const getDuration = function (startTime) {
+/** Get the duration between a start time and the current time */
+const getDuration = (startTime: bigint) => {
   const durationNs = process.hrtime.bigint() - startTime
   return Math.round(Number(durationNs / BigInt(NANO_SECS_TO_MSECS)))
 }
@@ -83,13 +80,8 @@ const getDuration = function (startTime) {
 /**
  * Retrieves a workspace package based of the filter flag that is provided.
  * If the filter flag does not match a workspace package or is not defined then it will prompt with an autocomplete to select a package
- * @param {Project} project
- * @param {string=} filter
- * @returns {Promise<string>}
  */
-// @ts-expect-error TS(7006) FIXME: Parameter 'project' implicitly has an 'any' type.
-async function selectWorkspace(project, filter) {
-  // @ts-expect-error TS(7006) FIXME: Parameter 'pkg' implicitly has an 'any' type.
+async function selectWorkspace(project: Project, filter?: string): Promise<string> {
   const selected = project.workspace?.packages.find((pkg) => {
     if (
       project.relativeBaseDirectory &&
@@ -113,9 +105,7 @@ async function selectWorkspace(project, filter) {
       // @ts-expect-error TS(7006) FIXME: Parameter '_' implicitly has an 'any' type.
       source: (/** @type {string} */ _, input = '') =>
         (project.workspace?.packages || [])
-          // @ts-expect-error TS(7006) FIXME: Parameter 'pkg' implicitly has an 'any' type.
           .filter((pkg) => pkg.path.includes(input))
-          // @ts-expect-error TS(7006) FIXME: Parameter 'pkg' implicitly has an 'any' type.
           .map((pkg) => ({
             name: `${pkg.name ? `${chalk.bold(pkg.name)}  ` : ''}${pkg.path}  ${chalk.dim(
               `--filter ${pkg.name || pkg.path}`,
@@ -138,19 +128,12 @@ async function getRepositoryRoot(cwd?: string): Promise<string | undefined> {
 
 /** Base command class that provides tracking and config initialization */
 export default class BaseCommand extends Command {
-  /**
-   * The netlify object inside each command with the state
-   * @type {import('./types.js').NetlifyOptions}
-   */
-  // @ts-expect-error TS(7008) FIXME: Member 'netlify' implicitly has an 'any' type.
-  netlify
-
-  /** @type {{ startTime: bigint, payload?: any}} */
-  analytics = { startTime: process.hrtime.bigint() }
-
-  /** @type {Project} */
-  // @ts-expect-error TS(7008) FIXME: Member 'project' implicitly has an 'any' type.
-  project
+  /** The netlify object inside each command with the state */
+  // @ts-expect-error This will be set for each command, TypeScript is just not able to infer it
+  netlify: NetlifyOptions
+  analytics: Analytics = { startTime: process.hrtime.bigint() }
+  // @ts-expect-error This will be set for each command, TypeScript is just not able to infer it
+  project: Project
 
   /**
    * The working directory that is used for reading the `netlify.toml` file and storing the state.
@@ -164,25 +147,16 @@ export default class BaseCommand extends Command {
   /**
    * The workspace root if inside a mono repository.
    * Must not be the repository root!
-   * @type {string|undefined}
    */
-  // @ts-expect-error TS(7008) FIXME: Member 'jsWorkspaceRoot' implicitly has an 'any' t... Remove this comment to see the full error message
-  jsWorkspaceRoot
-  /**
-   * The current workspace package we should execute the commands in
-   * @type {string|undefined}
-   */
-  // @ts-expect-error TS(7008) FIXME: Member 'workspacePackage' implicitly has an 'any' ... Remove this comment to see the full error message
-  workspacePackage
+  jsWorkspaceRoot?: string
+  /** The current workspace package we should execute the commands in  */
+  workspacePackage?: string
 
   /**
    * IMPORTANT this function will be called for each command!
    * Don't do anything expensive in there.
-   * @param {string} name The command name
-   * @returns
    */
-  // @ts-expect-error TS(7006) FIXME: Parameter 'name' implicitly has an 'any' type.
-  createCommand(name) {
+  createCommand(name: string): BaseCommand {
     const base = new BaseCommand(name)
       // If  --silent or --json flag passed disable logger
       .addOption(new Option('--json', 'Output return values as JSON').hideHelp(true))
@@ -229,38 +203,28 @@ export default class BaseCommand extends Command {
       }
       debug(`${name}:preAction`)('start')
       this.analytics = { startTime: process.hrtime.bigint() }
-      await this.init(actionCommand)
+      await this.init(actionCommand as BaseCommand)
       debug(`${name}:preAction`)('end')
     })
   }
 
-  /** @private */
-  noBaseOptions = false
-
+  #noBaseOptions = false
   /** don't show help options on command overview (mostly used on top commands like `addons` where options only apply on children) */
   noHelpOptions() {
-    this.noBaseOptions = true
+    this.#noBaseOptions = true
     return this
   }
 
-  /** @type {string[]} The examples list for the command (used inside doc generation and help page) */
-  examples = []
-
-  /**
-   * Set examples for the command
-   * @param {string[]} examples
-   */
-  // @ts-expect-error TS(7006) FIXME: Parameter 'examples' implicitly has an 'any' type.
-  addExamples(examples) {
+  /** The examples list for the command (used inside doc generation and help page) */
+  examples: string[] = []
+  /** Set examples for the command  */
+  addExamples(examples: string[]) {
     this.examples = examples
     return this
   }
 
-  /**
-   * Overrides the help output of commander with custom styling
-   * @returns {import('commander').Help}
-   */
-  createHelp() {
+  /** Overrides the help output of commander with custom styling */
+  createHelp(): Help {
     const help = super.createHelp()
 
     help.commandUsage = (command) => {
@@ -294,13 +258,8 @@ export default class BaseCommand extends Command {
     help.longestSubcommandTermLength = (command: BaseCommand): number =>
       getCommands(command).reduce((max, cmd) => Math.max(max, cmd.name().length), 0)
 
-    /**
-     * override the longestOptionTermLength to react on hide options flag
-     * @param {BaseCommand} command
-     * @param {import('commander').Help} helper
-     * @returns {number}
-     */
-    help.longestOptionTermLength = (command, helper) =>
+    /** override the longestOptionTermLength to react on hide options flag */
+    help.longestOptionTermLength = (command: BaseCommand, helper: Help): number =>
       // @ts-expect-error TS(2551) FIXME: Property 'noBaseOptions' does not exist on type 'C... Remove this comment to see the full error message
       (command.noBaseOptions === false &&
         helper.visibleOptions(command).reduce((max, option) => Math.max(max, helper.optionTerm(option).length), 0)) ||
@@ -310,15 +269,8 @@ export default class BaseCommand extends Command {
       const parentCommand = this.name() === 'netlify' ? command : command.parent
       const termWidth = helper.padWidth(command, helper)
       const helpWidth = helper.helpWidth || FALLBACK_HELP_CMD_WIDTH
-      /**
-       * formats a term correctly
-       * @param {string} term
-       * @param {string} [description]
-       * @param {boolean} [isCommand]
-       * @returns {string}
-       */
-      // @ts-expect-error TS(7006) FIXME: Parameter 'term' implicitly has an 'any' type.
-      const formatItem = (term, description, isCommand = false) => {
+      // formats a term correctly
+      const formatItem = (term: string, description?: string, isCommand = false): string => {
         const bang = isCommand ? `${HELP_$} ` : ''
 
         if (description) {
@@ -330,25 +282,20 @@ export default class BaseCommand extends Command {
         return `${bang}${term}`
       }
 
-      /** @type {string[]} */
-      // @ts-expect-error TS(7034) FIXME: Variable 'output' implicitly has type 'any[]' in s... Remove this comment to see the full error message
-      let output = []
+      let output: string[] = []
 
       // Description
       const [topDescription, ...commandDescription] = (helper.commandDescription(command) || '').split('\n')
       if (topDescription.length !== 0) {
-        // @ts-expect-error TS(7005) FIXME: Variable 'output' implicitly has an 'any[]' type.
         output = [...output, topDescription, '']
       }
 
       // on the parent help command the version should be displayed
       if (this.name() === 'netlify') {
-        // @ts-expect-error TS(7005) FIXME: Variable 'output' implicitly has an 'any[]' type.
         output = [...output, chalk.bold('VERSION'), formatHelpList([formatItem(USER_AGENT)]), '']
       }
 
       // Usage
-      // @ts-expect-error TS(7005) FIXME: Variable 'output' implicitly has an 'any[]' type.
       output = [...output, chalk.bold('USAGE'), helper.commandUsage(command), '']
 
       // Arguments
@@ -359,7 +306,7 @@ export default class BaseCommand extends Command {
         output = [...output, chalk.bold('ARGUMENTS'), formatHelpList(argumentList), '']
       }
 
-      if (command.noBaseOptions === false) {
+      if (command.#noBaseOptions === false) {
         // Options
         const optionList = helper
           .visibleOptions(command)
@@ -405,14 +352,9 @@ export default class BaseCommand extends Command {
     return help
   }
 
-  /**
-   * Will be called on the end of an action to track the metrics
-   * @param {*} [error_]
-   */
-  // @ts-expect-error TS(7006) FIXME: Parameter 'error_' implicitly has an 'any' type.
-  async onEnd(error_) {
-    // @ts-expect-error TS(2339) FIXME: Property 'payload' does not exist on type '{ start... Remove this comment to see the full error message
-    const { payload, startTime } = this.analytics
+  /** Will be called on the end of an action to track the metrics */
+  async onEnd(error_?: unknown) {
+    const { payload = {}, startTime } = this.analytics
     const duration = getDuration(startTime)
     const status = error_ === undefined ? 'success' : 'error'
 
@@ -430,7 +372,6 @@ export default class BaseCommand extends Command {
     } catch {}
 
     if (error_ !== undefined) {
-      // @ts-expect-error TS(2345) FIXME: Argument of type 'string | Error' is not assignabl... Remove this comment to see the full error message
       error(error_ instanceof Error ? error_ : format(error_), { exit: false })
       exit(1)
     }
@@ -504,25 +445,18 @@ export default class BaseCommand extends Command {
     return accessToken
   }
 
-  /**
-   * Adds some data to the analytics payload
-   * @param {Record<string, unknown>} payload
-   */
-  // @ts-expect-error TS(7006) FIXME: Parameter 'payload' implicitly has an 'any' type.
-  setAnalyticsPayload(payload) {
-    // @ts-expect-error TS(2339) FIXME: Property 'payload' does not exist on type '{ start... Remove this comment to see the full error message
-    const newPayload = { ...this.analytics.payload, ...payload }
-    // @ts-expect-error TS(2322) FIXME: Type '{ payload: any; startTime: bigint; }' is not... Remove this comment to see the full error message
-    this.analytics = { ...this.analytics, payload: newPayload }
+  /** Adds some data to the analytics payload */
+  setAnalyticsPayload(payload: Record<string, unknown>) {
+    this.analytics = {
+      ...this.analytics,
+      payload: { ...this.analytics.payload, ...payload },
+    }
   }
 
   /**
    * Initializes the options and parses the configuration needs to be called on start of a command function
-   * @param {BaseCommand} actionCommand The command of the action that is run (`this.` gets the parent command)
-   * @private
    */
-  // @ts-expect-error TS(7006) FIXME: Parameter 'actionCommand' implicitly has an 'any' ... Remove this comment to see the full error message
-  async init(actionCommand) {
+  private async init(actionCommand: BaseCommand) {
     debug(`${actionCommand.name()}:init`)('start')
     const flags = actionCommand.opts()
     // here we actually want to use the process.cwd as we are setting the workingDir
@@ -551,8 +485,7 @@ export default class BaseCommand extends Command {
         })
       })
     const frameworks = await this.project.detectFrameworks()
-    /** @type { string|undefined} */
-    let packageConfig = flags.config ? resolve(flags.config) : undefined
+    let packageConfig: string | undefined = flags.config ? resolve(flags.config) : undefined
     // check if we have detected multiple projects inside which one we have to perform our operations.
     // only ask to select one if on the workspace root
     if (
@@ -577,17 +510,19 @@ export default class BaseCommand extends Command {
     const state = new StateConfig(this.workingDir)
     const [token] = await getToken(flags.auth)
 
-    const apiUrlOpts = {
+    const apiUrlOpts: {
+      userAgent: string
+      scheme?: string
+      host?: string
+      pathPrefix?: string
+    } = {
       userAgent: USER_AGENT,
     }
 
     if (process.env.NETLIFY_API_URL) {
       const apiUrl = new URL(process.env.NETLIFY_API_URL)
-      // @ts-expect-error TS(2339) FIXME: Property 'scheme' does not exist on type '{ userAg... Remove this comment to see the full error message
       apiUrlOpts.scheme = apiUrl.protocol.slice(0, -1)
-      // @ts-expect-error TS(2339) FIXME: Property 'host' does not exist on type '{ userAgen... Remove this comment to see the full error message
       apiUrlOpts.host = apiUrl.host
-      // @ts-expect-error TS(2339) FIXME: Property 'pathPrefix' does not exist on type '{ us... Remove this comment to see the full error message
       apiUrlOpts.pathPrefix =
         process.env.NETLIFY_API_URL === `${apiUrl.protocol}//${apiUrl.host}` ? '/api/v1' : apiUrl.pathname
     }
@@ -613,7 +548,8 @@ export default class BaseCommand extends Command {
       certificateFile: flags.httpProxyCertificateFilename,
     })
     const apiOpts = { ...apiUrlOpts, agent }
-    const api = new NetlifyAPI(token || '', apiOpts)
+    // TODO: remove typecast once we have proper types for the API
+    const api = new NetlifyAPI(token || '', apiOpts) as NetlifyOptions['api']
 
     // If a user passes a site name as an option instead of a site ID to options.site, the siteInfo object
     // will only have the property siteInfo.id. Checking for one of the other properties ensures that we can do
@@ -631,7 +567,6 @@ export default class BaseCommand extends Command {
     // ==================================================
     // Perform analytics reporting
     // ==================================================
-    // @ts-expect-error TS(7006) FIXME: Parameter 'framework' implicitly has an 'any' type... Remove this comment to see the full error message
     const frameworkIDs = frameworks?.map((framework) => framework.id)
     if (frameworkIDs?.length !== 0) {
       this.setAnalyticsPayload({ frameworks: frameworkIDs })
@@ -639,7 +574,6 @@ export default class BaseCommand extends Command {
     this.setAnalyticsPayload({
       monorepo: Boolean(this.project.workspace),
       packageManager: this.project.packageManager?.name,
-      // @ts-expect-error TS(7031) FIXME: Binding element 'id' implicitly has an 'any' type.
       buildSystem: this.project.buildSystems.map(({ id }) => id),
     })
 
@@ -687,23 +621,21 @@ export default class BaseCommand extends Command {
     debug(`${this.name()}:init`)('end')
   }
 
-  /**
-   * Find and resolve the Netlify configuration
-   * @param {object} config
-   * @param {string} config.cwd
-   * @param {string|null=} config.token
-   * @param {*} config.state
-   * @param {boolean=} config.offline
-   * @param {string=} config.configFilePath An optional path to the netlify configuration file e.g. netlify.toml
-   * @param {string=} config.packagePath
-   * @param {string=} config.repositoryRoot
-   * @param {string=} config.host
-   * @param {string=} config.pathPrefix
-   * @param {string=} config.scheme
-   * @returns {ReturnType<typeof resolveConfig>}
-   */
-  // @ts-expect-error TS(7023) FIXME: 'getConfig' implicitly has return type 'any' becau... Remove this comment to see the full error message
-  async getConfig(config) {
+  /** Find and resolve the Netlify configuration */
+  async getConfig(config: {
+    cwd: string
+    token?: string | null
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    state?: any
+    offline?: boolean
+    /** An optional path to the netlify configuration file e.g. netlify.toml */
+    configFilePath?: string
+    packagePath?: string
+    repositoryRoot?: string
+    host?: string
+    pathPrefix?: string
+    scheme?: string
+  }): ReturnType<typeof resolveConfig> {
     // the flags that are passed to the command like `--debug` or `--offline`
     const flags = this.opts()
 
@@ -754,10 +686,15 @@ export default class BaseCommand extends Command {
    * Returns the context that should be used in case one hasn't been explicitly
    * set. The default context is `dev` most of the time, but some commands may
    * wish to override that.
-   *
-   * @returns {'production' | 'dev'}
    */
-  getDefaultContext() {
+  getDefaultContext(): 'production' | 'dev' {
     return this.name() === 'serve' ? 'production' : 'dev'
   }
+
+  /**
+   * Retrieve feature flags for this site
+   */
+  getFeatureFlag<T = null | boolean | string>(flagName: string): T {
+    return this.netlify.siteInfo.feature_flags?.[flagName] || null
+  }
 }
diff --git a/src/commands/dev/dev.ts b/src/commands/dev/dev.ts
index 62eda3e7a43..50f1da5a745 100644
--- a/src/commands/dev/dev.ts
+++ b/src/commands/dev/dev.ts
@@ -29,6 +29,7 @@ import { getGeoCountryArgParser } from '../../utils/validation.js'
 import BaseCommand from '../base-command.js'
 
 import { createDevExecCommand } from './dev-exec.js'
+import { type DevConfig } from './types.js'
 
 /**
  *
@@ -90,7 +91,6 @@ export const dev = async (options: OptionValues, command: BaseCommand) => {
   const { api, cachedConfig, config, repositoryRoot, site, siteInfo, state } = command.netlify
   config.dev = { ...config.dev }
   config.build = { ...config.build }
-  /** @type {import('./types.js').DevConfig} */
   const devConfig = {
     framework: '#auto',
     autoLaunch: Boolean(options.open),
@@ -99,7 +99,7 @@ export const dev = async (options: OptionValues, command: BaseCommand) => {
     ...(config.build.base && { base: config.build.base }),
     ...config.dev,
     ...options,
-  }
+  } as DevConfig
 
   let { env } = cachedConfig
 
diff --git a/src/commands/link/link.ts b/src/commands/link/link.ts
index cce6a46a7bb..30889cb2525 100644
--- a/src/commands/link/link.ts
+++ b/src/commands/link/link.ts
@@ -211,7 +211,6 @@ or run ${chalk.cyanBright('netlify sites:create')} to create a site.`)
       } catch (error_) {
         // @ts-expect-error TS(2571) FIXME: Object is of type 'unknown'.
         if (error_.status === 404) {
-          // @ts-expect-error TS(2345) FIXME: Argument of type 'Error' is not assignable to para... Remove this comment to see the full error message
           error(new Error(`Site ID '${siteId}' not found`))
         } else {
           // @ts-expect-error TS(2345) FIXME: Argument of type 'unknown' is not assignable to pa... Remove this comment to see the full error message
@@ -225,7 +224,6 @@ or run ${chalk.cyanBright('netlify sites:create')} to create a site.`)
   }
 
   if (!site) {
-    // @ts-expect-error TS(2345) FIXME: Argument of type 'Error' is not assignable to para... Remove this comment to see the full error message
     error(new Error(`No site found`))
   }
 
@@ -285,7 +283,6 @@ export const link = async (options: OptionValues, command: BaseCommand) => {
     } catch (error_) {
       // @ts-expect-error TS(2571) FIXME: Object is of type 'unknown'.
       if (error_.status === 404) {
-        // @ts-expect-error TS(2345) FIXME: Argument of type 'Error' is not assignable to para... Remove this comment to see the full error message
         error(new Error(`Site id ${options.id} not found`))
       } else {
         // @ts-expect-error TS(2345) FIXME: Argument of type 'unknown' is not assignable to pa... Remove this comment to see the full error message
@@ -315,7 +312,6 @@ export const link = async (options: OptionValues, command: BaseCommand) => {
     } catch (error_) {
       // @ts-expect-error TS(2571) FIXME: Object is of type 'unknown'.
       if (error_.status === 404) {
-        // @ts-expect-error TS(2345) FIXME: Argument of type 'Error' is not assignable to para... Remove this comment to see the full error message
         error(new Error(`${options.name} not found`))
       } else {
         // @ts-expect-error TS(2345) FIXME: Argument of type 'unknown' is not assignable to pa... Remove this comment to see the full error message
@@ -324,7 +320,6 @@ export const link = async (options: OptionValues, command: BaseCommand) => {
     }
 
     if (results.length === 0) {
-      // @ts-expect-error TS(2345) FIXME: Argument of type 'Error' is not assignable to para... Remove this comment to see the full error message
       error(new Error(`No sites found named ${options.name}`))
     }
     const [firstSiteData] = results
diff --git a/src/commands/serve/serve.ts b/src/commands/serve/serve.ts
index 762ab246662..d136d55c4bf 100644
--- a/src/commands/serve/serve.ts
+++ b/src/commands/serve/serve.ts
@@ -25,12 +25,12 @@ import { generateInspectSettings, startProxyServer } from '../../utils/proxy-ser
 import { runBuildTimeline } from '../../utils/run-build.js'
 import type { ServerSettings } from '../../utils/types.js'
 import BaseCommand from '../base-command.js'
+import { type DevConfig } from '../dev/types.js'
 
 export const serve = async (options: OptionValues, command: BaseCommand) => {
   const { api, cachedConfig, config, repositoryRoot, site, siteInfo, state } = command.netlify
   config.dev = { ...config.dev }
   config.build = { ...config.build }
-  /** @type {import('../dev/types').DevConfig} */
   const devConfig = {
     ...(config.functionsDirectory && { functions: config.functionsDirectory }),
     ...(config.build.publish && { publish: config.build.publish }),
@@ -40,7 +40,7 @@ export const serve = async (options: OptionValues, command: BaseCommand) => {
     // Override the `framework` value so that we start a static server and not
     // the framework's development server.
     framework: '#static',
-  }
+  } as DevConfig
 
   let { env } = cachedConfig
 
diff --git a/src/commands/types.d.ts b/src/commands/types.d.ts
index dcb4c643b85..f776e22570e 100644
--- a/src/commands/types.d.ts
+++ b/src/commands/types.d.ts
@@ -3,6 +3,9 @@ import type { NetlifyAPI } from 'netlify'
 
 import StateConfig from '../utils/state-config.js'
 
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+type $TSFixMe = any;
+
 export type NetlifySite = {
   root?: string
   configPath?: string
@@ -11,21 +14,32 @@ export type NetlifySite = {
   set id(id: string): void
 }
 
+type PatchedConfig = NetlifyTOML & {
+  functionsDirectory?: string
+  build: NetlifyTOML['build'] & {
+    functionsSource?: string
+  }
+  dev: NetlifyTOML['dev'] & {
+    functions?: string
+  }
+}
+
 /**
  * The netlify object inside each command with the state
  */
 export type NetlifyOptions = {
-  api: NetlifyAPI
-  apiOpts: unknown
+  // poorly duck type the missing api functions
+  api: NetlifyAPI & Record<string, (...args: $TSFixMe) => Promise<$TSFixMe>>
+  apiOpts: $TSFixMe
   repositoryRoot: string
   /** Absolute path of the netlify configuration file */
   configFilePath: string
   /** Relative path of the netlify configuration file */
   relConfigFilePath: string
   site: NetlifySite
-  siteInfo: unknown
-  config: NetlifyTOML
-  cachedConfig: Record<string, unknown>
-  globalConfig: unknown
+  siteInfo: $TSFixMe
+  config: PatchedConfig
+  cachedConfig: Record<string, $TSFixMe>
+  globalConfig: $TSFixMe
   state: StateConfig
 }
diff --git a/src/lib/functions/netlify-function.ts b/src/lib/functions/netlify-function.ts
index 8acd316709c..f4f55501771 100644
--- a/src/lib/functions/netlify-function.ts
+++ b/src/lib/functions/netlify-function.ts
@@ -121,7 +121,7 @@ export default class NetlifyFunction {
     }
 
     if (extension === '.js') {
-      return '.js'
+      return '.mjs'
     }
   }
 
diff --git a/src/lib/functions/runtimes/js/builders/zisi.ts b/src/lib/functions/runtimes/js/builders/zisi.ts
index e85de6f0429..1d08ab35112 100644
--- a/src/lib/functions/runtimes/js/builders/zisi.ts
+++ b/src/lib/functions/runtimes/js/builders/zisi.ts
@@ -175,7 +175,7 @@ export default async function handler({ config, directory, errorExit, func, meta
     featureFlags.zisi_pure_esm_mjs = true
   } else {
     // We must use esbuild for certain file extensions.
-    const mustTranspile = ['.js', '.ts', '.mts', '.cts'].includes(path.extname(func.mainFile))
+    const mustTranspile = ['.mjs', '.ts', '.mts', '.cts'].includes(path.extname(func.mainFile))
     const mustUseEsbuild = hasTypeModule || mustTranspile
 
     if (mustUseEsbuild && !functionsConfig['*'].nodeBundler) {
diff --git a/src/utils/command-helpers.ts b/src/utils/command-helpers.ts
index ee53421d7f8..5c884e28b51 100644
--- a/src/utils/command-helpers.ts
+++ b/src/utils/command-helpers.ts
@@ -184,23 +184,16 @@ export const warn = (message = '') => {
   log(` ${bang}   Warning: ${message}`)
 }
 
-/**
- * throws an error or log it
- * @param {unknown} message
- * @param {object} [options]
- * @param {boolean} [options.exit]
- */
-export const error = (message = '', options = {}) => {
+/** Throws an error or logs it */
+export const error = (message: Error | string = '', options: { exit?: boolean } = {}) => {
   const err =
-    // @ts-expect-error TS(2358) FIXME: The left-hand side of an 'instanceof' expression m... Remove this comment to see the full error message
     message instanceof Error
       ? message
       : // eslint-disable-next-line unicorn/no-nested-ternary
       typeof message === 'string'
       ? new Error(message)
-      : /** @type {Error} */ { message, stack: undefined, name: 'Error' }
+      : { message, stack: undefined, name: 'Error' }
 
-  // @ts-expect-error TS(2339) FIXME: Property 'exit' does not exist on type '{}'.
   if (options.exit === false) {
     const bang = chalk.red(BANG)
     if (process.env.DEBUG) {
diff --git a/src/utils/detect-server-settings.ts b/src/utils/detect-server-settings.ts
index 18bc5a1904e..5fe75bea9cb 100644
--- a/src/utils/detect-server-settings.ts
+++ b/src/utils/detect-server-settings.ts
@@ -2,14 +2,19 @@ import { readFile } from 'fs/promises'
 import { EOL } from 'os'
 import { dirname, relative, resolve } from 'path'
 
-import { getFramework, getSettings } from '@netlify/build-info'
+import { Project, Settings, getFramework, getSettings } from '@netlify/build-info'
+import type { OptionValues } from 'commander'
 import getPort from 'get-port'
 
+import BaseCommand from '../commands/base-command.js'
+import { type DevConfig } from '../commands/dev/types.js'
+
 import { detectFrameworkSettings } from './build-info.js'
 import { NETLIFYDEVWARN, chalk, log } from './command-helpers.js'
 import { acquirePort } from './dev.js'
 import { getInternalFunctionsDir } from './functions/functions.js'
 import { getPluginsToAutoInstall } from './init/utils.js'
+import { BaseServerSettings, ServerSettings } from './types.js'
 
 /** @param {string} str */
 // @ts-expect-error TS(7006) FIXME: Parameter 'str' implicitly has an 'any' type.
@@ -180,11 +185,8 @@ const handleStaticServer = async ({ devConfig, flags, workingDir }) => {
 
 /**
  * Retrieves the settings from a framework
- * @param {import('@netlify/build-info').Settings} [settings]
- * @returns {import('./types.js').BaseServerSettings | undefined}
  */
-// @ts-expect-error TS(7006) FIXME: Parameter 'settings' implicitly has an 'any' type.
-const getSettingsFromDetectedSettings = (settings) => {
+const getSettingsFromDetectedSettings = (command: BaseCommand, settings?: Settings) => {
   if (!settings) {
     return
   }
@@ -196,7 +198,7 @@ const getSettingsFromDetectedSettings = (settings) => {
     framework: settings.framework.name,
     env: settings.env,
     pollingStrategies: settings.pollingStrategies,
-    plugins: getPluginsToAutoInstall(settings.plugins_from_config_file, settings.plugins_recommended),
+    plugins: getPluginsToAutoInstall(command, settings.plugins_from_config_file, settings.plugins_recommended),
   }
 }
 
@@ -265,32 +267,29 @@ const mergeSettings = async ({ devConfig, frameworkSettings = {}, workingDir })
 
 /**
  * Handles a forced framework and retrieves the settings for it
- * @param {object} config
- * @param {import('../commands/dev/types.js').DevConfig} config.devConfig
- * @param {import('@netlify/build-info').Project} config.project
- * @param {string} config.workingDir
- * @param {string=} config.workspacePackage
- * @returns {Promise<import('./types.js').BaseServerSettings>}
  */
-// @ts-expect-error TS(7031) FIXME: Binding element 'devConfig' implicitly has an 'any... Remove this comment to see the full error message
-const handleForcedFramework = async ({ devConfig, project, workingDir, workspacePackage }) => {
+const handleForcedFramework = async (options: {
+  command: BaseCommand
+  devConfig: DevConfig
+  project: Project
+  workingDir: string
+  workspacePackage?: string
+}): Promise<BaseServerSettings> => {
   // this throws if `devConfig.framework` is not a supported framework
-  const framework = await getFramework(devConfig.framework, project)
-  const settings = await getSettings(framework, project, workspacePackage || '')
-  const frameworkSettings = getSettingsFromDetectedSettings(settings)
-  return mergeSettings({ devConfig, workingDir, frameworkSettings })
+  const framework = await getFramework(options.devConfig.framework, options.project)
+  const settings = await getSettings(framework, options.project, options.workspacePackage || '')
+  const frameworkSettings = getSettingsFromDetectedSettings(options.command, settings)
+  return mergeSettings({ devConfig: options.devConfig, workingDir: options.workingDir, frameworkSettings })
 }
 
 /**
  * Get the server settings based on the flags and the devConfig
- * @param {import('../commands/dev/types.js').DevConfig} devConfig
- * @param {import('commander').OptionValues} flags
- * @param {import('../commands/base-command.js').default} command
- * @returns {Promise<import('./types.js').ServerSettings>}
  */
-
-// @ts-expect-error TS(7006) FIXME: Parameter 'devConfig' implicitly has an 'any' type... Remove this comment to see the full error message
-const detectServerSettings = async (devConfig, flags, command) => {
+const detectServerSettings = async (
+  devConfig: DevConfig,
+  flags: OptionValues,
+  command: BaseCommand,
+): Promise<ServerSettings> => {
   validateProperty(devConfig, 'framework', 'string')
 
   /** @type {Partial<import('./types.js').BaseServerSettings>} */
@@ -304,7 +303,7 @@ const detectServerSettings = async (devConfig, flags, command) => {
 
     const runDetection = !hasCommandAndTargetPort(devConfig)
     const frameworkSettings = runDetection
-      ? getSettingsFromDetectedSettings(await detectFrameworkSettings(command, 'dev'))
+      ? getSettingsFromDetectedSettings(command, await detectFrameworkSettings(command, 'dev'))
       : undefined
     if (frameworkSettings === undefined && runDetection) {
       log(`${NETLIFYDEVWARN} No app server detected. Using simple static server`)
@@ -325,6 +324,7 @@ const detectServerSettings = async (devConfig, flags, command) => {
     validateFrameworkConfig({ devConfig })
     // this is when the user explicitly configures a framework, e.g. `framework = "gatsby"`
     settings = await handleForcedFramework({
+      command,
       devConfig,
       project: command.project,
       workingDir: command.workingDir,
diff --git a/src/utils/init/utils.ts b/src/utils/init/utils.ts
index 0e8bfb3f1f0..f349693f0d6 100644
--- a/src/utils/init/utils.ts
+++ b/src/utils/init/utils.ts
@@ -1,9 +1,12 @@
 import { writeFile } from 'fs/promises'
 import path from 'path'
 
+import { NetlifyConfig } from '@netlify/build'
+import { Settings } from '@netlify/build-info'
 import cleanDeep from 'clean-deep'
 import inquirer from 'inquirer'
 
+import BaseCommand from '../../commands/base-command.js'
 import { fileExistsAsync } from '../../lib/fs.js'
 import { normalizeBackslash } from '../../lib/path.js'
 import { detectBuildSettings } from '../build-info.js'
@@ -11,43 +14,44 @@ import { chalk, error as failAndExit, log, warn } from '../command-helpers.js'
 
 import { getRecommendPlugins, getUIPlugins } from './plugins.js'
 
-// these plugins represent runtimes that are
-// expected to be "automatically" installed. Even though
-// they can be installed on package/toml, we always
-// want them installed in the site settings. When installed
-// there our build will automatically install the latest without
-// user management of the versioning.
-const pluginsToAlwaysInstall = new Set(['@netlify/plugin-nextjs'])
+const formatTitle = (title: string) => chalk.cyan(title)
 
 /**
  * Retrieve a list of plugins to auto install
- * @param {string[]=} pluginsInstalled
- * @param {string[]=} pluginsRecommended
+ * @param pluginsToAlwaysInstall these plugins represent runtimes that are
+ * expected to be "automatically" installed. Even though
+ * they can be installed on package/toml, we always
+ * want them installed in the site settings. When installed
+ * there our build will automatically install the latest without
+ * user management of the versioning.
+ * @param pluginsInstalled
+ * @param pluginsRecommended
  * @returns
  */
-export const getPluginsToAutoInstall = (pluginsInstalled = [], pluginsRecommended = []) =>
-  pluginsRecommended.reduce(
+export const getPluginsToAutoInstall = (
+  command: BaseCommand,
+  pluginsInstalled: string[] = [],
+  pluginsRecommended: string[] = [],
+) => {
+  const nextRuntime = '@netlify/plugin-nextjs'
+  const pluginsToAlwaysInstall = new Set([nextRuntime])
+  return pluginsRecommended.reduce(
     (acc, plugin) =>
       pluginsInstalled.includes(plugin) && !pluginsToAlwaysInstall.has(plugin) ? acc : [...acc, plugin],
-
-    /** @type {string[]} */ [],
+    [] as string[],
   )
-
+}
 /**
- *
- * @param {Partial<import('@netlify/build-info').Settings>} settings
- * @param {*} config
- * @param {import('../../commands/base-command.js').default} command
  */
-// @ts-expect-error TS(7006) FIXME: Parameter 'settings' implicitly has an 'any' type.
-const normalizeSettings = (settings, config, command) => {
-  const plugins = getPluginsToAutoInstall(settings.plugins_from_config_file, settings.plugins_recommended)
+const normalizeSettings = (settings: Settings, config: NetlifyConfig, command: BaseCommand) => {
+  const plugins = getPluginsToAutoInstall(command, settings.plugins_from_config_file, settings.plugins_recommended)
   const recommendedPlugins = getRecommendPlugins(plugins, config)
 
   return {
     defaultBaseDir: settings.baseDirectory ?? command.project.relativeBaseDirectory ?? '',
     defaultBuildCmd: config.build.command || settings.buildCommand,
     defaultBuildDir: settings.dist,
+    // @ts-expect-error types need to be fixed on @netlify/build
     defaultFunctionsDir: config.build.functions || 'netlify/functions',
     recommendedPlugins,
   }
@@ -106,7 +110,7 @@ export const getBuildSettings = async ({ command, config }) => {
     await normalizeSettings(setting, config, command)
 
   if (recommendedPlugins.length !== 0 && setting.framework?.name) {
-    log(`Configuring ${formatTitle(setting.framework?.name)} runtime...`)
+    log(`Configuring ${formatTitle(setting.framework.name)} runtime...`)
     log()
   }
 
@@ -210,12 +214,6 @@ export const formatErrorMessage = ({ error, message }) => {
   return `${message} with error: ${chalk.red(errorMessage)}`
 }
 
-/**
- * @param {string} title
- */
-// @ts-expect-error TS(7006) FIXME: Parameter 'title' implicitly has an 'any' type.
-const formatTitle = (title) => chalk.cyan(title)
-
 // @ts-expect-error TS(7031) FIXME: Binding element 'api' implicitly has an 'any' type... Remove this comment to see the full error message
 export const createDeployKey = async ({ api }) => {
   try {
diff --git a/tests/integration/commands/deploy/deploy.test.js b/tests/integration/commands/deploy/deploy.test.js
index 4460d6eef80..0bdfbd110c4 100644
--- a/tests/integration/commands/deploy/deploy.test.js
+++ b/tests/integration/commands/deploy/deploy.test.js
@@ -495,7 +495,7 @@ describe.skipIf(process.env.NETLIFY_TEST_DISABLE_LIVE === 'true').concurrent('co
           export default async () => new Response("Internal V2 API")
           export const config = { path: "/internal-v2-func" }
           `,
-          path: '.netlify/functions-internal/func-4.js',
+          path: '.netlify/functions-internal/func-4.mjs',
         })
         .buildAsync()
 
diff --git a/tests/integration/commands/functions-with-args/functions-with-args.test.js b/tests/integration/commands/functions-with-args/functions-with-args.test.js
index bb63fd0e1ee..181c89b459e 100644
--- a/tests/integration/commands/functions-with-args/functions-with-args.test.js
+++ b/tests/integration/commands/functions-with-args/functions-with-args.test.js
@@ -597,7 +597,7 @@ exports.handler = async () => ({
     })
   })
 
-  test('Serves functions with a `.js` extension', async (t) => {
+  test('Serves functions with a `.mjs` extension', async (t) => {
     await withSiteBuilder('function-mjs', async (builder) => {
       const bundlerConfig = args.includes('esbuild') ? { node_bundler: 'esbuild' } : {}
 
@@ -610,7 +610,7 @@ exports.handler = async () => ({
           },
         })
         .withContentFile({
-          path: 'functions/hello.js',
+          path: 'functions/hello.mjs',
           content: `
   const handler = async () => {
     return {
diff --git a/tests/integration/frameworks/hugo.test.ts b/tests/integration/frameworks/hugo.test.ts
index 9990ea3060b..61ec0d9dec7 100644
--- a/tests/integration/frameworks/hugo.test.ts
+++ b/tests/integration/frameworks/hugo.test.ts
@@ -1,11 +1,11 @@
 import { expect, test } from 'vitest'
 
 import { FixtureTestContext, setupFixtureTests } from '../utils/fixture.js'
-import got from '../utils/got.js'
+import fetch from 'node-fetch'
 
 setupFixtureTests('hugo-site', { devServer: true }, () => {
   test<FixtureTestContext>('should not infinite redirect when -d flag is passed', async ({ devServer: { url } }) => {
-    const response = await got(`${url}/`).text()
+    const response = await fetch(`${url}/`).then((res) => res.text())
 
     expect(response).toContain('Home page!')
   })