diff --git a/packages/cli/src/commands/deploy.ts b/packages/cli/src/commands/deploy.ts
index 166209a3..7a229b4d 100644
--- a/packages/cli/src/commands/deploy.ts
+++ b/packages/cli/src/commands/deploy.ts
@@ -6,7 +6,6 @@ import { Flags, ux } from '@oclif/core'
 import { AuthCommand } from './authCommand'
 import { parseProject } from '../services/project-parser'
 import { loadChecklyConfig } from '../services/checkly-config-loader'
-import { runtimes } from '../rest/api'
 import type { Runtime } from '../rest/runtimes'
 import {
   Check, AlertChannelSubscription, AlertChannel, CheckGroup, Dashboard,
@@ -92,7 +91,8 @@ export default class Deploy extends AuthCommand {
       config: checklyConfig,
       constructs: checklyConfigConstructs,
     } = await loadChecklyConfig(configDirectory, configFilenames)
-    const { data: avilableRuntimes } = await runtimes.getAll()
+    const { data: account } = await api.accounts.get(config.getAccountId())
+    const { data: avilableRuntimes } = await api.runtimes.getAll()
     const project = await parseProject({
       directory: configDirectory,
       projectLogicalId: checklyConfig.logicalId,
@@ -108,6 +108,7 @@ export default class Deploy extends AuthCommand {
         acc[runtime.name] = runtime
         return acc
       }, <Record<string, Runtime>> {}),
+      defaultRuntimeId: account.runtimeId,
       verifyRuntimeDependencies,
       checklyConfigConstructs,
     })
@@ -140,8 +141,6 @@ export default class Deploy extends AuthCommand {
       return
     }
 
-    const { data: account } = await api.accounts.get(config.getAccountId())
-
     if (!force && !preview) {
       const { confirm } = await prompts({
         name: 'confirm',
diff --git a/packages/cli/src/commands/test.ts b/packages/cli/src/commands/test.ts
index f6405373..087f9a36 100644
--- a/packages/cli/src/commands/test.ts
+++ b/packages/cli/src/commands/test.ts
@@ -159,6 +159,7 @@ export default class Test extends AuthCommand {
     })
     const verbose = this.prepareVerboseFlag(verboseFlag, checklyConfig.cli?.verbose)
     const reporterTypes = this.prepareReportersTypes(reporterFlag as ReporterType, checklyConfig.cli?.reporters)
+    const { data: account } = await api.accounts.get(config.getAccountId())
     const { data: availableRuntimes } = await api.runtimes.getAll()
 
     const project = await parseProject({
@@ -176,6 +177,7 @@ export default class Test extends AuthCommand {
         acc[runtime.name] = runtime
         return acc
       }, <Record<string, Runtime>> {}),
+      defaultRuntimeId: account.runtimeId,
       verifyRuntimeDependencies,
       checklyConfigConstructs,
     })
diff --git a/packages/cli/src/constructs/__tests__/api-check.spec.ts b/packages/cli/src/constructs/__tests__/api-check.spec.ts
index 487db3e4..b32136f2 100644
--- a/packages/cli/src/constructs/__tests__/api-check.spec.ts
+++ b/packages/cli/src/constructs/__tests__/api-check.spec.ts
@@ -36,6 +36,84 @@ describe('ApiCheck', () => {
     })
   })
 
+  it('should fail to bundle if runtime is not specified and default runtime is not set', () => {
+    const getFilePath = (filename: string) => path.join(__dirname, 'fixtures', 'api-check', filename)
+    const bundle = () => {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      const _bundle = ApiCheck.bundle(getFilePath('entrypoint.js'), undefined)
+    }
+
+    Session.basePath = __dirname
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = undefined
+    expect(bundle).toThrowError('runtime is not set')
+    delete Session.basePath
+    delete Session.defaultRuntimeId
+  })
+
+  it('should successfully bundle if runtime is not specified but default runtime is set', () => {
+    const getFilePath = (filename: string) => path.join(__dirname, 'fixtures', 'api-check', filename)
+    const bundle = () => {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      const _bundle = ApiCheck.bundle(getFilePath('entrypoint.js'), undefined)
+    }
+
+    Session.basePath = __dirname
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = '2022.10'
+    expect(bundle).not.toThrowError('is not supported')
+    delete Session.basePath
+    delete Session.defaultRuntimeId
+  })
+
+  it('should fail to bundle if runtime is not supported even if default runtime is set', () => {
+    const getFilePath = (filename: string) => path.join(__dirname, 'fixtures', 'api-check', filename)
+    const bundle = () => {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      const _bundle = ApiCheck.bundle(getFilePath('entrypoint.js'), '9999.99')
+    }
+
+    Session.basePath = __dirname
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = '2022.02'
+    expect(bundle).toThrowError('9999.99 is not supported')
+    delete Session.basePath
+    delete Session.defaultRuntimeId
+  })
+
+  it('should not synthesize runtime if not specified even if default runtime is set', () => {
+    Session.project = new Project('project-id', {
+      name: 'Test Project',
+      repoUrl: 'https://github.com/checkly/checkly-cli',
+    })
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = '2022.02'
+    const apiCheck = new ApiCheck('test-check', {
+      name: 'Test Check',
+      request,
+    })
+    const payload = apiCheck.synthesize()
+    expect(payload.runtimeId).toBeUndefined()
+    delete Session.defaultRuntimeId
+  })
+
+  it('should synthesize runtime if specified', () => {
+    Session.project = new Project('project-id', {
+      name: 'Test Project',
+      repoUrl: 'https://github.com/checkly/checkly-cli',
+    })
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = '2022.02'
+    const apiCheck = new ApiCheck('test-check', {
+      name: 'Test Check',
+      runtimeId: '2022.02',
+      request,
+    })
+    const payload = apiCheck.synthesize()
+    expect(payload.runtimeId).toEqual('2022.02')
+    delete Session.defaultRuntimeId
+  })
+
   it('should apply default check settings', () => {
     Session.project = new Project('project-id', {
       name: 'Test Project',
diff --git a/packages/cli/src/constructs/__tests__/browser-check.spec.ts b/packages/cli/src/constructs/__tests__/browser-check.spec.ts
index dc782333..05017ff8 100644
--- a/packages/cli/src/constructs/__tests__/browser-check.spec.ts
+++ b/packages/cli/src/constructs/__tests__/browser-check.spec.ts
@@ -31,6 +31,84 @@ describe('BrowserCheck', () => {
     })
   })
 
+  it('should fail to bundle if runtime is not specified and default runtime is not set', () => {
+    const getFilePath = (filename: string) => path.join(__dirname, 'fixtures', 'api-check', filename)
+    const bundle = () => {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      const _bundle = BrowserCheck.bundle(getFilePath('entrypoint.js'), undefined)
+    }
+
+    Session.basePath = __dirname
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = undefined
+    expect(bundle).toThrowError('runtime is not set')
+    delete Session.basePath
+    delete Session.defaultRuntimeId
+  })
+
+  it('should successfully bundle if runtime is not specified but default runtime is set', () => {
+    const getFilePath = (filename: string) => path.join(__dirname, 'fixtures', 'api-check', filename)
+    const bundle = () => {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      const _bundle = BrowserCheck.bundle(getFilePath('entrypoint.js'), undefined)
+    }
+
+    Session.basePath = __dirname
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = '2022.10'
+    expect(bundle).not.toThrowError('is not supported')
+    delete Session.basePath
+    delete Session.defaultRuntimeId
+  })
+
+  it('should fail to bundle if runtime is not supported even if default runtime is set', () => {
+    const getFilePath = (filename: string) => path.join(__dirname, 'fixtures', 'api-check', filename)
+    const bundle = () => {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      const _bundle = BrowserCheck.bundle(getFilePath('entrypoint.js'), '9999.99')
+    }
+
+    Session.basePath = __dirname
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = '2022.02'
+    expect(bundle).toThrowError('9999.99 is not supported')
+    delete Session.basePath
+    delete Session.defaultRuntimeId
+  })
+
+  it('should not synthesize runtime if not specified even if default runtime is set', () => {
+    Session.project = new Project('project-id', {
+      name: 'Test Project',
+      repoUrl: 'https://github.com/checkly/checkly-cli',
+    })
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = '2022.02'
+    const browserCheck = new BrowserCheck('test-check', {
+      name: 'Test Check',
+      code: { content: 'console.log("test check")' },
+    })
+    const payload = browserCheck.synthesize()
+    expect(payload.runtimeId).toBeUndefined()
+    delete Session.defaultRuntimeId
+  })
+
+  it('should synthesize runtime if specified', () => {
+    Session.project = new Project('project-id', {
+      name: 'Test Project',
+      repoUrl: 'https://github.com/checkly/checkly-cli',
+    })
+    Session.availableRuntimes = runtimes
+    Session.defaultRuntimeId = '2022.02'
+    const browserCheck = new BrowserCheck('test-check', {
+      name: 'Test Check',
+      runtimeId: '2022.02',
+      code: { content: 'console.log("test check")' },
+    })
+    const payload = browserCheck.synthesize()
+    expect(payload.runtimeId).toEqual('2022.02')
+    delete Session.defaultRuntimeId
+  })
+
   it('should apply default check settings', () => {
     Session.project = new Project('project-id', {
       name: 'Test Project',
diff --git a/packages/cli/src/constructs/__tests__/multi-step-check.spec.ts b/packages/cli/src/constructs/__tests__/multi-step-check.spec.ts
index e24513d9..2087d0c0 100644
--- a/packages/cli/src/constructs/__tests__/multi-step-check.spec.ts
+++ b/packages/cli/src/constructs/__tests__/multi-step-check.spec.ts
@@ -19,6 +19,7 @@ describe('MultistepCheck', () => {
     })
     expect(check.synthesize()).toMatchObject({ checkType: 'MULTI_STEP' })
   })
+
   it('should throw if runtime does not support multi step check type', () => {
     Session.project = new Project('project-id', {
       name: 'Test Project',
@@ -33,7 +34,75 @@ describe('MultistepCheck', () => {
     }
     expect(() => new MultiStepCheck('main-check', {
       name: 'Main Check',
+      runtimeId: '2023.09',
       code: { content: '' },
     })).toThrowError('This runtime does not support multi step checks.')
   })
+
+  it('should throw if runtime is not set and default runtime does not support multi step check type', () => {
+    Session.project = new Project('project-id', {
+      name: 'Test Project',
+      repoUrl: 'https://github.com/checkly/checkly-cli',
+    })
+    Session.availableRuntimes = {
+      ...runtimesWithMultiStepSupport,
+      9999.99: {
+        ...runtimesWithMultiStepSupport['2023.09'],
+        multiStepSupport: false,
+      },
+    }
+    Session.defaultRuntimeId = '9999.99'
+    expect(() => new MultiStepCheck('main-check', {
+      name: 'Main Check',
+      code: { content: '' },
+    })).toThrowError('This runtime does not support multi step checks.')
+    delete Session.defaultRuntimeId
+  })
+
+  it('should succeed if runtime is not set but default runtime supports multi step check type', () => {
+    Session.project = new Project('project-id', {
+      name: 'Test Project',
+      repoUrl: 'https://github.com/checkly/checkly-cli',
+    })
+    Session.availableRuntimes = runtimesWithMultiStepSupport
+    Session.defaultRuntimeId = '2023.09'
+    expect(() => new MultiStepCheck('main-check', {
+      name: 'Main Check',
+      code: { content: '' },
+    })).not.toThrowError()
+    delete Session.defaultRuntimeId
+  })
+
+  it('should not synthesize runtime if not specified even if default runtime is set', () => {
+    Session.project = new Project('project-id', {
+      name: 'Test Project',
+      repoUrl: 'https://github.com/checkly/checkly-cli',
+    })
+    Session.availableRuntimes = runtimesWithMultiStepSupport
+    Session.defaultRuntimeId = '2023.09'
+    const multiCheck = new MultiStepCheck('main-check', {
+      name: 'Main Check',
+      code: { content: '' },
+    })
+    const payload = multiCheck.synthesize()
+    expect(payload.runtimeId).toBeUndefined()
+    delete Session.defaultRuntimeId
+  })
+
+  it('should synthesize runtime if specified', () => {
+    Session.project = new Project('project-id', {
+      name: 'Test Project',
+      repoUrl: 'https://github.com/checkly/checkly-cli',
+    })
+    Session.availableRuntimes = runtimesWithMultiStepSupport
+    Session.defaultRuntimeId = '2023.09'
+    const multiCheck = new MultiStepCheck('main-check', {
+      name: 'Main Check',
+      runtimeId: '2023.09',
+      code: { content: '' },
+    })
+    const payload = multiCheck.synthesize()
+    expect(payload.runtimeId).toEqual('2023.09')
+    delete Session.defaultRuntimeId
+  })
 })
diff --git a/packages/cli/src/constructs/api-check.ts b/packages/cli/src/constructs/api-check.ts
index 07eeeab7..5f3a7224 100644
--- a/packages/cli/src/constructs/api-check.ts
+++ b/packages/cli/src/constructs/api-check.ts
@@ -295,7 +295,7 @@ export class ApiCheck extends Check {
 
     if (props.setupScript) {
       if ('entrypoint' in props.setupScript) {
-        const { script, scriptPath, dependencies } = ApiCheck.bundle(props.setupScript.entrypoint, this.runtimeId!)
+        const { script, scriptPath, dependencies } = ApiCheck.bundle(props.setupScript.entrypoint, this.runtimeId)
         this.localSetupScript = script
         this.setupScriptPath = scriptPath
         this.setupScriptDependencies = dependencies
@@ -314,7 +314,7 @@ export class ApiCheck extends Check {
 
     if (props.tearDownScript) {
       if ('entrypoint' in props.tearDownScript) {
-        const { script, scriptPath, dependencies } = ApiCheck.bundle(props.tearDownScript.entrypoint, this.runtimeId!)
+        const { script, scriptPath, dependencies } = ApiCheck.bundle(props.tearDownScript.entrypoint, this.runtimeId)
         this.localTearDownScript = script
         this.tearDownScriptPath = scriptPath
         this.tearDownScriptDependencies = dependencies
@@ -337,7 +337,7 @@ export class ApiCheck extends Check {
     this.addPrivateLocationCheckAssignments()
   }
 
-  static bundle (entrypoint: string, runtimeId: string) {
+  static bundle (entrypoint: string, runtimeId?: string) {
     let absoluteEntrypoint = null
     if (path.isAbsolute(entrypoint)) {
       absoluteEntrypoint = entrypoint
@@ -348,7 +348,7 @@ export class ApiCheck extends Check {
       absoluteEntrypoint = path.join(path.dirname(Session.checkFileAbsolutePath), entrypoint)
     }
 
-    const runtime = Session.availableRuntimes[runtimeId]
+    const runtime = Session.getRuntime(runtimeId)
     if (!runtime) {
       throw new Error(`${runtimeId} is not supported`)
     }
diff --git a/packages/cli/src/constructs/browser-check.ts b/packages/cli/src/constructs/browser-check.ts
index fe13f7e1..ce139d16 100644
--- a/packages/cli/src/constructs/browser-check.ts
+++ b/packages/cli/src/constructs/browser-check.ts
@@ -79,8 +79,7 @@ export class BrowserCheck extends Check {
         }
         absoluteEntrypoint = path.join(path.dirname(Session.checkFileAbsolutePath), entrypoint)
       }
-      // runtimeId will always be set by check or browser check defaults so it is safe to use ! operator
-      const bundle = BrowserCheck.bundle(absoluteEntrypoint, this.runtimeId!)
+      const bundle = BrowserCheck.bundle(absoluteEntrypoint, this.runtimeId)
       if (!bundle.script) {
         throw new Error(`Browser check "${logicalId}" is not allowed to be empty`)
       }
@@ -115,8 +114,8 @@ export class BrowserCheck extends Check {
     }
   }
 
-  static bundle (entry: string, runtimeId: string) {
-    const runtime = Session.availableRuntimes[runtimeId]
+  static bundle (entry: string, runtimeId?: string) {
+    const runtime = Session.getRuntime(runtimeId)
     if (!runtime) {
       throw new Error(`${runtimeId} is not supported`)
     }
diff --git a/packages/cli/src/constructs/multi-step-check.ts b/packages/cli/src/constructs/multi-step-check.ts
index 89abc267..8e1500e9 100644
--- a/packages/cli/src/constructs/multi-step-check.ts
+++ b/packages/cli/src/constructs/multi-step-check.ts
@@ -47,7 +47,7 @@ export class MultiStepCheck extends Check {
 
     this.playwrightConfig = props.playwrightConfig
 
-    if (!Session.availableRuntimes[this.runtimeId!]?.multiStepSupport) {
+    if (!Session.getRuntime(this.runtimeId)?.multiStepSupport) {
       throw new Error('This runtime does not support multi step checks.')
     }
     if ('content' in props.code) {
@@ -65,7 +65,7 @@ export class MultiStepCheck extends Check {
         absoluteEntrypoint = path.join(path.dirname(Session.checkFileAbsolutePath), entrypoint)
       }
       // runtimeId will always be set by check or multi-step check defaults so it is safe to use ! operator
-      const bundle = MultiStepCheck.bundle(absoluteEntrypoint, this.runtimeId!)
+      const bundle = MultiStepCheck.bundle(absoluteEntrypoint, this.runtimeId)
       if (!bundle.script) {
         throw new Error(`Multi-Step check "${logicalId}" is not allowed to be empty`)
       }
@@ -99,8 +99,8 @@ export class MultiStepCheck extends Check {
     }
   }
 
-  static bundle (entry: string, runtimeId: string) {
-    const runtime = Session.availableRuntimes[runtimeId]
+  static bundle (entry: string, runtimeId?: string) {
+    const runtime = Session.getRuntime(runtimeId)
     if (!runtime) {
       throw new Error(`${runtimeId} is not supported`)
     }
diff --git a/packages/cli/src/constructs/project.ts b/packages/cli/src/constructs/project.ts
index 8d9d798a..169c96b1 100644
--- a/packages/cli/src/constructs/project.ts
+++ b/packages/cli/src/constructs/project.ts
@@ -142,6 +142,7 @@ export class Session {
   static checkFilePath?: string
   static checkFileAbsolutePath?: string
   static availableRuntimes: Record<string, Runtime>
+  static defaultRuntimeId?: string
   static verifyRuntimeDependencies = true
   static loadingChecklyConfigFile: boolean
   static checklyConfigFileConstructs?: Construct[]
@@ -153,7 +154,7 @@ export class Session {
     } else if (Session.loadingChecklyConfigFile && construct.allowInChecklyConfig()) {
       Session.checklyConfigFileConstructs!.push(construct)
     } else {
-      throw new Error('Internal Error: Session is not properly configured for using a construct. Please contact Checkly support on support@checklyhq.com')
+      throw new Error('Internal Error: Session is not properly configured for using a construct. Please contact Checkly support at support@checklyhq.com.')
     }
   }
 
@@ -182,4 +183,12 @@ export class Session {
     }
     return Session.privateLocations
   }
+
+  static getRuntime (runtimeId?: string): Runtime | undefined {
+    const effectiveRuntimeId = runtimeId ?? Session.defaultRuntimeId
+    if (effectiveRuntimeId === undefined) {
+      throw new Error('Internal Error: Account default runtime is not set. Please contact Checkly support at support@checklyhq.com.')
+    }
+    return Session.availableRuntimes[effectiveRuntimeId]
+  }
 }
diff --git a/packages/cli/src/rest/accounts.ts b/packages/cli/src/rest/accounts.ts
index 2a23b722..c7fdeb63 100644
--- a/packages/cli/src/rest/accounts.ts
+++ b/packages/cli/src/rest/accounts.ts
@@ -3,6 +3,7 @@ import type { AxiosInstance } from 'axios'
 export interface Account {
   id: string
   name: string
+  runtimeId: string
 }
 
 class Accounts {
diff --git a/packages/cli/src/services/__tests__/project-parser.spec.ts b/packages/cli/src/services/__tests__/project-parser.spec.ts
index e057c77c..4cf828b9 100644
--- a/packages/cli/src/services/__tests__/project-parser.spec.ts
+++ b/packages/cli/src/services/__tests__/project-parser.spec.ts
@@ -33,6 +33,7 @@ describe('parseProject()', () => {
       projectName: 'project name',
       repoUrl: 'https://github.com/checkly/checkly-cli',
       availableRuntimes: runtimes,
+      defaultRuntimeId: '2024.02',
     })
     const synthesizedProject = project.synthesize()
     expect(synthesizedProject).toMatchObject({
@@ -67,6 +68,7 @@ describe('parseProject()', () => {
       projectName: 'project name',
       repoUrl: 'https://github.com/checkly/checkly-cli',
       availableRuntimes: runtimes,
+      defaultRuntimeId: '2024.02',
     })
     const synthesizedProject = project.synthesize()
     expect(synthesizedProject).toMatchObject({
@@ -123,6 +125,7 @@ describe('parseProject()', () => {
       projectName: 'ts project',
       repoUrl: 'https://github.com/checkly/checkly-cli',
       availableRuntimes: runtimes,
+      defaultRuntimeId: '2024.02',
     })
     expect(project.synthesize()).toMatchObject({
       project: {
@@ -143,6 +146,7 @@ describe('parseProject()', () => {
       availableRuntimes: runtimes,
       checkMatch: ['**/__checks1__/*.check.js', '**/__checks2__/*.check.js', '**/__nested-checks__/*.check.js'],
       browserCheckMatch: ['**/__checks1__/*.spec.js', '**/__checks2__/*.spec.js', '**/__nested-checks__/*.spec.js'],
+      defaultRuntimeId: '2024.02',
     })
     expect(project.synthesize()).toMatchObject({
       project: {
@@ -170,6 +174,7 @@ describe('parseProject()', () => {
         availableRuntimes: runtimes,
         checkMatch: '**/*.foobar.js', // don't match .check.js files used for a different test
         browserCheckMatch: '**/*.spec.js',
+        defaultRuntimeId: '2024.02',
       })
       // shouldn't reach this point
       expect(true).toBe(false)
@@ -187,6 +192,7 @@ describe('parseProject()', () => {
         projectName: 'empty script project',
         repoUrl: 'https://github.com/checkly/checkly-cli',
         availableRuntimes: runtimes,
+        defaultRuntimeId: '2024.02',
         browserCheckMatch: '**/*.foobar.js', // don't match .spec.js files used for a different test
       })
       // shouldn't reach this point
@@ -203,6 +209,7 @@ describe('parseProject()', () => {
       projectLogicalId: 'glob-project-id',
       projectName: 'glob project',
       availableRuntimes: runtimes,
+      defaultRuntimeId: '2024.02',
       checkMatch: [],
       browserCheckMatch: ['**/__checks__/browser/*.spec.js'],
       multiStepCheckMatch: ['**/__checks__/multistep/*.spec.js'],
diff --git a/packages/cli/src/services/project-parser.ts b/packages/cli/src/services/project-parser.ts
index 1be67ee2..98845ba8 100644
--- a/packages/cli/src/services/project-parser.ts
+++ b/packages/cli/src/services/project-parser.ts
@@ -23,12 +23,12 @@ type ProjectParseOpts = {
   checkDefaults?: CheckConfigDefaults,
   browserCheckDefaults?: CheckConfigDefaults,
   availableRuntimes: Record<string, Runtime>,
+  defaultRuntimeId: string,
   verifyRuntimeDependencies?: boolean,
   checklyConfigConstructs?: Construct[],
 }
 
 const BASE_CHECK_DEFAULTS = {
-  runtimeId: '2024.02',
 }
 
 export async function parseProject (opts: ProjectParseOpts): Promise<Project> {
@@ -44,6 +44,7 @@ export async function parseProject (opts: ProjectParseOpts): Promise<Project> {
     checkDefaults = {},
     browserCheckDefaults = {},
     availableRuntimes,
+    defaultRuntimeId,
     verifyRuntimeDependencies,
     checklyConfigConstructs,
   } = opts
@@ -59,6 +60,7 @@ export async function parseProject (opts: ProjectParseOpts): Promise<Project> {
   Session.checkDefaults = Object.assign({}, BASE_CHECK_DEFAULTS, checkDefaults)
   Session.browserCheckDefaults = browserCheckDefaults
   Session.availableRuntimes = availableRuntimes
+  Session.defaultRuntimeId = defaultRuntimeId
   Session.verifyRuntimeDependencies = verifyRuntimeDependencies ?? true
 
   // TODO: Do we really need all of the ** globs, or could we just put node_modules?