diff --git a/packages/core/__tests__/lib.test.ts b/packages/core/__tests__/lib.test.ts
index dc34213f..9c9b4970 100644
--- a/packages/core/__tests__/lib.test.ts
+++ b/packages/core/__tests__/lib.test.ts
@@ -33,29 +33,29 @@ describe('@actions/core', () => {
 
   it('exportVariable produces the correct command and sets the env', () => {
     core.exportVariable('my var', 'var val')
-    assertWriteCalls([`##[set-env name=my var;]var val${os.EOL}`])
+    assertWriteCalls([`::set-env name=my var,::var val${os.EOL}`])
   })
 
   it('exportVariable escapes variable names', () => {
     core.exportVariable('special char var \r\n];', 'special val')
     expect(process.env['special char var \r\n];']).toBe('special val')
     assertWriteCalls([
-      `##[set-env name=special char var %0D%0A%5D%3B;]special val${os.EOL}`
+      `::set-env name=special char var %0D%0A%5D%3B,::special val${os.EOL}`
     ])
   })
 
   it('exportVariable escapes variable values', () => {
     core.exportVariable('my var2', 'var val\r\n')
     expect(process.env['my var2']).toBe('var val\r\n')
-    assertWriteCalls([`##[set-env name=my var2;]var val%0D%0A${os.EOL}`])
+    assertWriteCalls([`::set-env name=my var2,::var val%0D%0A${os.EOL}`])
   })
 
   // it('exportSecret produces the correct commands and sets the env', () => {
   //   core.exportSecret('my secret', 'secret val')
   //   expect(process.env['my secret']).toBe('secret val')
   //   assertWriteCalls([
-  //     `##[set-env name=my secret;]secret val${os.EOL}`,
-  //     `##[set-secret]secret val${os.EOL}`
+  //     `::set-env name=my secret,::secret val${os.EOL}`,
+  //     `::set-secret]secret val${os.EOL}`
   //   ])
   // })
 
@@ -63,10 +63,10 @@ describe('@actions/core', () => {
   //   core.exportSecret('special char secret \r\n];', 'special secret val')
   //   expect(process.env['special char secret \r\n];']).toBe('special secret val')
   //   assertWriteCalls([
-  //     `##[set-env name=special char secret %0D%0A%5D%3B;]special secret val${
+  //     `::set-env name=special char secret %0D%0A%5D%3B,::special secret val${
   //       os.EOL
   //     }`,
-  //     `##[set-secret]special secret val${os.EOL}`
+  //     `::set-secret]special secret val${os.EOL}`
   //   ])
   // })
 
@@ -74,8 +74,8 @@ describe('@actions/core', () => {
   //   core.exportSecret('my secret2', 'secret val\r\n')
   //   expect(process.env['my secret2']).toBe('secret val\r\n')
   //   assertWriteCalls([
-  //     `##[set-env name=my secret2;]secret val%0D%0A${os.EOL}`,
-  //     `##[set-secret]secret val%0D%0A${os.EOL}`
+  //     `::set-env name=my secret2,::secret val%0D%0A${os.EOL}`,
+  //     `::set-secret]secret val%0D%0A${os.EOL}`
   //   ])
   // })
 
@@ -84,7 +84,7 @@ describe('@actions/core', () => {
     expect(process.env['PATH']).toBe(
       `myPath${path.delimiter}path1${path.delimiter}path2`
     )
-    assertWriteCalls([`##[add-path]myPath${os.EOL}`])
+    assertWriteCalls([`::add-path::myPath${os.EOL}`])
   })
 
   it('getInput gets non-required input', () => {
@@ -115,7 +115,7 @@ describe('@actions/core', () => {
 
   it('setOutput produces the correct command', () => {
     core.setOutput('some output', 'some value')
-    assertWriteCalls([`##[set-output name=some output;]some value${os.EOL}`])
+    assertWriteCalls([`::set-output name=some output,::some value${os.EOL}`])
   })
 
   it('setNeutral sets the correct exit code', () => {
@@ -126,33 +126,33 @@ describe('@actions/core', () => {
   it('setFailure sets the correct exit code and failure message', () => {
     core.setFailed('Failure message')
     expect(process.exitCode).toBe(core.ExitCode.Failure)
-    assertWriteCalls([`##[error]Failure message${os.EOL}`])
+    assertWriteCalls([`::error::Failure message${os.EOL}`])
   })
 
   it('setFailure escapes the failure message', () => {
     core.setFailed('Failure \r\n\nmessage\r')
     expect(process.exitCode).toBe(core.ExitCode.Failure)
-    assertWriteCalls([`##[error]Failure %0D%0A%0Amessage%0D${os.EOL}`])
+    assertWriteCalls([`::error::Failure %0D%0A%0Amessage%0D${os.EOL}`])
   })
 
   it('error sets the correct error message', () => {
     core.error('Error message')
-    assertWriteCalls([`##[error]Error message${os.EOL}`])
+    assertWriteCalls([`::error::Error message${os.EOL}`])
   })
 
   it('error escapes the error message', () => {
     core.error('Error message\r\n\n')
-    assertWriteCalls([`##[error]Error message%0D%0A%0A${os.EOL}`])
+    assertWriteCalls([`::error::Error message%0D%0A%0A${os.EOL}`])
   })
 
   it('warning sets the correct message', () => {
     core.warning('Warning')
-    assertWriteCalls([`##[warning]Warning${os.EOL}`])
+    assertWriteCalls([`::warning::Warning${os.EOL}`])
   })
 
   it('warning escapes the message', () => {
     core.warning('\r\nwarning\n')
-    assertWriteCalls([`##[warning]%0D%0Awarning%0A${os.EOL}`])
+    assertWriteCalls([`::warning::%0D%0Awarning%0A${os.EOL}`])
   })
 
   it('startGroup starts a new group', () => {
@@ -180,12 +180,12 @@ describe('@actions/core', () => {
 
   it('debug sets the correct message', () => {
     core.debug('Debug')
-    assertWriteCalls([`##[debug]Debug${os.EOL}`])
+    assertWriteCalls([`::debug::Debug${os.EOL}`])
   })
 
   it('debug escapes the message', () => {
     core.debug('\r\ndebug\n')
-    assertWriteCalls([`##[debug]%0D%0Adebug%0A${os.EOL}`])
+    assertWriteCalls([`::debug::%0D%0Adebug%0A${os.EOL}`])
   })
 })
 
diff --git a/packages/core/package-lock.json b/packages/core/package-lock.json
index 6aee4fab..601a131a 100644
--- a/packages/core/package-lock.json
+++ b/packages/core/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "@actions/core",
-  "version": "1.0.0",
+  "version": "1.0.1",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/packages/core/src/command.ts b/packages/core/src/command.ts
index 4e6e9b41..0773a724 100644
--- a/packages/core/src/command.ts
+++ b/packages/core/src/command.ts
@@ -29,7 +29,7 @@ export function issue(name: string, message: string = ''): void {
   issueCommand(name, {}, message)
 }
 
-const CMD_PREFIX = '##['
+const CMD_STRING = '::'
 
 class Command {
   private readonly command: string
@@ -47,7 +47,7 @@ class Command {
   }
 
   toString(): string {
-    let cmdStr = CMD_PREFIX + this.command
+    let cmdStr = CMD_STRING + this.command
 
     if (this.properties && Object.keys(this.properties).length > 0) {
       cmdStr += ' '
@@ -57,13 +57,13 @@ class Command {
           if (val) {
             // safely append the val - avoid blowing up when attempting to
             // call .replace() if message is not a string for some reason
-            cmdStr += `${key}=${escape(`${val || ''}`)};`
+            cmdStr += `${key}=${escape(`${val || ''}`)},`
           }
         }
       }
     }
 
-    cmdStr += ']'
+    cmdStr += CMD_STRING
 
     // safely append the message - avoid blowing up when attempting to
     // call .replace() if message is not a string for some reason