option-1.patch

diff --git a/Grammar/Grammar b/Grammar/Grammar
index 94898d3..9c74096 100644
--- a/Grammar/Grammar
+++ b/Grammar/Grammar
@@ -21,8 +21,11 @@ eval_input: testlist NEWLINE* ENDMARKER
 
 decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE
 decorators: decorator+
-decorated: decorators (classdef | funcdef)
-funcdef: 'def' NAME parameters ['->' test] ':' suite
+decorated: decorators (classdef | funcdef | async_funcdef)
+
+async_funcdef: ASYNC funcdef
+funcdef: ('def' NAME parameters ['->' test] ':' suite)
+
 parameters: '(' [typedargslist] ')'
 typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])* [','
        ['*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef]]
@@ -37,18 +40,19 @@ stmt: simple_stmt | compound_stmt
 simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE
 small_stmt: (expr_stmt | del_stmt | pass_stmt | flow_stmt |
              import_stmt | global_stmt | nonlocal_stmt | assert_stmt)
-expr_stmt: testlist_star_expr (augassign (yield_expr|testlist) |
-                     ('=' (yield_expr|testlist_star_expr))*)
+expr_stmt: testlist_star_expr (augassign (yield_expr|await_expr|testlist) |
+                     ('=' (yield_expr|await_expr|testlist_star_expr))*)
 testlist_star_expr: (test|star_expr) (',' (test|star_expr))* [',']
 augassign: ('+=' | '-=' | '*=' | '@=' | '/=' | '%=' | '&=' | '|=' | '^=' |
             '<<=' | '>>=' | '**=' | '//=')
 # For normal assignments, additional restrictions enforced by the interpreter
 del_stmt: 'del' exprlist
 pass_stmt: 'pass'
-flow_stmt: break_stmt | continue_stmt | return_stmt | raise_stmt | yield_stmt
+flow_stmt: break_stmt | continue_stmt | return_stmt | raise_stmt | yield_stmt | await_stmt
 break_stmt: 'break'
 continue_stmt: 'continue'
 return_stmt: 'return' [testlist]
+await_stmt: await_expr
 yield_stmt: yield_expr
 raise_stmt: 'raise' [test ['from' test]]
 import_stmt: import_name | import_from
@@ -65,7 +69,9 @@ global_stmt: 'global' NAME (',' NAME)*
 nonlocal_stmt: 'nonlocal' NAME (',' NAME)*
 assert_stmt: 'assert' test [',' test]
 
-compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated
+compound_stmt: (if_stmt | while_stmt | for_stmt | try_stmt | with_stmt
+                | funcdef | classdef | decorated | async_stmt)
+async_stmt: ASYNC (funcdef | with_stmt | for_stmt)
 if_stmt: 'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite]
 while_stmt: 'while' test ':' suite ['else' ':' suite]
 for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
@@ -100,7 +106,7 @@ arith_expr: term (('+'|'-') term)*
 term: factor (('*'|'@'|'/'|'%'|'//') factor)*
 factor: ('+'|'-'|'~') factor | power
 power: atom trailer* ['**' factor]
-atom: ('(' [yield_expr|testlist_comp] ')' |
+atom: ('(' [yield_expr|await_expr|testlist_comp] ')' |
        '[' [testlist_comp] ']' |
        '{' [dictorsetmaker] '}' |
        NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False')
@@ -129,5 +135,7 @@ comp_if: 'if' test_nocond [comp_iter]
 # not used in grammar, but may appear in "node" passed from Parser to Compiler
 encoding_decl: NAME
 
+await_expr: AWAIT test
+
 yield_expr: 'yield' [yield_arg]
 yield_arg: 'from' test | testlist

option-2.patch

diff --git a/Grammar/Grammar b/Grammar/Grammar
index 94898d3..027aa61 100644
--- a/Grammar/Grammar
+++ b/Grammar/Grammar
@@ -21,8 +21,11 @@ eval_input: testlist NEWLINE* ENDMARKER
 
 decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE
 decorators: decorator+
-decorated: decorators (classdef | funcdef)
-funcdef: 'def' NAME parameters ['->' test] ':' suite
+decorated: decorators (classdef | funcdef | async_funcdef)
+
+async_funcdef: ASYNC funcdef
+funcdef: ('def' NAME parameters ['->' test] ':' suite)
+
 parameters: '(' [typedargslist] ')'
 typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])* [','
        ['*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef]]
@@ -65,7 +68,9 @@ global_stmt: 'global' NAME (',' NAME)*
 nonlocal_stmt: 'nonlocal' NAME (',' NAME)*
 assert_stmt: 'assert' test [',' test]
 
-compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated
+compound_stmt: (if_stmt | while_stmt | for_stmt | try_stmt | with_stmt
+                | funcdef | classdef | decorated | async_stmt)
+async_stmt: ASYNC (funcdef | with_stmt | for_stmt)
 if_stmt: 'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite]
 while_stmt: 'while' test ':' suite ['else' ':' suite]
 for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
@@ -103,7 +108,8 @@ power: atom trailer* ['**' factor]
 atom: ('(' [yield_expr|testlist_comp] ')' |
        '[' [testlist_comp] ']' |
        '{' [dictorsetmaker] '}' |
-       NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False')
+       NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False' |
+       await_expr)
 testlist_comp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
 trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']
@@ -129,5 +135,7 @@ comp_if: 'if' test_nocond [comp_iter]
 # not used in grammar, but may appear in "node" passed from Parser to Compiler
 encoding_decl: NAME
 
+await_expr: AWAIT test
+
 yield_expr: 'yield' [yield_arg]
 yield_arg: 'from' test | testlist

option-3.patch

diff --git a/Grammar/Grammar b/Grammar/Grammar
index 94898d3..9a880c6 100644
--- a/Grammar/Grammar
+++ b/Grammar/Grammar
@@ -21,8 +21,11 @@ eval_input: testlist NEWLINE* ENDMARKER
 
 decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE
 decorators: decorator+
-decorated: decorators (classdef | funcdef)
-funcdef: 'def' NAME parameters ['->' test] ':' suite
+decorated: decorators (classdef | funcdef | async_funcdef)
+
+async_funcdef: ASYNC funcdef
+funcdef: ('def' NAME parameters ['->' test] ':' suite)
+
 parameters: '(' [typedargslist] ')'
 typedargslist: (tfpdef ['=' test] (',' tfpdef ['=' test])* [','
        ['*' [tfpdef] (',' tfpdef ['=' test])* [',' '**' tfpdef] | '**' tfpdef]]
@@ -65,7 +68,9 @@ global_stmt: 'global' NAME (',' NAME)*
 nonlocal_stmt: 'nonlocal' NAME (',' NAME)*
 assert_stmt: 'assert' test [',' test]
 
-compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated
+compound_stmt: (if_stmt | while_stmt | for_stmt | try_stmt | with_stmt
+                | funcdef | classdef | decorated | async_stmt)
+async_stmt: ASYNC (funcdef | with_stmt | for_stmt)
 if_stmt: 'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite]
 while_stmt: 'while' test ':' suite ['else' ':' suite]
 for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
@@ -99,7 +104,8 @@ shift_expr: arith_expr (('<<'|'>>') arith_expr)*
 arith_expr: term (('+'|'-') term)*
 term: factor (('*'|'@'|'/'|'%'|'//') factor)*
 factor: ('+'|'-'|'~') factor | power
-power: atom trailer* ['**' factor]
+power: atom_expr ['**' factor]
+atom_expr: [AWAIT] atom trailer*
 atom: ('(' [yield_expr|testlist_comp] ')' |
        '[' [testlist_comp] ']' |
        '{' [dictorsetmaker] '}' |

Referenced from https://mail.python.org/pipermail/python-dev/2015-April/139541.html