diff --git a/crates/ruff_python_formatter/src/comments/placement.rs b/crates/ruff_python_formatter/src/comments/placement.rs
index a730b52bbc..9af7b31bcf 100644
--- a/crates/ruff_python_formatter/src/comments/placement.rs
+++ b/crates/ruff_python_formatter/src/comments/placement.rs
@@ -1,7 +1,8 @@
 use ast::helpers::comment_indentation_after;
 use ruff_python_ast::whitespace::indentation;
 use ruff_python_ast::{
-    self as ast, AnyNodeRef, Comprehension, Expr, ModModule, Parameter, Parameters, StringLike,
+    self as ast, AnyNodeRef, Comprehension, Expr, ModModule, Parameter, ParameterWithDefault,
+    Parameters, StringLike,
 };
 use ruff_python_trivia::{
     BackwardsTokenizer, CommentRanges, SimpleToken, SimpleTokenKind, SimpleTokenizer,
@@ -205,6 +206,9 @@ fn handle_enclosed_comment<'a>(
             })
         }
         AnyNodeRef::Parameter(parameter) => handle_parameter_comment(comment, parameter, source),
+        AnyNodeRef::ParameterWithDefault(parameter) => {
+            handle_parameter_with_default_comment(comment, parameter, source)
+        }
         AnyNodeRef::Arguments(_) | AnyNodeRef::TypeParams(_) | AnyNodeRef::PatternArguments(_) => {
             handle_bracketed_end_of_line_comment(comment, source)
         }
@@ -864,43 +868,63 @@ fn handle_parameter_comment<'a>(
 
         assert_eq!(colon.kind(), SimpleTokenKind::Colon);
 
-        if comment.start() < colon.start() {
+        return if comment.start() < colon.start() {
             // The comment is before the colon, pull it out and make it a leading comment of the parameter.
             CommentPlacement::leading(parameter, comment)
         } else {
             CommentPlacement::Default(comment)
+        };
+    }
+
+    // If the comment falls before the parameter, and the grandparent node is a lambda (the
+    // parent node is always `Parameters`), make the comment a dangling lambda parameter, so
+    // that it can be formatted with the other dangling lambda comments in the lambda header.
+    //
+    // This is especially important for niche cases like:
+    //
+    // ```py
+    // (
+    //     lambda # comment 1
+    //     * # comment 2
+    //     x: # comment 3
+    //     x
+    // )
+    // ```
+    //
+    // where `# comment 2` otherwise becomes a leading comment on `*x` in the first format and a
+    // dangling comment on the lambda in the second. Instead, make it a dangling comment on the
+    // enclosing lambda from the start.
+    match comment.enclosing_grandparent() {
+        Some(AnyNodeRef::ExprLambda(lambda)) => return CommentPlacement::dangling(lambda, comment),
+        Some(AnyNodeRef::StmtExpr(ast::StmtExpr { value, .. })) if value.is_lambda_expr() => {
+            return CommentPlacement::dangling(&**value, comment);
         }
-    } else if comment.start() < parameter.name.start() {
-        // If the comment falls before the parameter, and the grandparent node is a lambda (the
-        // parent node is always `Parameters`), make the comment a dangling lambda parameter, so
-        // that it can be formatted with the other dangling lambda comments in the lambda header.
-        //
-        // This is especially important for niche cases like:
-        //
-        // ```py
-        // (
-        //     lambda # comment 1
-        //     * # comment 2
-        //     x: # comment 3
-        //     x
-        // )
-        // ```
-        //
-        // where `# comment 2` otherwise becomes a leading comment on `*x` in the first format and a
-        // dangling comment on the lambda in the second. Instead, make it a dangling comment on the
-        // enclosing lambda from the start.
-        match comment.enclosing_grandparent() {
-            Some(AnyNodeRef::ExprLambda(lambda)) => CommentPlacement::dangling(lambda, comment),
-            Some(AnyNodeRef::StmtExpr(ast::StmtExpr { value, .. })) if value.is_lambda_expr() => {
-                CommentPlacement::dangling(&**value, comment)
-            }
-            _ => CommentPlacement::leading(parameter, comment),
-        }
+        _ => {}
+    }
+
+    if comment.start() < parameter.name.start() {
+        CommentPlacement::leading(parameter, comment)
     } else {
         CommentPlacement::Default(comment)
     }
 }
 
+/// Handles parameters with defaults inside of lambda expressions by making them dangling comments
+/// on the lambda itself.
+fn handle_parameter_with_default_comment<'a>(
+    comment: DecoratedComment<'a>,
+    _parameter: &'a ParameterWithDefault,
+    _source: &str,
+) -> CommentPlacement<'a> {
+    match comment.enclosing_grandparent() {
+        Some(AnyNodeRef::ExprLambda(lambda)) => CommentPlacement::dangling(lambda, comment),
+        Some(AnyNodeRef::StmtExpr(ast::StmtExpr { value, .. })) if value.is_lambda_expr() => {
+            CommentPlacement::dangling(&**value, comment)
+        }
+        _ => CommentPlacement::Default(comment),
+    }
+}
+
 /// Handles comments between the left side and the operator of a binary expression (trailing comments of the left),
 /// and trailing end-of-line comments that are on the same line as the operator.
 ///
diff --git a/crates/ruff_python_formatter/src/expression/expr_lambda.rs b/crates/ruff_python_formatter/src/expression/expr_lambda.rs
index de363516b6..18ab36997b 100644
--- a/crates/ruff_python_formatter/src/expression/expr_lambda.rs
+++ b/crates/ruff_python_formatter/src/expression/expr_lambda.rs
@@ -35,8 +35,49 @@ impl FormatNodeRule<ExprLambda> for FormatExprLambda {
 
             // In this context, a dangling comment can either be a comment between the `lambda` and the
             // parameters, or a comment between the parameters and the body.
-            let (dangling_before_parameters, dangling_after_parameters) = dangling
-                .split_at(dangling.partition_point(|comment| comment.end() < parameters.start()));
+            let (dangling_before_parameters, dangling_after_parameters) =
+                // To prevent an instability in cases like:
+                //
+                // ```py
+                // (
+                //     lambda # comment 1
+                //     * # comment 2
+                //     x: # comment 3
+                //     x
+                // )
+                // ```
+                //
+                // `# comment 1` and `# comment 2` also become dangling comments on the lambda, so
+                // in preview, we include these in `dangling_after_parameters`, as long as the
+                // parameter list doesn't include any additional comments.
+                //
+                // This ends up formatted as:
+                //
+                // ```py
+                // (
+                //     lambda *x: (  # comment 1  # comment 2  # comment 3
+                //         x
+                //     )
+                // )
+                // ```
+                //
+                // instead of the stable formatting:
+                //
+                // ```py
+                // (
+                //     lambda  # comment 1
+                //     *x:  # comment 2
+                //     # comment 3
+                //     x
+                // )
+                // ```
+                if preview && !parameters_have_comments {
+                    ([].as_slice(), dangling)
+                } else {
+                    dangling.split_at(
+                        dangling.partition_point(|comment| comment.end() < parameters.start()),
+                    )
+                };
 
             if dangling_before_parameters.is_empty() {
                 write!(f, [space()])?;
diff --git a/crates/ruff_python_formatter/tests/snapshots/format@expression__lambda.py.snap b/crates/ruff_python_formatter/tests/snapshots/format@expression__lambda.py.snap
index 90aa73cc51..2aee975e1c 100644
--- a/crates/ruff_python_formatter/tests/snapshots/format@expression__lambda.py.snap
+++ b/crates/ruff_python_formatter/tests/snapshots/format@expression__lambda.py.snap
@@ -1513,7 +1513,7 @@ transform = (
  ):
      pass
  
-@@ -102,22 +83,25 @@
+@@ -102,58 +83,63 @@
  
  # Dangling comments without parameters.
  (
@@ -1549,15 +1549,34 @@ transform = (
  )
  
  (
-@@ -135,17 +119,18 @@
+-    lambda
+-    # comment
+-    *x: x
++    lambda *x: (
++        # comment
++        x
++    )
+ )
+ 
  (
-     lambda
-     # comment 1
+-    lambda
+-    # comment
+-    *x, **y: x
++    lambda *x, **y: (
++        # comment
++        x
++    )
+ )
+ 
+ (
+-    lambda
+-    # comment 1
 -    *x:
 -    # comment 2
 -    # comment 3
 -    x
-+    *x: (
++    lambda *x: (
++        # comment 1
 +        # comment 2
 +        # comment 3
 +        x
@@ -1565,17 +1584,29 @@ transform = (
  )
  
  (
-     lambda  # comment 1
+-    lambda  # comment 1
 -    *x:  # comment 2
 -    # comment 3
 -    x
-+    *x: (  # comment 2  # comment 3
++    lambda *x: (  # comment 1  # comment 2  # comment 3
 +        x
 +    )
  )
  
  lambda *x: x
-@@ -161,30 +146,34 @@
+ 
+ (
+-    lambda
+-    # comment
+-    *x: x
++    lambda *x: (
++        # comment
++        x
++    )
+ )
+ 
+ lambda: (  # comment
+@@ -161,42 +147,47 @@
  )
  
  (
@@ -1622,16 +1653,18 @@ transform = (
          x
      )
  )
-@@ -192,11 +181,12 @@
+ 
  (
-     lambda  # 1
-     # 2
+-    lambda  # 1
+-    # 2
 -    x:  # 3
 -    # 4
 -    # 5
 -    # 6
 -    x
-+    x: (  # 3
++    lambda x: (  # 1
++        # 2
++        # 3
 +        # 4
 +        # 5
 +        # 6
@@ -1640,7 +1673,7 @@ transform = (
  )
  
  (
-@@ -204,9 +194,10 @@
+@@ -204,9 +195,10 @@
      # 2
      x,  # 3
      # 4
@@ -1654,7 +1687,7 @@ transform = (
  )
  
  (
-@@ -218,71 +209,79 @@
+@@ -218,71 +210,79 @@
  
  # Leading
  lambda x: (
@@ -1793,7 +1826,7 @@ transform = (
  
  
  # Regression tests for https://github.com/astral-sh/ruff/issues/8179
-@@ -291,9 +290,9 @@
+@@ -291,9 +291,9 @@
          c,
          d,
          e,
@@ -1806,7 +1839,7 @@ transform = (
      )
  
  
-@@ -302,15 +301,9 @@
+@@ -302,15 +302,9 @@
          c,
          d,
          e,
@@ -1825,7 +1858,7 @@ transform = (
          g=10,
      )
  
-@@ -320,9 +313,9 @@
+@@ -320,9 +314,9 @@
          c,
          d,
          e,
@@ -1838,7 +1871,7 @@ transform = (
      )
  
  
-@@ -338,9 +331,9 @@
+@@ -338,9 +332,9 @@
  
  class C:
      function_dict: Dict[Text, Callable[[CRFToken], Any]] = {
@@ -1851,7 +1884,7 @@ transform = (
      }
  
  
-@@ -352,42 +345,40 @@
+@@ -352,42 +346,40 @@
  def foo():
      if True:
          if True:
@@ -1910,7 +1943,7 @@ transform = (
          CREATE TABLE {table} AS
          SELECT ROW_NUMBER() OVER () AS id, {var}
          FROM (
-@@ -402,18 +393,19 @@
+@@ -402,18 +394,19 @@
  long_assignment_target.with_attribute.and_a_slice[with_an_index] = (
      # 1
      # 2
@@ -1937,7 +1970,7 @@ transform = (
  )
  
  very_long_variable_name_x, very_long_variable_name_y = (
-@@ -421,8 +413,8 @@
+@@ -421,8 +414,8 @@
      lambda b: b * another_very_long_expression_here,
  )
  
@@ -1948,7 +1981,7 @@ transform = (
          x, more_args, additional_parameters
      )
  )
-@@ -458,12 +450,12 @@
+@@ -458,12 +451,12 @@
      [
          # Not fluent
          param(
@@ -1963,7 +1996,7 @@ transform = (
          ),
          param(
              lambda left, right: (
-@@ -472,9 +464,9 @@
+@@ -472,9 +465,9 @@
          ),
          param(lambda left, right: ibis.timestamp("2017-04-01").cast(dt.date)),
          param(
@@ -1976,7 +2009,7 @@ transform = (
          ),
          # This is too long on one line in the lambda body and gets wrapped
          # inside the body.
-@@ -508,16 +500,18 @@
+@@ -508,16 +501,18 @@
  ]
  
  # adds parentheses around the body
@@ -1998,7 +2031,7 @@ transform = (
  
  lambda x, y, z: (
      x + y + z
-@@ -528,7 +522,7 @@
+@@ -528,7 +523,7 @@
      x + y + z  # trailing eol body
  )
  
@@ -2007,7 +2040,7 @@ transform = (
  
  lambda x, y, z: (
      # leading body
-@@ -540,21 +534,23 @@
+@@ -540,21 +535,23 @@
  )
  
  (
@@ -2041,7 +2074,7 @@ transform = (
      # dangling header comment
      source_bucket
      if name == source_bucket_name
-@@ -562,8 +558,7 @@
+@@ -562,8 +559,7 @@
  )
  
  (
@@ -2051,7 +2084,7 @@ transform = (
          source_bucket
          if name == source_bucket_name
          else storage.Bucket(mock_service, destination_bucket_name)
-@@ -571,61 +566,70 @@
+@@ -571,61 +567,70 @@
  )
  
  (
@@ -2154,47 +2187,52 @@ transform = (
  )
  
  (
-@@ -638,27 +642,31 @@
+@@ -636,29 +641,30 @@
+ )
+ 
  (
-     lambda
-     # comment
+-    lambda
+-    # comment
 -    *args, **kwargs: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs)
 -    + 1
-+    *args, **kwargs: (
++    lambda *args, **kwargs: (
++        # comment
 +        aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs) + 1
 +    )
  )
  
  (
-     lambda  # comment
+-    lambda  # comment
 -    *args, **kwargs: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs)
 -    + 1
-+    *args, **kwargs: (
++    lambda *args, **kwargs: (  # comment
 +        aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs) + 1
 +    )
  )
  
  (
-     lambda  # comment 1
-     # comment 2
+-    lambda  # comment 1
+-    # comment 2
 -    *args, **kwargs:  # comment 3
 -    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs) + 1
-+    *args, **kwargs: (  # comment 3
++    lambda *args, **kwargs: (  # comment 1
++        # comment 2
++        # comment 3
 +        aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs) + 1
 +    )
  )
  
  (
-     lambda  # comment 1
+-    lambda  # comment 1
 -    *args, **kwargs:  # comment 3
 -    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs) + 1
-+    *args, **kwargs: (  # comment 3
++    lambda *args, **kwargs: (  # comment 1  # comment 3
 +        aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs) + 1
 +    )
  )
  
  (
-@@ -666,19 +674,20 @@
+@@ -666,19 +672,20 @@
      # 2
      left,  # 3
      # 4
@@ -2225,7 +2263,7 @@ transform = (
          )
      )
  )
-@@ -696,46 +705,50 @@
+@@ -696,46 +703,50 @@
  foo(
      lambda from_ts,  # but still wrap the body if it gets too long
      to_ts,