diff --git a/crates/assistant/src/streaming_diff.rs b/crates/assistant/src/streaming_diff.rs
index 8383e081d53d427b562ad788c7670e52f15a7ef5..5c20dccadb95a5a5667d57161216ad896dfdef69 100644
--- a/crates/assistant/src/streaming_diff.rs
+++ b/crates/assistant/src/streaming_diff.rs
@@ -28,13 +28,36 @@ impl Matrix {
         self.cols = cols;
     }
 
+    fn swap_columns(&mut self, col1: usize, col2: usize) {
+        if col1 == col2 {
+            return;
+        }
+
+        if col1 >= self.cols {
+            panic!("column out of bounds");
+        }
+
+        if col2 >= self.cols {
+            panic!("column out of bounds");
+        }
+
+        unsafe {
+            let ptr = self.cells.as_mut_ptr();
+            std::ptr::swap_nonoverlapping(
+                ptr.add(col1 * self.rows),
+                ptr.add(col2 * self.rows),
+                self.rows,
+            );
+        }
+    }
+
     fn get(&self, row: usize, col: usize) -> f64 {
         if row >= self.rows {
             panic!("row out of bounds")
         }
 
         if col >= self.cols {
-            panic!("col out of bounds")
+            panic!("column out of bounds")
         }
         self.cells[col * self.rows + row]
     }
@@ -45,7 +68,7 @@ impl Matrix {
         }
 
         if col >= self.cols {
-            panic!("col out of bounds")
+            panic!("column out of bounds")
         }
 
         self.cells[col * self.rows + row] = value;
@@ -106,26 +129,32 @@ impl StreamingDiff {
 
     pub fn push_new(&mut self, text: &str) -> Vec<CharOperation> {
         self.new.extend(text.chars());
-        self.scores.resize(self.old.len() + 1, self.new.len() + 1);
+        self.scores.swap_columns(0, self.scores.cols - 1);
+        self.scores
+            .resize(self.old.len() + 1, self.new.len() - self.new_text_ix + 1);
+        self.equal_runs.retain(|(_i, j), _| *j == self.new_text_ix);
 
         for j in self.new_text_ix + 1..=self.new.len() {
-            self.scores.set(0, j, j as f64 * Self::INSERTION_SCORE);
+            let relative_j = j - self.new_text_ix;
+
+            self.scores
+                .set(0, relative_j, j as f64 * Self::INSERTION_SCORE);
             for i in 1..=self.old.len() {
-                let insertion_score = self.scores.get(i, j - 1) + Self::INSERTION_SCORE;
-                let deletion_score = self.scores.get(i - 1, j) + Self::DELETION_SCORE;
+                let insertion_score = self.scores.get(i, relative_j - 1) + Self::INSERTION_SCORE;
+                let deletion_score = self.scores.get(i - 1, relative_j) + Self::DELETION_SCORE;
                 let equality_score = if self.old[i - 1] == self.new[j - 1] {
                     let mut equal_run = self.equal_runs.get(&(i - 1, j - 1)).copied().unwrap_or(0);
                     equal_run += 1;
                     self.equal_runs.insert((i, j), equal_run);
 
                     let exponent = cmp::min(equal_run as i32 / 4, Self::MAX_EQUALITY_EXPONENT);
-                    self.scores.get(i - 1, j - 1) + Self::EQUALITY_BASE.powi(exponent)
+                    self.scores.get(i - 1, relative_j - 1) + Self::EQUALITY_BASE.powi(exponent)
                 } else {
                     f64::NEG_INFINITY
                 };
 
                 let score = insertion_score.max(deletion_score).max(equality_score);
-                self.scores.set(i, j, score);
+                self.scores.set(i, relative_j, score);
             }
         }
 
@@ -133,7 +162,7 @@ impl StreamingDiff {
         let mut next_old_text_ix = self.old_text_ix;
         let next_new_text_ix = self.new.len();
         for i in self.old_text_ix..=self.old.len() {
-            let score = self.scores.get(i, next_new_text_ix);
+            let score = self.scores.get(i, next_new_text_ix - self.new_text_ix);
             if score > max_score {
                 max_score = score;
                 next_old_text_ix = i;
@@ -174,7 +203,9 @@ impl StreamingDiff {
 
             let (prev_i, prev_j) = [insertion_score, deletion_score, equality_score]
                 .iter()
-                .max_by_key(|cell| cell.map(|(i, j)| OrderedFloat(self.scores.get(i, j))))
+                .max_by_key(|cell| {
+                    cell.map(|(i, j)| OrderedFloat(self.scores.get(i, j - self.new_text_ix)))
+                })
                 .unwrap()
                 .unwrap();