diff --git a/claudetool/differential.go b/claudetool/differential.go
index 014fc13..710a09d 100644
--- a/claudetool/differential.go
+++ b/claudetool/differential.go
@@ -2,6 +2,7 @@
 
 import (
 	"bytes"
+	"cmp"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -12,8 +13,10 @@
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"slices"
 	"strings"
+	"sync"
 	"time"
 
 	"golang.org/x/tools/go/packages"
@@ -78,7 +81,20 @@
 	}
 	allPkgList := slices.Collect(maps.Keys(allPkgs))
 
-	var msgs []string
+	var errorMessages []string // problems we want the model to address
+	var infoMessages []string  // info the model should consider
+
+	// Find potentially related files that should also be considered
+	// TODO: add some caching here, since this depends only on the initial commit and the changed files, not the details of the changes
+	relatedFiles, err := r.findRelatedFiles(ctx, changedFiles)
+	if err != nil {
+		slog.DebugContext(ctx, "CodeReviewer.Run: failed to find related files", "err", err)
+	} else {
+		relatedMsg := r.formatRelatedFiles(relatedFiles)
+		if relatedMsg != "" {
+			infoMessages = append(infoMessages, relatedMsg)
+		}
+	}
 
 	testMsg, err := r.checkTests(ctx, allPkgList)
 	if err != nil {
@@ -86,7 +102,7 @@
 		return "", err
 	}
 	if testMsg != "" {
-		msgs = append(msgs, testMsg)
+		errorMessages = append(errorMessages, testMsg)
 	}
 
 	goplsMsg, err := r.checkGopls(ctx, changedFiles) // includes vet checks
@@ -95,17 +111,24 @@
 		return "", err
 	}
 	if goplsMsg != "" {
-		msgs = append(msgs, goplsMsg)
+		errorMessages = append(errorMessages, goplsMsg)
 	}
 
-	if len(msgs) == 0 {
-		slog.DebugContext(ctx, "CodeReviewer.Run: no issues found")
-		return "OK", nil
+	buf := new(strings.Builder)
+	if len(infoMessages) > 0 {
+		buf.WriteString("# Info\n\n")
+		buf.WriteString(strings.Join(infoMessages, "\n\n"))
+		buf.WriteString("\n\n")
 	}
-
-	msgs = append(msgs, "Please fix before proceeding.")
-	slog.DebugContext(ctx, "CodeReviewer.Run: found issues", "issues", msgs)
-	return strings.Join(msgs, "\n\n"), nil
+	if len(errorMessages) > 0 {
+		buf.WriteString("# Errors\n\n")
+		buf.WriteString(strings.Join(errorMessages, "\n\n"))
+		buf.WriteString("\n\nPlease fix before proceeding.\n")
+	}
+	if buf.Len() == 0 {
+		buf.WriteString("OK")
+	}
+	return buf.String(), nil
 }
 
 func (r *CodeReviewer) initializeInitialCommitWorktree(ctx context.Context) error {
@@ -845,3 +868,161 @@
 
 	return buf.String()
 }
+
+// RelatedFile represents a file historically related to the changed files
+type RelatedFile struct {
+	Path        string  // Path to the file
+	Correlation float64 // Correlation score (0.0-1.0)
+}
+
+// findRelatedFiles identifies files that are historically related to the changed files
+// by analyzing git commit history for co-occurrences.
+func (r *CodeReviewer) findRelatedFiles(ctx context.Context, changedFiles []string) ([]RelatedFile, error) {
+	commits, err := r.getCommitsTouchingFiles(ctx, changedFiles)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get commits touching files: %w", err)
+	}
+	if len(commits) == 0 {
+		return nil, nil
+	}
+
+	relChanged := make(map[string]bool, len(changedFiles))
+	for _, file := range changedFiles {
+		rel, err := filepath.Rel(r.repoRoot, file)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get relative path for %s: %w", file, err)
+		}
+		relChanged[rel] = true
+	}
+
+	historyFiles := make(map[string]int)
+	var historyMu sync.Mutex
+
+	maxWorkers := runtime.GOMAXPROCS(0)
+	semaphore := make(chan bool, maxWorkers)
+	var wg sync.WaitGroup
+
+	for _, commit := range commits {
+		wg.Add(1)
+		semaphore <- true // acquire
+
+		go func(commit string) {
+			defer wg.Done()
+			defer func() { <-semaphore }() // release
+			commitFiles, err := r.getFilesInCommit(ctx, commit)
+			if err != nil {
+				slog.WarnContext(ctx, "Failed to get files in commit", "commit", commit, "err", err)
+				return
+			}
+			incr := 0
+			for _, file := range commitFiles {
+				if relChanged[file] {
+					incr++
+				}
+			}
+			if incr == 0 {
+				return
+			}
+			historyMu.Lock()
+			defer historyMu.Unlock()
+			for _, file := range commitFiles {
+				historyFiles[file] += incr
+			}
+		}(commit)
+	}
+	wg.Wait()
+
+	// normalize
+	maxCount := 0
+	for _, count := range historyFiles {
+		maxCount = max(maxCount, count)
+	}
+	if maxCount == 0 {
+		return nil, nil
+	}
+
+	var relatedFiles []RelatedFile
+	for file, count := range historyFiles {
+		if relChanged[file] {
+			// Don't include inputs in the output.
+			continue
+		}
+		correlation := float64(count) / float64(maxCount)
+		// Require min correlation to avoid noise
+		if correlation >= 0.1 {
+			relatedFiles = append(relatedFiles, RelatedFile{Path: file, Correlation: correlation})
+		}
+	}
+
+	// Highest correlation first
+	slices.SortFunc(relatedFiles, func(a, b RelatedFile) int {
+		return -1 * cmp.Compare(a.Correlation, b.Correlation)
+	})
+
+	// Limit to 1 correlated file per input file.
+	// (Arbitrary limit, to be adjusted.)
+	maxFiles := len(changedFiles)
+	if len(relatedFiles) > maxFiles {
+		relatedFiles = relatedFiles[:maxFiles]
+	}
+
+	// TODO: add an LLM in the mix here (like the keyword search tool) to do a filtering pass,
+	// and then increase the strength of the wording in the relatedFiles message.
+
+	return relatedFiles, nil
+}
+
+// getCommitsTouchingFiles returns all commits that touch any of the specified files
+func (r *CodeReviewer) getCommitsTouchingFiles(ctx context.Context, files []string) ([]string, error) {
+	if len(files) == 0 {
+		return nil, nil
+	}
+	fileArgs := append([]string{"rev-list", "--all", "--"}, files...)
+	cmd := exec.CommandContext(ctx, "git", fileArgs...)
+	cmd.Dir = r.repoRoot
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get commits: %w\n%s", err, out)
+	}
+	return nonEmptyTrimmedLines(out), nil
+}
+
+// getFilesInCommit returns all files changed in a specific commit
+func (r *CodeReviewer) getFilesInCommit(ctx context.Context, commit string) ([]string, error) {
+	cmd := exec.CommandContext(ctx, "git", "diff-tree", "--no-commit-id", "--name-only", "-r", commit)
+	cmd.Dir = r.repoRoot
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get files in commit: %w\n%s", err, out)
+	}
+	return nonEmptyTrimmedLines(out), nil
+}
+
+func nonEmptyTrimmedLines(b []byte) []string {
+	var lines []string
+	for line := range strings.Lines(string(b)) {
+		line = strings.TrimSpace(line)
+		if line != "" {
+			lines = append(lines, line)
+		}
+	}
+	return lines
+}
+
+// formatRelatedFiles formats the related files list into a human-readable message
+func (r *CodeReviewer) formatRelatedFiles(files []RelatedFile) string {
+	if len(files) == 0 {
+		return ""
+	}
+
+	buf := new(strings.Builder)
+
+	fmt.Fprintf(buf, "Potentially related files:\n\n")
+
+	for _, file := range files {
+		fmt.Fprintf(buf, "- %s (%0.0f%%)\n", file.Path, 100*file.Correlation)
+	}
+
+	fmt.Fprintf(buf, "\nThese files have historically changed with the files you have modified. Consider whether they require updates as well.\n")
+	return buf.String()
+}