diff --git a/llm/gem/gem_test.go b/llm/gem/gem_test.go
index 7518d49..002b4d1 100644
--- a/llm/gem/gem_test.go
+++ b/llm/gem/gem_test.go
@@ -1,7 +1,11 @@
 package gem
 
 import (
+	"bytes"
+	"context"
 	"encoding/json"
+	"io"
+	"net/http"
 	"testing"
 
 	"sketch.dev/llm"
@@ -216,3 +220,147 @@
 		t.Fatalf("Expected command 'cat README.md', got '%s'", cmd)
 	}
 }
+
+func TestGeminiHeaderCapture(t *testing.T) {
+	// Create a mock HTTP client that returns a response with headers
+	mockClient := &http.Client{
+		Transport: &mockRoundTripper{
+			response: &http.Response{
+				StatusCode: http.StatusOK,
+				Header: http.Header{
+					"Content-Type":            []string{"application/json"},
+					"Skaband-Cost-Microcents": []string{"123456"},
+				},
+				Body: io.NopCloser(bytes.NewBufferString(`{
+					"candidates": [{
+						"content": {
+							"parts": [{
+								"text": "Hello!"
+							}]
+						}
+					}]
+				}`)),
+			},
+		},
+	}
+
+	// Create a Gemini model with the mock client
+	model := gemini.Model{
+		Model:    "models/gemini-test",
+		APIKey:   "test-key",
+		HTTPC:    mockClient,
+		Endpoint: "https://test.googleapis.com",
+	}
+
+	// Make a request
+	req := &gemini.Request{
+		Contents: []gemini.Content{
+			{
+				Parts: []gemini.Part{{Text: "Hello"}},
+				Role:  "user",
+			},
+		},
+	}
+
+	ctx := context.Background()
+	res, err := model.GenerateContent(ctx, req)
+	if err != nil {
+		t.Fatalf("Failed to generate content: %v", err)
+	}
+
+	// Verify that headers were captured
+	headers := res.Header()
+	if headers == nil {
+		t.Fatalf("Expected headers to be captured, got nil")
+	}
+
+	// Check for the cost header
+	costHeader := headers.Get("Skaband-Cost-Microcents")
+	if costHeader != "123456" {
+		t.Fatalf("Expected cost header '123456', got '%s'", costHeader)
+	}
+
+	// Verify that llm.CostUSDFromResponse works with these headers
+	costUSD := llm.CostUSDFromResponse(headers)
+	expectedCost := 0.00123456 // 123456 microcents / 100,000,000
+	if costUSD != expectedCost {
+		t.Fatalf("Expected cost USD %.8f, got %.8f", expectedCost, costUSD)
+	}
+}
+
+// mockRoundTripper is a mock HTTP transport for testing
+type mockRoundTripper struct {
+	response *http.Response
+}
+
+func (m *mockRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	return m.response, nil
+}
+
+func TestHeaderCostIntegration(t *testing.T) {
+	// Create a mock HTTP client that returns a response with cost headers
+	mockClient := &http.Client{
+		Transport: &mockRoundTripper{
+			response: &http.Response{
+				StatusCode: http.StatusOK,
+				Header: http.Header{
+					"Content-Type":            []string{"application/json"},
+					"Skaband-Cost-Microcents": []string{"50000"}, // 0.5 USD
+				},
+				Body: io.NopCloser(bytes.NewBufferString(`{
+					"candidates": [{
+						"content": {
+							"parts": [{
+								"text": "Test response"
+							}]
+						}
+					}]
+				}`)),
+			},
+		},
+	}
+
+	// Create a Gem service with the mock client
+	service := &Service{
+		Model:  "gemini-test",
+		APIKey: "test-key",
+		HTTPC:  mockClient,
+		URL:    "https://test.googleapis.com",
+	}
+
+	// Create a request
+	ir := &llm.Request{
+		Messages: []llm.Message{
+			{
+				Role: llm.MessageRoleUser,
+				Content: []llm.Content{
+					{
+						Type: llm.ContentTypeText,
+						Text: "Hello",
+					},
+				},
+			},
+		},
+	}
+
+	// Make the request
+	ctx := context.Background()
+	res, err := service.Do(ctx, ir)
+	if err != nil {
+		t.Fatalf("Failed to make request: %v", err)
+	}
+
+	// Verify that the cost was captured from headers
+	expectedCost := 0.0005 // 50000 microcents / 100,000,000
+	if res.Usage.CostUSD != expectedCost {
+		t.Fatalf("Expected cost USD %.8f, got %.8f", expectedCost, res.Usage.CostUSD)
+	}
+
+	// Verify token counts are still estimated
+	if res.Usage.InputTokens == 0 {
+		t.Fatalf("Expected input tokens to be estimated, got 0")
+	}
+	if res.Usage.OutputTokens == 0 {
+		t.Fatalf("Expected output tokens to be estimated, got 0")
+	}
+}