diff --git a/internal/llm/anthropic.go b/internal/llm/anthropic.go
new file mode 100644
index 0000000..720d101
--- /dev/null
+++ b/internal/llm/anthropic.go
@@ -0,0 +1,91 @@
+package llm
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+)
+
+type anthropicClient struct {
+	http      *http.Client
+	base      string
+	key       string
+	model     string
+	maxTokens int
+}
+
+func (c *anthropicClient) Vision(ctx context.Context, prompt string, images []Image, opts Options) (string, error) {
+	content := []map[string]any{}
+	for _, img := range images {
+		content = append(content, map[string]any{
+			"type": "image",
+			"source": map[string]any{
+				"type":       "base64",
+				"media_type": img.MediaType,
+				"data":       base64.StdEncoding.EncodeToString(img.Data),
+			},
+		})
+	}
+	content = append(content, map[string]any{"type": "text", "text": prompt})
+
+	model := c.model
+	if opts.Model != "" {
+		model = opts.Model
+	}
+	maxTok := c.maxTokens
+	if opts.MaxTokens > 0 {
+		maxTok = opts.MaxTokens
+	}
+	// NOTE: temperature/top_p are intentionally omitted — Opus 4.x rejects them (HTTP 400).
+	reqBody := map[string]any{
+		"model":      model,
+		"max_tokens": maxTok,
+		"messages":   []map[string]any{{"role": "user", "content": content}},
+	}
+	b, err := json.Marshal(reqBody)
+	if err != nil {
+		return "", err
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.base+"/v1/messages", bytes.NewReader(b))
+	if err != nil {
+		return "", err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("x-api-key", c.key)
+	req.Header.Set("anthropic-version", "2023-06-01")
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer func() { _ = resp.Body.Close() }()
+	raw, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", err
+	}
+	if resp.StatusCode >= 300 {
+		return "", fmt.Errorf("anthropic HTTP %d: %s", resp.StatusCode, string(raw))
+	}
+	var out struct {
+		Content []struct {
+			Type string `json:"type"`
+			Text string `json:"text"`
+		} `json:"content"`
+	}
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return "", err
+	}
+	for _, blk := range out.Content {
+		if blk.Type == "text" {
+			return blk.Text, nil
+		}
+	}
+	return "", fmt.Errorf("anthropic: no text block in response")
+}
+
+func (c *anthropicClient) Transcribe(_ context.Context, _ []byte, _ string, _ Options) (string, error) {
+	return "", ErrUnsupported{Provider: "anthropic"}
+}
diff --git a/internal/llm/anthropic_test.go b/internal/llm/anthropic_test.go
new file mode 100644
index 0000000..5667b48
--- /dev/null
+++ b/internal/llm/anthropic_test.go
@@ -0,0 +1,49 @@
+package llm
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestAnthropicVision(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/v1/messages" {
+			t.Errorf("path %s", r.URL.Path)
+		}
+		if r.Header.Get("x-api-key") != "key" || r.Header.Get("anthropic-version") != "2023-06-01" {
+			t.Errorf("headers %v", r.Header)
+		}
+		raw, _ := io.ReadAll(r.Body)
+		if strings.Contains(string(raw), "temperature") {
+			t.Errorf("temperature must NOT be sent to anthropic: %s", raw)
+		}
+		if !strings.Contains(string(raw), `"type":"base64"`) {
+			t.Errorf("image block missing: %s", raw)
+		}
+		_, _ = io.WriteString(w, `{"content":[{"type":"text","text":"crosswalk"}]}`)
+	}))
+	defer srv.Close()
+
+	c := &anthropicClient{http: &http.Client{Timeout: 5 * time.Second}, base: srv.URL, key: "key", model: "claude-opus-4-8", maxTokens: 100}
+	got, err := c.Vision(context.Background(), "which tiles", []Image{{MediaType: "image/png", Data: []byte{2}}}, Options{Temperature: 0.7})
+	if err != nil || got != "crosswalk" {
+		t.Fatalf("got %q err %v", got, err)
+	}
+	_ = json.Marshal // keep import
+}
+
+func TestAnthropicTranscribeUnsupported(t *testing.T) {
+	c := &anthropicClient{model: "claude-opus-4-8"}
+	_, err := c.Transcribe(context.Background(), []byte{1}, "a.mp3", Options{})
+	var u ErrUnsupported
+	if !errors.As(err, &u) {
+		t.Fatalf("want ErrUnsupported, got %v", err)
+	}
+}