diff --git a/internal/runtime/executor/claude_executor.go b/internal/runtime/executor/claude_executor.go
index 7be4f41b..d426326f 100644
--- a/internal/runtime/executor/claude_executor.go
+++ b/internal/runtime/executor/claude_executor.go
@@ -35,6 +35,8 @@ type ClaudeExecutor struct {
 	cfg *config.Config
 }
 
+const claudeToolPrefix = "proxy_"
+
 func NewClaudeExecutor(cfg *config.Config) *ClaudeExecutor { return &ClaudeExecutor{cfg: cfg} }
 
 func (e *ClaudeExecutor) Identifier() string { return "claude" }
@@ -81,9 +83,14 @@ func (e *ClaudeExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, r
 	// Extract betas from body and convert to header
 	var extraBetas []string
 	extraBetas, body = extractAndRemoveBetas(body)
+	bodyForTranslation := body
+	bodyForUpstream := body
+	if isClaudeOAuthToken(apiKey) {
+		bodyForUpstream = applyClaudeToolPrefix(body, claudeToolPrefix)
+	}
 
 	url := fmt.Sprintf("%s/v1/messages?beta=true", baseURL)
-	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(bodyForUpstream))
 	if err != nil {
 		return resp, err
 	}
@@ -98,7 +105,7 @@ func (e *ClaudeExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, r
 		URL:       url,
 		Method:    http.MethodPost,
 		Headers:   httpReq.Header.Clone(),
-		Body:      body,
+		Body:      bodyForUpstream,
 		Provider:  e.Identifier(),
 		AuthID:    authID,
 		AuthLabel: authLabel,
@@ -152,8 +159,20 @@ func (e *ClaudeExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, r
 	} else {
 		reporter.publish(ctx, parseClaudeUsage(data))
 	}
+	if isClaudeOAuthToken(apiKey) {
+		data = stripClaudeToolPrefixFromResponse(data, claudeToolPrefix)
+	}
 	var param any
-	out := sdktranslator.TranslateNonStream(ctx, to, from, req.Model, bytes.Clone(opts.OriginalRequest), body, data, &param)
+	out := sdktranslator.TranslateNonStream(
+		ctx,
+		to,
+		from,
+		req.Model,
+		bytes.Clone(opts.OriginalRequest),
+		bodyForTranslation,
+		data,
+		&param,
+	)
 	resp = cliproxyexecutor.Response{Payload: []byte(out)}
 	return resp, nil
 }
@@ -193,9 +212,14 @@ func (e *ClaudeExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.A
 	// Extract betas from body and convert to header
 	var extraBetas []string
 	extraBetas, body = extractAndRemoveBetas(body)
+	bodyForTranslation := body
+	bodyForUpstream := body
+	if isClaudeOAuthToken(apiKey) {
+		bodyForUpstream = applyClaudeToolPrefix(body, claudeToolPrefix)
+	}
 
 	url := fmt.Sprintf("%s/v1/messages?beta=true", baseURL)
-	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(bodyForUpstream))
 	if err != nil {
 		return nil, err
 	}
@@ -210,7 +234,7 @@ func (e *ClaudeExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.A
 		URL:       url,
 		Method:    http.MethodPost,
 		Headers:   httpReq.Header.Clone(),
-		Body:      body,
+		Body:      bodyForUpstream,
 		Provider:  e.Identifier(),
 		AuthID:    authID,
 		AuthLabel: authLabel,
@@ -263,6 +287,9 @@ func (e *ClaudeExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.A
 				if detail, ok := parseClaudeStreamUsage(line); ok {
 					reporter.publish(ctx, detail)
 				}
+				if isClaudeOAuthToken(apiKey) {
+					line = stripClaudeToolPrefixFromStreamLine(line, claudeToolPrefix)
+				}
 				// Forward the line as-is to preserve SSE format
 				cloned := make([]byte, len(line)+1)
 				copy(cloned, line)
@@ -287,7 +314,19 @@ func (e *ClaudeExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.A
 			if detail, ok := parseClaudeStreamUsage(line); ok {
 				reporter.publish(ctx, detail)
 			}
-			chunks := sdktranslator.TranslateStream(ctx, to, from, req.Model, bytes.Clone(opts.OriginalRequest), body, bytes.Clone(line), &param)
+			if isClaudeOAuthToken(apiKey) {
+				line = stripClaudeToolPrefixFromStreamLine(line, claudeToolPrefix)
+			}
+			chunks := sdktranslator.TranslateStream(
+				ctx,
+				to,
+				from,
+				req.Model,
+				bytes.Clone(opts.OriginalRequest),
+				bodyForTranslation,
+				bytes.Clone(line),
+				&param,
+			)
 			for i := range chunks {
 				out <- cliproxyexecutor.StreamChunk{Payload: []byte(chunks[i])}
 			}
@@ -326,6 +365,9 @@ func (e *ClaudeExecutor) CountTokens(ctx context.Context, auth *cliproxyauth.Aut
 	// Extract betas from body and convert to header (for count_tokens too)
 	var extraBetas []string
 	extraBetas, body = extractAndRemoveBetas(body)
+	if isClaudeOAuthToken(apiKey) {
+		body = applyClaudeToolPrefix(body, claudeToolPrefix)
+	}
 
 	url := fmt.Sprintf("%s/v1/messages/count_tokens?beta=true", baseURL)
 	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
@@ -770,3 +812,107 @@ func checkSystemInstructions(payload []byte) []byte {
 	}
 	return payload
 }
+
+func isClaudeOAuthToken(apiKey string) bool {
+	return strings.Contains(apiKey, "sk-ant-oat")
+}
+
+func applyClaudeToolPrefix(body []byte, prefix string) []byte {
+	if prefix == "" {
+		return body
+	}
+
+	if tools := gjson.GetBytes(body, "tools"); tools.Exists() && tools.IsArray() {
+		tools.ForEach(func(index, tool gjson.Result) bool {
+			name := tool.Get("name").String()
+			if name == "" || strings.HasPrefix(name, prefix) {
+				return true
+			}
+			path := fmt.Sprintf("tools.%d.name", index.Int())
+			body, _ = sjson.SetBytes(body, path, prefix+name)
+			return true
+		})
+	}
+
+	if gjson.GetBytes(body, "tool_choice.type").String() == "tool" {
+		name := gjson.GetBytes(body, "tool_choice.name").String()
+		if name != "" && !strings.HasPrefix(name, prefix) {
+			body, _ = sjson.SetBytes(body, "tool_choice.name", prefix+name)
+		}
+	}
+
+	if messages := gjson.GetBytes(body, "messages"); messages.Exists() && messages.IsArray() {
+		messages.ForEach(func(msgIndex, msg gjson.Result) bool {
+			content := msg.Get("content")
+			if !content.Exists() || !content.IsArray() {
+				return true
+			}
+			content.ForEach(func(contentIndex, part gjson.Result) bool {
+				if part.Get("type").String() != "tool_use" {
+					return true
+				}
+				name := part.Get("name").String()
+				if name == "" || strings.HasPrefix(name, prefix) {
+					return true
+				}
+				path := fmt.Sprintf("messages.%d.content.%d.name", msgIndex.Int(), contentIndex.Int())
+				body, _ = sjson.SetBytes(body, path, prefix+name)
+				return true
+			})
+			return true
+		})
+	}
+
+	return body
+}
+
+func stripClaudeToolPrefixFromResponse(body []byte, prefix string) []byte {
+	if prefix == "" {
+		return body
+	}
+	content := gjson.GetBytes(body, "content")
+	if !content.Exists() || !content.IsArray() {
+		return body
+	}
+	content.ForEach(func(index, part gjson.Result) bool {
+		if part.Get("type").String() != "tool_use" {
+			return true
+		}
+		name := part.Get("name").String()
+		if !strings.HasPrefix(name, prefix) {
+			return true
+		}
+		path := fmt.Sprintf("content.%d.name", index.Int())
+		body, _ = sjson.SetBytes(body, path, strings.TrimPrefix(name, prefix))
+		return true
+	})
+	return body
+}
+
+func stripClaudeToolPrefixFromStreamLine(line []byte, prefix string) []byte {
+	if prefix == "" {
+		return line
+	}
+	payload := jsonPayload(line)
+	if len(payload) == 0 || !gjson.ValidBytes(payload) {
+		return line
+	}
+	contentBlock := gjson.GetBytes(payload, "content_block")
+	if !contentBlock.Exists() || contentBlock.Get("type").String() != "tool_use" {
+		return line
+	}
+	name := contentBlock.Get("name").String()
+	if !strings.HasPrefix(name, prefix) {
+		return line
+	}
+	updated, err := sjson.SetBytes(payload, "content_block.name", strings.TrimPrefix(name, prefix))
+	if err != nil {
+		return line
+	}
+
+	trimmed := bytes.TrimSpace(line)
+	if bytes.HasPrefix(trimmed, []byte("data:")) {
+		return append([]byte("data: "), updated...)
+	}
+	return updated
+}
diff --git a/internal/runtime/executor/claude_executor_test.go b/internal/runtime/executor/claude_executor_test.go
new file mode 100644
index 00000000..05f5b60c
--- /dev/null
+++ b/internal/runtime/executor/claude_executor_test.go
@@ -0,0 +1,51 @@
+package executor
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestApplyClaudeToolPrefix(t *testing.T) {
+	input := []byte(`{"tools":[{"name":"alpha"},{"name":"proxy_bravo"}],"tool_choice":{"type":"tool","name":"charlie"},"messages":[{"role":"assistant","content":[{"type":"tool_use","name":"delta","id":"t1","input":{}}]}]}`)
+	out := applyClaudeToolPrefix(input, "proxy_")
+
+	if got := gjson.GetBytes(out, "tools.0.name").String(); got != "proxy_alpha" {
+		t.Fatalf("tools.0.name = %q, want %q", got, "proxy_alpha")
+	}
+	if got := gjson.GetBytes(out, "tools.1.name").String(); got != "proxy_bravo" {
+		t.Fatalf("tools.1.name = %q, want %q", got, "proxy_bravo")
+	}
+	if got := gjson.GetBytes(out, "tool_choice.name").String(); got != "proxy_charlie" {
+		t.Fatalf("tool_choice.name = %q, want %q", got, "proxy_charlie")
+	}
+	if got := gjson.GetBytes(out, "messages.0.content.0.name").String(); got != "proxy_delta" {
+		t.Fatalf("messages.0.content.0.name = %q, want %q", got, "proxy_delta")
+	}
+}
+
+func TestStripClaudeToolPrefixFromResponse(t *testing.T) {
+	input := []byte(`{"content":[{"type":"tool_use","name":"proxy_alpha","id":"t1","input":{}},{"type":"tool_use","name":"bravo","id":"t2","input":{}}]}`)
+	out := stripClaudeToolPrefixFromResponse(input, "proxy_")
+
+	if got := gjson.GetBytes(out, "content.0.name").String(); got != "alpha" {
+		t.Fatalf("content.0.name = %q, want %q", got, "alpha")
+	}
+	if got := gjson.GetBytes(out, "content.1.name").String(); got != "bravo" {
+		t.Fatalf("content.1.name = %q, want %q", got, "bravo")
+	}
+}
+
+func TestStripClaudeToolPrefixFromStreamLine(t *testing.T) {
+	line := []byte(`data: {"type":"content_block_start","content_block":{"type":"tool_use","name":"proxy_alpha","id":"t1"},"index":0}`)
+	out := stripClaudeToolPrefixFromStreamLine(line, "proxy_")
+
+	payload := bytes.TrimSpace(out)
+	if bytes.HasPrefix(payload, []byte("data:")) {
+		payload = bytes.TrimSpace(payload[len("data:"):])
+	}
+	if got := gjson.GetBytes(payload, "content_block.name").String(); got != "alpha" {
+		t.Fatalf("content_block.name = %q, want %q", got, "alpha")
+	}
+}