diff --git a/open-sse/translator/concerns/finishReasonMap.js b/open-sse/translator/concerns/finishReasonMap.js
new file mode 100644
index 00000000..62d5a4ce
--- /dev/null
+++ b/open-sse/translator/concerns/finishReasonMap.js
@@ -0,0 +1,43 @@
+// Concern #6: finish_reason / stop_reason mapping.
+// One entry per direction; switch by special format, default handles common providers.
+
+// upstream finish/stop reason → OpenAI finish_reason
+export function toOpenAIFinish(reason, format) {
+  switch (format) {
+    case "claude":
+      switch (reason) {
+        case "end_turn": return "stop";
+        case "max_tokens": return "length";
+        case "tool_use": return "tool_calls";
+        case "stop_sequence": return "stop";
+        default: return "stop";
+      }
+    case "commandcode":
+      switch (reason) {
+        case "stop": return "stop";
+        case "length": return "length";
+        case "tool-calls":
+        case "tool_use": return "tool_calls";
+        case "content-filter": return "content_filter";
+        case "error": return "stop";
+        default: return reason || "stop";
+      }
+    default:
+      return reason || "stop";
+  }
+}
+
+// OpenAI finish_reason → upstream stop reason
+export function fromOpenAIFinish(reason, format) {
+  switch (format) {
+    case "claude":
+      switch (reason) {
+        case "stop": return "end_turn";
+        case "length": return "max_tokens";
+        case "tool_calls": return "tool_use";
+        default: return "end_turn";
+      }
+    default:
+      return reason;
+  }
+}
diff --git a/open-sse/translator/response/claude-to-openai.js b/open-sse/translator/response/claude-to-openai.js
index ff5ccafe..b13ba8e5 100644
--- a/open-sse/translator/response/claude-to-openai.js
+++ b/open-sse/translator/response/claude-to-openai.js
@@ -3,6 +3,7 @@ import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
 import { buildUsage } from "../helpers/usageHelper.js";
 import { reasoningDelta } from "../helpers/reasoningHelper.js";
+import { toOpenAIFinish } from "../concerns/finishReasonMap.js";
 
 // Create OpenAI chunk helper
 function createChunk(state, delta, finishReason = null) {
@@ -164,16 +165,7 @@ export function claudeToOpenAIResponse(chunk, state) {
   return results.length > 0 ? results : null;
 }
 
-// Convert Claude stop_reason to OpenAI finish_reason
-function convertStopReason(reason) {
-  switch (reason) {
-    case "end_turn": return "stop";
-    case "max_tokens": return "length";
-    case "tool_use": return "tool_calls";
-    case "stop_sequence": return "stop";
-    default: return "stop";
-  }
-}
+const convertStopReason = (reason) => toOpenAIFinish(reason, "claude");
 
 // Register
 register(FORMATS.CLAUDE, FORMATS.OPENAI, null, claudeToOpenAIResponse);
diff --git a/open-sse/translator/response/commandcode-to-openai.js b/open-sse/translator/response/commandcode-to-openai.js
index 77483955..a11d800d 100644
--- a/open-sse/translator/response/commandcode-to-openai.js
+++ b/open-sse/translator/response/commandcode-to-openai.js
@@ -19,6 +19,7 @@ import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
 import { reasoningDelta } from "../helpers/reasoningHelper.js";
+import { toOpenAIFinish } from "../concerns/finishReasonMap.js";
 
 function ensureState(state, model) {
   if (!state.responseId) {
@@ -43,17 +44,7 @@ function makeChunk(state, delta, finishReason = null) {
   );
 }
 
-function mapFinishReason(reason) {
-  switch (reason) {
-    case "stop": return "stop";
-    case "length": return "length";
-    case "tool-calls":
-    case "tool_use": return "tool_calls";
-    case "content-filter": return "content_filter";
-    case "error": return "stop";
-    default: return reason || "stop";
-  }
-}
+const mapFinishReason = (reason) => toOpenAIFinish(reason, "commandcode");
 
 export function convertCommandCodeToOpenAI(chunk, state) {
   if (!chunk) return null;
diff --git a/open-sse/translator/response/openai-to-claude.js b/open-sse/translator/response/openai-to-claude.js
index 6a46551d..f2e20e84 100644
--- a/open-sse/translator/response/openai-to-claude.js
+++ b/open-sse/translator/response/openai-to-claude.js
@@ -1,5 +1,6 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
+import { fromOpenAIFinish } from "../concerns/finishReasonMap.js";
 
 // Prefix for Claude OAuth tool names (must match request translator)
 const CLAUDE_OAUTH_TOOL_PREFIX = "proxy_";
@@ -252,15 +253,7 @@ export function openaiToClaudeResponse(chunk, state) {
   return results.length > 0 ? results : null;
 }
 
-// Convert OpenAI finish_reason to Claude stop_reason
-function convertFinishReason(reason) {
-  switch (reason) {
-    case "stop": return "end_turn";
-    case "length": return "max_tokens";
-    case "tool_calls": return "tool_use";
-    default: return "end_turn";
-  }
-}
+const convertFinishReason = (reason) => fromOpenAIFinish(reason, "claude");
 
 // Register
 register(FORMATS.OPENAI, FORMATS.CLAUDE, null, openaiToClaudeResponse);