diff --git a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
index 85b28b8b..e9a62426 100644
--- a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
+++ b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
@@ -34,6 +34,11 @@ func ConvertOpenAIRequestToAntigravity(modelName string, inputRawJSON []byte, _
 	// Model
 	out, _ = sjson.SetBytes(out, "model", modelName)
 
+	// Let user-provided generationConfig pass through
+	if genConfig := gjson.GetBytes(rawJSON, "generationConfig"); genConfig.Exists() {
+		out, _ = sjson.SetRawBytes(out, "request.generationConfig", []byte(genConfig.Raw))
+	}
+
 	// Apply thinking configuration: convert OpenAI reasoning_effort to Gemini CLI thinkingConfig.
 	// Inline translation-only mapping; capability checks happen later in ApplyThinking.
 	re := gjson.GetBytes(rawJSON, "reasoning_effort")
diff --git a/internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go b/internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go
index 53da71f4..b0a6bddd 100644
--- a/internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go
+++ b/internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go
@@ -34,6 +34,11 @@ func ConvertOpenAIRequestToGeminiCLI(modelName string, inputRawJSON []byte, _ bo
 	// Model
 	out, _ = sjson.SetBytes(out, "model", modelName)
 
+	// Let user-provided generationConfig pass through
+	if genConfig := gjson.GetBytes(rawJSON, "generationConfig"); genConfig.Exists() {
+		out, _ = sjson.SetRawBytes(out, "request.generationConfig", []byte(genConfig.Raw))
+	}
+
 	// Apply thinking configuration: convert OpenAI reasoning_effort to Gemini CLI thinkingConfig.
 	// Inline translation-only mapping; capability checks happen later in ApplyThinking.
 	re := gjson.GetBytes(rawJSON, "reasoning_effort")
diff --git a/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go b/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
index 5de35681..f18f45be 100644
--- a/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
+++ b/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
@@ -34,6 +34,11 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 	// Model
 	out, _ = sjson.SetBytes(out, "model", modelName)
 
+	// Let user-provided generationConfig pass through
+	if genConfig := gjson.GetBytes(rawJSON, "generationConfig"); genConfig.Exists() {
+		out, _ = sjson.SetRawBytes(out, "generationConfig", []byte(genConfig.Raw))
+	}
+
 	// Apply thinking configuration: convert OpenAI reasoning_effort to Gemini thinkingConfig.
 	// Inline translation-only mapping; capability checks happen later in ApplyThinking.
 	re := gjson.GetBytes(rawJSON, "reasoning_effort")