diff --git a/src/resources/chat/completions/completions.ts b/src/resources/chat/completions/completions.ts
index 80e426bdf..1600fabaa 100644
--- a/src/resources/chat/completions/completions.ts
+++ b/src/resources/chat/completions/completions.ts
@@ -1644,7 +1644,7 @@ export interface ChatCompletionCreateParamsBase {
    * of 24 hours.
    * [Learn more](https://platform.openai.com/docs/guides/prompt-caching#prompt-cache-retention).
    */
-  prompt_cache_retention?: 'in-memory' | '24h' | null;
+  prompt_cache_retention?: 'in_memory' | '24h' | null;
 
   /**
    * Constrains effort on reasoning for
diff --git a/src/resources/responses/responses.ts b/src/resources/responses/responses.ts
index c60c2cce9..d15fd8216 100644
--- a/src/resources/responses/responses.ts
+++ b/src/resources/responses/responses.ts
@@ -590,7 +590,7 @@ export interface Response {
    * of 24 hours.
    * [Learn more](https://platform.openai.com/docs/guides/prompt-caching#prompt-cache-retention).
    */
-  prompt_cache_retention?: 'in-memory' | '24h' | null;
+  prompt_cache_retention?: 'in_memory' | '24h' | null;
 
   /**
    * **gpt-5 and o-series models only**
@@ -6148,7 +6148,7 @@ export interface ResponseCreateParamsBase {
    * of 24 hours.
    * [Learn more](https://platform.openai.com/docs/guides/prompt-caching#prompt-cache-retention).
    */
-  prompt_cache_retention?: 'in-memory' | '24h' | null;
+  prompt_cache_retention?: 'in_memory' | '24h' | null;
 
   /**
    * **gpt-5 and o-series models only**
diff --git a/tests/api-resources/chat/completions/completions.test.ts b/tests/api-resources/chat/completions/completions.test.ts
index ec4694b34..c17eb0fd1 100644
--- a/tests/api-resources/chat/completions/completions.test.ts
+++ b/tests/api-resources/chat/completions/completions.test.ts
@@ -41,7 +41,7 @@ describe('resource completions', () => {
       prediction: { content: 'string', type: 'content' },
       presence_penalty: -2,
       prompt_cache_key: 'prompt-cache-key-1234',
-      prompt_cache_retention: 'in-memory',
+      prompt_cache_retention: 'in_memory',
       reasoning_effort: 'none',
       response_format: { type: 'text' },
       safety_identifier: 'safety-identifier-1234',