diff --git a/src/shared/api-schemas/anthropic.ts b/src/shared/api-schemas/anthropic.ts
index fedb052..bb279d2 100644
--- a/src/shared/api-schemas/anthropic.ts
+++ b/src/shared/api-schemas/anthropic.ts
@@ -119,7 +119,8 @@ export const transformOpenAIToAnthropicChat: APIFormatTransformer<
     stream: rest.stream,
     temperature: rest.temperature,
     top_p: rest.top_p,
-    stop_sequences: typeof rest.stop === "string" ? [rest.stop] : rest.stop,
+    stop_sequences:
+      typeof rest.stop === "string" ? [rest.stop] : rest.stop || undefined,
     ...(rest.user ? { metadata: { user_id: rest.user } } : {}),
     // Anthropic supports top_k, but OpenAI does not
     // OpenAI supports frequency_penalty, presence_penalty, logit_bias, n, seed,
diff --git a/src/shared/api-schemas/openai.ts b/src/shared/api-schemas/openai.ts
index ca2edee..0f0e420 100644
--- a/src/shared/api-schemas/openai.ts
+++ b/src/shared/api-schemas/openai.ts
@@ -47,7 +47,7 @@ export const OpenAIV1ChatCompletionSchema = z
     stream: z.boolean().optional().default(false),
     stop: z
       .union([z.string().max(500), z.array(z.string().max(500))])
-      .optional(),
+      .nullish(),
     max_tokens: z.coerce
       .number()
       .int()