diff --git a/src/services/apis/openai-token-params.mjs b/src/services/apis/openai-token-params.mjs
index d5193376..c9cf9bfc 100644
--- a/src/services/apis/openai-token-params.mjs
+++ b/src/services/apis/openai-token-params.mjs
@@ -1,4 +1,4 @@
-const GPT5_CHAT_COMPLETIONS_MODEL_PATTERN = /(^|\/)gpt-5([.-]|$)/
+const GPT5_CHAT_COMPLETIONS_MODEL_PATTERN = /^gpt-5([.-]|$)/
 
 function shouldUseMaxCompletionTokens(provider, model) {
   const normalizedProvider = String(provider || '').toLowerCase()
diff --git a/tests/unit/services/apis/openai-token-params.test.mjs b/tests/unit/services/apis/openai-token-params.test.mjs
index fd64f893..8f7e7c43 100644
--- a/tests/unit/services/apis/openai-token-params.test.mjs
+++ b/tests/unit/services/apis/openai-token-params.test.mjs
@@ -8,9 +8,9 @@ test('uses max_completion_tokens for gpt-5.x chat models', () => {
   })
 })
 
-test('uses max_completion_tokens for provider-prefixed gpt-5.x models', () => {
+test('uses max_tokens for provider-prefixed gpt-5.x model names', () => {
   assert.deepEqual(getChatCompletionsTokenParams('openai', 'openai/gpt-5.2', 2048), {
-    max_completion_tokens: 2048,
+    max_tokens: 2048,
   })
 })