# [Additive] OpenAI: 4 new response fields

> Source: <https://driftwatch.et/apis/openai#cmw1bkbvm000k0dwsk2ve9el7-fields>
> Published: 2026-11-03 22:29:31+00:00

[OpenAI](https://driftwatch.et/apis/openai)2 breaking4 additive

- Breakingdirection flip: their tools call this safe[prompt_cache_options is no longer accepted](https://driftwatch.et/changes/openai-2026-11-03-7094f95d)Usually ignored rather than rejected, so the call succeeds and does something subtly different. 2 places: CreateModelResponseProperties.prompt_cache_options, BetaCreateModelResponseProperties.prompt_cache_options## Code that breaks

```
await client.post("/…", {
  // prompt_cache_options is now ignored, not rejected
  prompt_cache_options: value,
});
```

- Breakingdirection flip: their tools call this safe[value can now return "max_output_tokens"](https://driftwatch.et/changes/openai-2026-11-03-2cc3309f)Producer-side tools call this additive. It breaks exhaustive switches, strict parsers and generated client enums. SessionTurnErrorCodeResource · reachable from 6 operations## Code that breaks

```
switch (response) {
  // existing branches …
  // no branch for "max_output_tokens"
  default:
    throw new Error("unexpected value");
}
```

## 4 new response fields

- ResponseUsage.input_tokens_details.cache_write_tokens_details
- BetaResponseUsage.input_tokens_details.cache_write_tokens_details
- BetaResponse.usage.input_tokens_details.cache_write_tokens_details
- Response.usage.input_tokens_details.cache_write_tokens_details