silent fallback to opus 4.8 or gpt 5.3 codex

[mtahasylmz]

Hey team,

Box silently uses some predefined models when some other model is chosen with OpenRouter as the provider.

Go to the console, create a box with claude code harness, choose, say, DeepSeek V4 Flash from OpenRouter. It will say that it successfully created the box, yet Claude Code falls back to Opus 4.8. If you do it with Codex, it will silently fallback to GPT-5.3-codex.

I realized this when i used my own OpenRouter key, and its logs reported me different models than i used and my credit is gone way faster. I thought it is because of BYOK but the following image is a box with Upstash Managed model provider.

see that console claims it to be deepseek and local logs tell otherwise.

let me know if i am missing sth.

Thanks

[mtahasylmz]

I do not think it is related only to OpenRouter btw, i think this is because of a local model list in the source code since these fallback models were the latest models when box was first introduced. Below is a concise report from my agent. I know that this is not related to this SDK repo but i think this is the best way to reach out.

---

Bug: Claude Code silently ignores selected OpenRouter model

Using @upstash/box@0.7.0 with an Upstash-managed key:

await Box.create({
  runtime: "node",
  agent: {
    harness: Agent.ClaudeCode,
    model: "openrouter/deepseek/deepseek-r1",
    apiKey: BoxApiKey.UpstashKey,
  },
});

The Box metadata records the requested DeepSeek model, but Claude Code’s session JSONL records:

anthropic/claude-opus-4.8

Reproduced with both DeepSeek R1—an official OpenRouterModel value—and DeepSeek V4 Flash. It also reproduces through the raw /v2/box REST API, without the SDK.

Expected: execute the selected model, or reject unsupported combinations before inference.

Actual: silently executes and bills an unrelated Opus model.

Example retained Boxes:

• romantic-mongrel-63475 — DeepSeek R1
• sterling-gorilla-09237 — DeepSeek V4 Flash

[mtahasylmz]

By the way, apart from this issue, it would be great if we were able to see which harness it is when we are inspecting a specific box on console. It is visible on the boxes list, yet when i click on one of them, there is no indicator stating which harness it is.