[FEATURE]: Support Responses API for deepseek-v4-flash on opencode-go

[YiRan0]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

DeepSeek's formal deepseek-v4-flash-0731 checkpoint (released Jul 31, 2026) natively supports the OpenAI Responses API (https://api.deepseek.com → /v1/responses). However, opencode-go only serves deepseek-v4-flash via /v1/chat/completions:

• POST https://opencode.ai/zen/go/v1/responses with deepseek-v4-flash → HTTP 400: Error from provider (Console Go): Upstream request failed
• The same endpoint works fine for GPT-5.x models (e.g. gpt-5.6-luna)
• The same request succeeds against DeepSeek's official Responses API

This blocks Codex-style clients (which speak the Responses protocol) from using DeepSeek V4 Flash through opencode-go.

Proposed behavior:

1. Switch deepseek-v4-flash upstream to the 0731 checkpoint that supports Responses API natively.
2. Forward /v1/responses requests for deepseek-v4-flash to the upstream Responses endpoint (like GPT-5.x models).
3. Keep /v1/chat/completions working for backwards compatibility.

Additional context:

• DeepSeek official docs: https://api-docs.deepseek.com/zh-cn/guides/responses_api
• Related: DeepSeek V4 Flash formal version (0731) — is it already live on OpenCode Go/Zen? #39823 (is the 0731 checkpoint live?), [Zen] AuthError: "Request blocked by upstream provider" — all Zen models broken, account recreated #39827 (Go gateway outage today)

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: add Responses API support for Go service #23655: [FEATURE]: add Responses API support for Go service — requests the same /v1/responses endpoint for the Go service, covering all Go service models. Your request is more specifically scoped to deepseek-v4-flash and the 0731 checkpoint, but the underlying ask overlaps significantly.

[LuckyPro-X]

👍

[lesacar]

for your 3rd point, there should also be a way to tell which API you're using (clear distinction saying you're using Completions or you're using responses) , since I've only been using deepseek, I don't know how to tell if "retained reasoning" is turned on in opencode which requires the new responses api

[cubelitblade]

Makes sense for the free version on Zen too — and since OpenCode GPT is Responses-only, maybe just keep DeepSeek the same for consistency?

[JINGMINGRUO]

Adding my support here. DeepSeek's official API already natively supports the Responses API for deepseek-v4-flash (POST https://api.deepseek.com/v1/responses works with this model), so supporting it on opencode-go should be straightforward: forward /v1/responses requests for DeepSeek V4 Flash to the official upstream Responses endpoint, the same way GPT-5.x models are already handled. Since opencode-go already serves /v1/responses for the GPT models, adding DeepSeek V4 Flash would keep the behavior consistent and let Codex-style clients use DeepSeek through opencode-go. I hope the team can prioritize this — it is just a small mapping on top of an officially supported upstream.

[LeaningLearner]

So, does that mean Codex still cannot use DeepSeek V4 Flash through OpenCode Go?

[JINGMINGRUO]

Short answer: not yet, but a fix is ready and just needs to be merged.

The problem: OpenCode Go currently serves DeepSeek V4 Flash through a chat-completions upstream and converts that stream into a Responses-API stream. The conversion was missing the lifecycle events Codex relies on (response.created, response.output_item.added, response.content_part.added, response.output_item.done), so Codex turns hang or fail.

PR #40210 fixes that conversion, so Codex should be able to use DeepSeek V4 Flash through OpenCode Go once it is merged and deployed.

In the long run, the more solid fix is native support: forward /v1/responses for deepseek-v4-flash directly to DeepSeek's official Responses endpoint, like OpenCode Go already does for GPT models, instead of translating from chat completions. That is what #39829 / #23655 ask for.

If this affects you too, a thumbs-up or a short comment on #40210 would help it get reviewed and merged.