[Bug] OpenCode Go: some models return `403 Forbidden: {"model":"<model>"}` while others work (subscription active, limits not reached)

Description

Using the OpenCode Go provider (opencode-go) with an active subscription and API key, certain models fail with AI_APICallError: Forbidden. The error body echoes the requested model id:

Forbidden: {"model":"mimo-v2.5"}

The subscription is active and usage limits are not exhausted. Other Go models work fine with the same key.

Environment

• opencode version: 1.18.11
• OS: Windows
• Provider: opencode-go (OpenCode Go subscription)
• Key type: sk-... API key from the Zen console

Models affected

With the same API key, direct requests to https://opencode.ai/zen/go/v1/chat/completions:

Model	Status
mimo-v2.5	403 {"model":"mimo-v2.5"}
mimo-v2.5-pro	403 {"model":"mimo-v2.5-pro"}
hy3	403 {"model":"hy3"}
gpt-5.6-luna (via /responses)	403
deepseek-v4-flash	200 OK
deepseek-v4-pro	200 OK
glm-5.2	200 OK
glm-5.1	200 OK
kimi-k3	200 OK
kimi-k2.7-code	200 OK
qwen3.8-max	200 OK
grok-4.5	500 (separate server error)

The affected models are listed in the gateway's catalog (GET https://opencode.ai/zen/go/v1/models includes mimo-v2.5, mimo-v2.5-pro, hy3, gpt-5.6-luna), so this is an authorization/entitlement decision, not "unknown model".

Repro (no opencode needed)

POST https://opencode.ai/zen/go/v1/chat/completions
Authorization: Bearer <opencode-go-api-key>
Content-Type: application/json

{ "model": "mimo-v2.5",
  "messages": [{ "role": "user", "content": "hi" }],
  "max_tokens": 3 }

Response:

HTTP/1.1 403 Forbidden
Content-Type: application/json

{"model":"mimo-v2.5"}

Not user-agent dependent (tested opencode, opencode/1.18.11, Mozilla/5.0 ..., curl/8.0, Python-urllib/3.11 — all return the same 403 body for the affected models; only Python-urllib triggers the separate Cloudflare 1010 block).

Expected behavior

All models advertised for the Go subscription (including mimo-v2.5) should be usable while the subscription is active and limits are not reached.

Additional context

• A related issue (#39374) describes a Python-urllib user-agent 403 — this is a different case: here the 403 is model-specific and independent of user-agent.
• Docs page lists MiMo-V2.5 as a current Go model: https://opencode.ai/docs/go/

Plugins

No response

OpenCode version

No response

Steps to reproduce

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Screenshot and/or share link

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Operating System

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Terminal

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