OpenCode Go: kimi-k3, kimi-k2.6, kimi-k2.7-code, glm-5.2, grok-4.5, qwen3.7-max, hy3-preview all fail with 'Upstream request failed' — non-standard 'mcp'/'system' fields rejected by strict provider validators #37771

Summary

7 of the newest OpenCode Go (zen/go/v1) models fail on every call with a generic Error from provider (Console Go): Upstream request failed, wrapped from an underlying HTTP 400. Confirmed via direct capture of the CLI's real outbound request (bypassing opencode's swallowed error), the upstream provider returns:

"Error from provider: 2 request validation errors: Extra inputs are not permitted, field: 'mcp', value: [...]; Extra inputs are not permitted, field: 'system', value: '...'"

Affected models (confirmed via opencode-go)

• kimi-k3
• kimi-k2.6
• kimi-k2.7-code
• glm-5.2
• grok-4.5
• qwen3.7-max
• hy3-preview

Working models on the same provider (glm-5.1, mimo-v2.5/-pro, minimax-m2.7/m3, qwen3.6-plus/3.7-plus, deepseek-v4-pro/flash) are unaffected — their backing providers apparently tolerate unknown top-level fields; the affected models' backends (Moonshot/Fireworks-routed Kimi, and presumably similar strict validators for the others) reject the request outright per Pydantic-style strict schema validation.

Root cause

opencode's request body to zen/go/v1/chat/completions includes two non-standard top-level fields not part of the OpenAI Chat Completions spec:

• "mcp": ["context7","savecontext","serena",...] — array of active MCP provider names
• "system": "<full system prompt string>" (in addition to / instead of a messages[].role=system entry)

These are presumably intended as opencode-internal metadata or a legacy field format, but get forwarded verbatim to the upstream Console Go endpoint instead of being stripped for providers with strict input validation.

Reproduction

1. opencode run -m opencode-go/kimi-k2.6 "hello" (or any of the affected models above)
2. Fails instantly (~1.2s) with Error from provider (Console Go): Upstream request failed
3. Direct curl replay of the exact captured request body against https://opencode.ai/zen/go/v1/chat/completions reproduces the 400 with the full validation error shown above.
4. Removing the mcp and system fields from the payload (keeping messages with a system-role entry instead) is expected to fix it — not yet tested with fields fully removed, but the validator error names them explicitly as the two rejected fields.

Version

opencode 1.18.3 (bun 1.3.14), installed via brew

Related

• KIMI K2.6 showing error in Opencode GO #27054 (KIMI K2.6 showing error in Opencode GO — JSON Schema $defs mismatch) — different underlying cause (tool schema shape) but same symptom class (Kimi/Moonshot strict-validator rejecting opencode's request shape) and same generic wrapped error message.
• JSON Schema validation fails on empty tool parameters {} with Kimi K2.5 (strict mode error) #11357 (JSON Schema validation fails on empty tool parameters with Kimi K2.5)

Multiple users independently hit this in the last 1-2 days on Reddit (r/opencodeCLI, r/opencode) and X, all reporting Kimi K3 "unusable" on Go subscriptions with the identical error string.