[Windows] @ai-sdk/openai-compatible cannot connect to localhost:9877 — Bun fetch fails for 127.0.0.1 while Node fetch works (Unable to connect. Is the computer able to access the url?)

Summary

On Windows, opencode's embedded Bun runtime cannot connect to a localhost @ai-sdk/openai-compatible provider at http://127.0.0.1:9877/v1. Every request fails with AI_APICallError: Cannot connect to API: Unable to connect. Is the computer able to access the url?. The same URL is reachable from Node.js fetch(), PowerShell Invoke-WebRequest, and curl on the same machine — so this is an opencode/Bun runtime issue, not a network or proxy issue.

This appears related to #28418 (@ai-sdk/openai-compatible fails to connect to LAN addresses) and #37043 (opencode ignores NO_PROXY), but this reproduces on plain 127.0.0.1 with no HTTP_PROXY/HTTPS_PROXY env vars set.

Environment

• opencode: v1.18.4 (installed via npm i -g opencode-ai, binary at D:\node_global\opencode.ps1)
• OS: Windows 11, PowerShell 5.1
• Node: v22.19.0
• Bun: installed at D:\node_global\bun.ps1 (bundled runtime used by opencode)
• Provider: @ai-sdk/openai-compatible pointing at a local reverse proxy (commandcode-api-proxy v0.3.0) on http://127.0.0.1:9877/v1

Reproduction

Config (~/.config/opencode/opencode.jsonc)

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "commandcode": {
      "npm": "@ai-sdk/openai-compatible",
      "name": "Command Code",
      "options": {
        "baseURL": "http://127.0.0.1:9877/v1",
        "apiKey": "proxy-managed"
      },
      "models": {
        "deepseek-v4-pro": { "name": "DeepSeek V4 Pro" }
      }
    }
  }
}

Steps

1. Start a local OpenAI-compatible server on 127.0.0.1:9877 (any will do — I used commandcode-api-proxy).
2. Launch opencode, select the commandcode provider / deepseek-v4-pro model.
3. Send any message.

Actual

opencode retries 3× then fails:

AI_APICallError: Cannot connect to API: Unable to connect. Is the computer able to access the url?
(cause: Error: Unable to connect. Is the computer able to access the url?)

Full log (~/.local/share/opencode/log/opencode.log):

timestamp=2026-07-21T15:34:23.959Z level=ERROR message="stream error" providerID=commandcode modelID=deepseek-v4-pro error.error="AI_APICallError: Cannot connect to API: Unable to connect. Is the computer able to access the url? (cause: Error: Unable to connect. Is the computer able to access the url?)"
timestamp=2026-07-21T15:34:29.384Z level=ERROR message="stream error" providerID=commandcode modelID=deepseek-v4-pro error.error="AI_RetryError: Failed after 3 attempts. Last error: Cannot connect to API: Unable to connect. Is the computer able to access the url?"

Notably, https://models.dev/api.json also fails with the exact same error — so the Bun runtime cannot reach any URL, not just localhost:

timestamp=2026-07-21T15:34:05.945Z level=ERROR message="Failed to fetch models.dev" cause="Cause([Fail(HttpClientError: Transport error (GET https://models.dev/api.json) (cause: Error: Unable to connect. Is the computer able to access the url?))])"

Expected

opencode connects to http://127.0.0.1:9877/v1/chat/completions and returns a response.

Proof the endpoint is reachable (same machine, same moment)

Node.js fetch() — works

const r = await fetch("http://127.0.0.1:9877/health");
console.log(r.status, await r.text());
// → 200 {"status":"ok","version":"0.1.0"}

PowerShell Invoke-WebRequest — works

Invoke-WebRequest "http://127.0.0.1:9877/health" -UseBasicParsing
# → 200 {"status":"ok","version":"0.1.0"}

$body = '{"model":"deepseek/deepseek-v4-flash","messages":[{"role":"user","content":"hi"}],"stream":false,"max_tokens":20}'
Invoke-WebRequest "http://127.0.0.1:9877/v1/chat/completions" -Method POST -Headers @{Authorization="Bearer proxy-managed";"Content-Type"="application/json"} -Body $body
# → 200, valid chat completion returned

Port is listening

Get-NetTCPConnection -LocalPort 9877
# → 127.0.0.1:9877  Listen  (OwningProcess confirmed)

What I've already tried

• No proxy env vars set: HTTP_PROXY, HTTPS_PROXY, NO_PROXY are all unset (verified via Get-ChildItem env:).
• Plugin that sets init.proxy for non-local URLs only: I have a proxy.ts plugin that routes non-local fetches through a local HTTP proxy at 127.0.0.1:60230, but it explicitly skips localhost/127.0.0.1/::1. Removing the plugin entirely does not fix the issue.
• Both opencode.json and opencode.jsonc: consolidated to a single opencode.jsonc — no change.
• Different localhost ports: tried 8787 (got EACCES — Windows reserved range), 9877, 9876 — all fail the same way in opencode.
• 127.0.0.1 vs localhost: not yet tested swapping, but #28418 reports hostname also fails.

Hypothesis

opencode's embedded Bun runtime fetch() is broken for outbound HTTP on this Windows environment — it fails for both 127.0.0.1 (local proxy) and https://models.dev (public HTTPS). Node.js fetch() on the same machine works for both. This smells like a Bun-on-Windows socket/transport bug rather than a provider config issue, possibly the same class as #28418 but broader (affects public URLs too, not just LAN).

Questions / Workarounds sought

1. Is there a way to force opencode to use Node's fetch instead of Bun's for provider calls?
2. Any known Windows-specific Bun fetch workaround (env var, config flag)?
3. Could this be related to the bundled Bun version? If so, is there a way to override it?

Happy to run any additional diagnostics the maintainers need.