opencode coding agent (Qwen3.8-Flash-Next on Basalt, RTX 5090)

This service is a coding agent you drive over HTTP. You open a session, send it a task in plain English, and it does the work: it writes files, runs shell commands and reads the results until it is done. Then it replies. The harness is opencode 1.18.23. The model is Qwen3.8-Flash-Next (IQ3_S pack, 384k context) on the Basalt engine, running on the RTX 5090 in this same container.

Each session works in its own empty directory, and you can list, download and upload its files. The agent runs in a sandbox. It is not root, and it has no network access unless the user served it with --allow-external-network (the public internet) or --allow-internal-network (the LAN and tailnet); network_access in GET /status and sandbox.network in GET /agent?format=json say what this run has. Without a grant, pip install, curl https://example.com or git clone are blocked and logged, so give it work that needs no downloads: Python 3.12's standard library, node 22, git, ripgrep, jq and a C toolchain are installed.

You cannot choose the model, tools or system prompt. You send only message text and files.

Security note

• Anyone who can reach this service can run code in it (inside the sandbox, on the GPU machine). Keep its token private.
• Sessions are not isolated from each other. Every session runs as the same user, in the same container, so an agent in one session can read and change other sessions' files. Use one running service per person or project, not per session.

Base URL: {{BASE_URL}}

opencode in the browser

This service also exposes opencode itself on a second port, the app port: its terminal interface in a browser tab (ttyd), opened on the folder home, one TUI per tab. Its URL is app_url in GET /status and GET /agent?format=json; it is usually this service's port

• 1. /human/ links to it.

Files, shell commands and model calls all run in this service's container: nothing leaves the GPU machine.

• The app port has no per-session isolation: it sees every session and file, and its project is the folder home (/scratch/home).
• It has no params filtering: the TUI runs the agent's tools, shell included, which is what the agent can already do inside its container.

Quick start

SID=$(curl -s -X POST {{BASE_URL}}/v1/sessions {{AUTH}} \
  -H "Content-Type: application/json" -d '{"title": "demo"}' | jq -r .id)

curl -s -X POST {{BASE_URL}}/v1/sessions/$SID/messages {{AUTH}} \
  -H "Content-Type: application/json" \
  -d '{"text": "write hello.py that prints hi and run it"}' | jq '{text, steps, elapsed_s, tools: [.tools[] | {tool, status}]}'

curl -s {{BASE_URL}}/v1/sessions/$SID/files {{AUTH}}
curl -s "{{BASE_URL}}/v1/sessions/$SID/files?path=hello.py" {{AUTH}}

Routes

POST /v1/sessions

Creates a session with a fresh empty directory. The body is optional: {"title": "..."}. Returns 201 with {"id": "ses_...", "title": ..., "created": <unix time>}.

POST /v1/sessions/{id}/messages

Sends one task or follow-up to the session. The agent remembers earlier messages in the same session.

• text (string, required): what to do.
• wait (bool, default true): with true, the request blocks until the agent's turn is over. That can take a few seconds or several minutes, so set your client timeout to at least 10 minutes. With false, it returns 202 at once; follow the turn on the events stream.

Reply (with wait: true):

{"id": "msg_...", "role": "assistant", "text": "Created hello.py ... prints: hi",
 "tools": [{"tool": "write", "status": "completed", "input": {...}, "output": "..."},
           {"tool": "bash", "status": "completed", "input": {"command": "python3 hello.py"}, "output": "hi\n"}],
 "steps": 3, "tokens": {...}, "finish": "stop", "elapsed_s": 6.2}

tools lists every tool call in the turn, and each output is cut to 4000 characters. When the model call itself fails (for example, the prompt is longer than the context), the reply carries an error object.

GET /v1/sessions/{id}/events

Server-sent events for this session: opencode's own event objects (message parts as they stream, tool calls, session.idle when a turn ends), one data: line each. The stream stays open; close it when you are done.

curl -sN {{BASE_URL}}/v1/sessions/$SID/events {{AUTH}}

GET /v1/sessions/{id}/files[?path=...]

With no path, or a directory path, it lists entries: {"path": ".", "entries": [{"name": "hello.py", "type": "file", "size": 12}]}. type is file, dir or other (a FIFO, socket or device).

A file path returns the file's bytes as a download (Content-Disposition: attachment). The agent wrote these bytes, so they are never served as a web page: the type is text/plain, image/png, image/jpeg, image/gif or image/webp when the extension says so, and application/octet-stream for everything else (.py, .html, .svg...). A path that leaves the session directory, contains a NUL byte, or names something other than a regular file or directory returns 400. A missing path returns 404.

PUT /v1/sessions/{id}/files?path=...

Uploads the raw request body to path in the session directory, creating parent directories as needed. 400 if path exists and is not a regular file. Returns 201 with {"written": "data/input.csv", "bytes": 1234}.

curl -s -X PUT "{{BASE_URL}}/v1/sessions/$SID/files?path=data/input.csv" {{AUTH}} \
  --data-binary @input.csv

POST /v1/sessions/{id}/abort

Stops the session's running turn. A messages request waiting on that turn then returns early.

GET /v1/agent

What this agent is: harness, model and sandbox policy.

GET /status

Start-up progress: phase is building, starting, loading, ready or error. network summarises the sandbox's outbound connections, and lists blocked attempts.

Timings and concurrency

• First start builds the container image, which takes a few minutes. After that, the service is ready once Basalt has loaded the 87 GB pack: about a minute when it is in the page cache, a few minutes cold (budgeted at 300 s).
• A small task such as the quick start takes about 3–10 s, and bigger tasks take minutes. Generation runs at about 300 tok/s; time depends on how many steps the agent takes.
• Sessions are independent, but the model answers one request at a time: parallel sessions take turns. Send one message at a time per session, and wait for the turn to end before you send the next.
• Sessions and their files live only as long as this run of the service. Download what you want to keep.

Errors

• 401: missing or wrong token. Send Authorization: Bearer <token>.
• 503 with Retry-After while the service is still starting: wait and retry.
• 404: unknown session id, file not found, or a route this service does not offer.
• 400: the body is not a JSON object, text is missing, or a path escapes the session.
• 5xx otherwise: retry once, then check GET /status.