API Server

The API server exposes nastech-agent as an OpenAI-compatible HTTP endpoint. Any frontend that speaks the OpenAI format — Open WebUI, LobeChat, LibreChat, NextChat, ChatBox, and hundreds more — can connect to nastech-agent and use it as a backend.

Your agent handles requests with its full toolset (terminal, file operations, web search, memory, skills) and returns the final response. When streaming, tool progress indicators appear inline so frontends can show what the agent is doing.

One backend covers models + tools

Nastech itself needs a configured provider and tool backends for the API server to be useful. A Nastech Portal subscription handles both — 300+ models plus web/image/TTS/browser via the Tool Gateway. Run nastech setup --portal once before starting the API server and frontends like Open WebUI or LobeChat get a fully tool-equipped backend.

Quick Start

1. Enable the API server

Add to ~/.nastech/.env:

API_SERVER_ENABLED=true
API_SERVER_KEY=change-me-local-dev
# Optional: only if a browser must call Nastech directly
# API_SERVER_CORS_ORIGINS=http://localhost:3000

2. Start the gateway

nastech gateway

You'll see:

[API Server] API server listening on http://127.0.0.1:8642

3. Connect a frontend

Point any OpenAI-compatible client at http://localhost:8642/v1:

# Test with curl
curl http://localhost:8642/v1/chat/completions \
  -H "Authorization: Bearer change-me-local-dev" \
  -H "Content-Type: application/json" \
  -d '{"model": "nastech-agent", "messages": [{"role": "user", "content": "Hello!"}]}'

Or connect Open WebUI, LobeChat, or any other frontend — see the Open WebUI integration guide for step-by-step instructions.

Endpoints

POST /v1/chat/completions

Standard OpenAI Chat Completions format. Stateless — the full conversation is included in each request via the messages array.

Request:

{
  "model": "nastech-agent",
  "messages": [
    {"role": "system", "content": "You are a Python expert."},
    {"role": "user", "content": "Write a fibonacci function"}
  ],
  "stream": false
}

Response:

{
  "id": "chatcmpl-abc123",
  "object": "chat.completion",
  "created": 1710000000,
  "model": "nastech-agent",
  "choices": [{
    "index": 0,
    "message": {"role": "assistant", "content": "Here's a fibonacci function..."},
    "finish_reason": "stop"
  }],
  "usage": {"prompt_tokens": 50, "completion_tokens": 200, "total_tokens": 250}
}

Inline image input: user messages may send content as an array of text and image_url parts. Both remote http(s) URLs and data:image/... URLs are supported:

{
  "model": "nastech-agent",
  "messages": [
    {
      "role": "user",
      "content": [
        {"type": "text", "text": "What is in this image?"},
        {"type": "image_url", "image_url": {"url": "https://example.com/cat.png", "detail": "high"}}
      ]
    }
  ]
}

Uploaded files (file / input_file / file_id) and non-image data: URLs return 400 unsupported_content_type.

Streaming ("stream": true): Returns Server-Sent Events (SSE) with token-by-token response chunks. For Chat Completions, the stream uses standard chat.completion.chunk events plus Nastech' custom nastech.tool.progress event for tool-start UX. For Responses, the stream uses OpenAI Responses event types such as response.created, response.output_text.delta, response.output_item.added, response.output_item.done, and response.completed.

All SSE streams (Chat Completions, Responses, /api/sessions/{id}/chat/stream, /v1/runs/{id}/events) emit a : keepalive comment line whenever no event has been sent for 10 seconds, so long tool calls do not trip client idle timeouts. Standard SSE clients ignore comment lines; custom parsers must skip lines that start with :.

Tool progress in streams:

• Chat Completions: Nastech emits event: nastech.tool.progress for tool-start visibility without polluting persisted assistant text.
• Responses: Nastech emits spec-native function_call and function_call_output output items during the SSE stream, so clients can render structured tool UI in real time.

POST /v1/responses

OpenAI Responses API format. Supports server-side conversation state via previous_response_id — the server stores full conversation history (including tool calls and results) so multi-turn context is preserved without the client managing it.

Request:

{
  "model": "nastech-agent",
  "input": "What files are in my project?",
  "instructions": "You are a helpful coding assistant.",
  "store": true
}

Response:

{
  "id": "resp_abc123",
  "object": "response",
  "status": "completed",
  "model": "nastech-agent",
  "output": [
    {"type": "function_call", "status": "completed", "name": "terminal", "arguments": "{\"command\": \"ls\"}", "call_id": "call_1"},
    {"type": "function_call_output", "status": "completed", "call_id": "call_1", "output": "README.md src/ tests/"},
    {"type": "message", "role": "assistant", "content": [{"type": "output_text", "text": "Your project has..."}]}
  ],
  "usage": {"input_tokens": 50, "output_tokens": 200, "total_tokens": 250}
}

Tool calls in the output array were already executed server-side by the Nastech agent — they are replayed with "status": "completed" for structured tool UI, never as pending calls for the client to execute.

Inline image input: input[].content can contain input_text and input_image parts. Both remote URLs and data:image/... URLs are supported:

{
  "model": "nastech-agent",
  "input": [
    {
      "role": "user",
      "content": [
        {"type": "input_text", "text": "Describe this screenshot."},
        {"type": "input_image", "image_url": "data:image/png;base64,iVBORw0K..."}
      ]
    }
  ]
}

Uploaded files (input_file / file_id) and non-image data: URLs return 400 unsupported_content_type.

Multi-turn with previous_response_id

Chain responses to maintain full context (including tool calls) across turns:

{
  "input": "Now show me the README",
  "previous_response_id": "resp_abc123"
}

The server reconstructs the full conversation from the stored response chain — all previous tool calls and results are preserved. Chained requests also share the same session, so multi-turn conversations appear as a single entry in the dashboard and session history.

Named conversations

Use the conversation parameter instead of tracking response IDs:

{"input": "Hello", "conversation": "my-project"}
{"input": "What's in src/?", "conversation": "my-project"}
{"input": "Run the tests", "conversation": "my-project"}

The server automatically chains to the latest response in that conversation. Like the /title command for gateway sessions.

GET /v1/responses/{id}

Retrieve a previously stored response by ID.

DELETE /v1/responses/{id}

Delete a stored response.

GET /v1/models

Lists the agent as an available model. The advertised model name defaults to the profile name (or nastech-agent for the default profile). Required by most frontends for model discovery.

/v1/models is intentionally the cheap OpenAI-compat surface. It does not enumerate every authenticated provider/model combination Nastech can route to, and it does not do pricing or capability enrichment.

GET /api/model/options

Nastech-aware clients can request the same curated provider/model inventory used by the dashboard and TUI. This route uses the API server's normal bearer authentication and returns provider rows, model capability hints, and pricing metadata that do not belong in the OpenAI-compatible /v1/models response:

curl \
  -H "Authorization: Bearer $API_SERVER_KEY" \
  "http://127.0.0.1:8642/api/model/options"

That payload is the same substrate the dashboard Models page and the TUI model.options RPC use. It returns authenticated providers, curated model lists, per-model pricing, and model capability hints.

Normal opens are intentionally conservative for custom providers: Nastech probes only the currently selected custom endpoint so a stale or offline saved endpoint does not block the picker. An explicit refresh flips to full probing and busts the provider model cache:

curl \
  -H "Authorization: Bearer $API_SERVER_KEY" \
  "http://127.0.0.1:8642/api/model/options?refresh=1"

Use /v1/models when an OpenAI-compatible client only needs a model name to send back in chat/responses requests. Use /api/model/options when an authenticated UI needs the richer Nastech-specific picker metadata.

GET /v1/capabilities

Returns a machine-readable description of the API server's stable surface for external UIs, orchestrators, and plugin bridges.

{
  "object": "nastech.api_server.capabilities",
  "platform": "nastech-agent",
  "model": "nastech-agent",
  "auth": {"type": "bearer", "required": true},
  "features": {
    "chat_completions": true,
    "responses_api": true,
    "run_submission": true,
    "run_status": true,
    "run_events_sse": true,
    "run_stop": true
  }
}

Use this endpoint when integrating dashboards, browser UIs, or control planes so they can discover whether the running Nastech version supports runs, streaming, cancellation, and session continuity without depending on private Python internals.

Browser-extension control

Nastech can route browser tools through an authenticated extension that controls the browser session associated with the current Nastech session. The feature is disabled by default; set browser.extension_control.enabled to true to opt in:

browser:
  extension_control:
    enabled: true

The local API path also requires the API server bearer key. A controller may register only for an existing server session. Nastech derives the controller principal from authenticated server state; a client-supplied principal_id is ignored.

Discover the live contract through GET /v1/capabilities. The browser_extension_control object reports whether the feature is enabled, the protocol version, transport names, and the exact capability allowlist:

controller.noop
browser_back
browser_click
browser_navigate
browser_press
browser_screenshot
browser_scroll
browser_snapshot
browser_tab_activate
browser_tabs
browser_type

Requested capabilities outside that list are filtered out. Raw CDP, arbitrary script evaluation, console access, uploads, image extraction, and vision are not part of the controller protocol.

When a request has no bound controller identity, or when the feature is disabled, Nastech preserves the existing browser backend. Once the gateway binds a controller principal and transport family to the request, that extension lane is authoritative: missing, ambiguous, disconnected, or incapable controllers fail closed instead of silently switching to a different local/cloud browser. After an exact controller is selected, its result or error is authoritative and Nastech never retries the same action through another backend.

Local API registration

1. Send an authenticated POST /v1/browser-control/register with protocol_version, session_id, controller_id, browser_profile_id, and the requested capabilities.
2. Nastech returns a single-use ticket with a 30-second TTL and the filtered, server-bound controller scope.
3. Open GET /v1/browser-control/ws with both WebSocket subprotocols: nastech-browser-control-v1 and nastech-browser-control-ticket.<ticket>.

The ticket is never accepted in the query string. Unknown, expired, reused, or malformed tickets fail before WebSocket upgrade.

Controller frames

Nastech sends browser.controller.command frames containing command_id, action, immutable arguments, browser/controller ids, and the originating tool_call_id. The controller replies with browser.controller.result, the same command_id, an exact boolean ok, and either result or error. Cancellation and timeout emit browser.controller.cancel; late results are ignored.

An unexpected socket loss marks the controller offline and preserves work already in flight until each command's original deadline. A reconnect with the same principal, profile, session, controller id, browser profile, and transport identity refreshes the transport without admitting new work before any deferred cancels are flushed. Negotiated capabilities may change on that reconnect; they are not an identity field. A different controller id or browser profile in the same authenticated session lane is a hard replacement: old pending work is cancelled before the successor becomes routable. Send browser.controller.detach on the authenticated controller transport for an intentional hard detach — that immediately cancels pending work. Merely closing the socket is treated as a recoverable disconnect.

The authenticated dashboard transport exposes the same registration, result, heartbeat, capability, and ownership semantics over its Gateway RPC/event channel. In both transports, selection requires one unambiguous exact match on principal, profile, session, controller, browser profile, transport family, and capability. Once selected, a controller failure is authoritative and is never retried through a different browser backend.

Per-request model selection

Authenticated clients can override Nastech' default model selection per request by sending:

• model — the target model id for this turn
• provider — the Nastech provider slug to resolve credentials/runtime for this turn
• model_options — request-scoped reasoning / service-tier controls

The same request fields are accepted on:

• POST /v1/chat/completions
• POST /v1/responses
• POST /v1/runs
• POST /api/sessions/{session_id}/chat
• POST /api/sessions/{session_id}/chat/stream

Precedence is deterministic:

1. Session /model override, if that session already has one
2. A static gateway.platforms.api_server.model_routes mapping selected when the request's model is a configured route alias
3. Direct request model / provider when no route alias matches
4. Global gateway config / environment defaults

model_options stays request-scoped regardless of which model/provider wins. If a request sends a provider that conflicts with a configured model_routes alias, Nastech rejects the request with 400 instead of silently remixing route credentials with another provider.

Bare model values on the OpenAI-compatible endpoints are opt-in. Generic OpenAI clients routinely hardcode model names (gpt-4o, ...), and existing deployments rely on those falling back to the gateway default. On POST /v1/chat/completions and POST /v1/responses, a model value sent WITHOUT a provider is therefore ignored unless you enable:

gateway:
  platforms:
    api_server:
      direct_model_requests: true

Requests that include an explicit provider — and the Nastech-native /v1/runs and session-chat endpoints — always honor the requested model regardless of this flag.

Example:

{
  "model": "MiniMax-M3",
  "provider": "minimax",
  "model_options": {
    "reasoning_effort": "high",
    "service_tier": "priority"
  },
  "messages": [
    {"role": "user", "content": "Summarize the repo status."}
  ]
}

GET /health

Health check. Returns {"status": "ok"}. Also available at GET /v1/health for OpenAI-compatible clients that expect the /v1/ prefix.

GET /health/detailed

Authenticated readiness check for monitoring and control planes. It reports bounded status for the active profile's config, state database, configured model, disk space, gateway/platform state, active API runs, pending process completions, and active delegations. The response exposes status and counts, not config values, credentials, paths, commands, queue payloads, or raw errors.

The public /health route remains a cheap liveness probe and does not run readiness checks. A degraded readiness result still uses HTTP 200; inspect the top-level status and readiness.checks fields.

Runs API (streaming-friendly alternative)

In addition to /v1/chat/completions and /v1/responses, the server exposes a runs API for long-form sessions where the client wants to subscribe to progress events instead of managing streaming themselves.

POST /v1/runs

Create a new agent run. Returns a run_id that can be used to subscribe to progress events.

{
  "run_id": "run_abc123",
  "status": "started"
}

Runs accept a simple input string and optional session_id, instructions, conversation_history, or previous_response_id. When session_id is provided, Nastech surfaces it in the run status so external UIs can correlate runs with their own conversation IDs.

For safely retryable creation, send an Idempotency-Key header (1–255 visible ASCII characters). Nastech durably reserves the key before starting work. An identical retry returns the original run_id with HTTP 202 and Idempotency-Replayed: true, including after a gateway restart and after the run has completed, failed, or been cancelled. Reusing the same key with a different JSON payload returns HTTP 409 with code idempotency_key_conflict. Keys are isolated by authenticated API profile/credential and retained for 24 hours after their last status update; clients should use unique, unguessable keys and must not reuse them for unrelated operations. Requests without the header retain the legacy behavior and always create a new run.

When session_id identifies an existing Nastech session and no explicit conversation_history or previous_response_id is supplied, the run loads that session's active transcript. Session turn leases serialize concurrent writers and refresh the transcript after a contended wait.

GET /v1/runs/{run_id}

Poll the current run state. This is useful for dashboards that need status without holding an SSE connection open, or for UIs that reconnect after navigation.

{
  "object": "nastech.run",
  "run_id": "run_abc123",
  "status": "completed",
  "session_id": "space-session",
  "model": "nastech-agent",
  "output": "Done.",
  "usage": {"input_tokens": 50, "output_tokens": 200, "total_tokens": 250}
}

Statuses are retained briefly after terminal states (completed, failed, cancelled, or interrupted) for polling and UI reconciliation. When the gateway shuts down while a run is active, the run is persisted as interrupted (error Gateway shutdown interrupted the run., terminal event run.interrupted) before the agent is asked to stop, so a durable run never survives a restart as running; a late result from the interrupted turn cannot overwrite it.

GET /v1/runs/{run_id}/events

Server-Sent Events stream of the run's tool-call progress, token deltas, and lifecycle events. Designed for dashboards and thick clients that want to attach/detach without losing state.

Tool lifecycle events carry tool.started (tool, preview of the arguments) and tool.completed (tool, duration in seconds, error, and a preview of the result). The error flag reflects the tool's own outcome — a non-zero terminal exit_code, a structured {"error": ...} result, a denied approval — whether the result arrives as a JSON string or an already-parsed object. The completion preview is the result text (structured results are JSON-encoded), passed through forced secret redaction and then truncated to 500 characters, so a client can tell an approval refusal (BLOCKED: ...) from an ordinary failure without receiving the unbounded tool payload.

When the agent delegates work to background subagents, the stream also carries subagent.start and subagent.complete lifecycle events, so clients can observe delegation outcomes — including timeouts and failures — instead of the run going silent while a child works. The subagent.complete payload carries the child's status, summary, duration, token/cost figures, a child_session_id for correlation, and the delegation_id of the batch it belongs to (so concurrent or nested fan-outs stay distinguishable); free-text fields pass forced secret redaction before leaving the process. Per-tool child events (subagent.tool, progress ticks) are intentionally not forwarded — they are high-volume UI noise; use the per-child live transcript files for play-by-play. These events are available while the parent stream is open; a late detached completion does not reopen a finished run's SSE stream or change its terminal status.

Detached results and session history

Background delegation requires a continuation that reads server-side session history: an explicit X-Nastech-Session-Id on Chat Completions, a native /api/sessions/{id}/chat request, or a Runs request using session history. Header-less Chat Completions, Responses chains, and Runs requests with previous_response_id or caller-supplied history instead execute delegation synchronously, returning the result in the original turn. Merely deriving a session ID from request content does not enable detached delivery.

For resumable requests, the completion is persisted once per delegation unit. It is available through GET /api/sessions/{id}/messages and in the next real client turn's session history. Retries do not insert the same result again; interim task-failure notices have separate identities. Delivery waits while a client turn owns the session lease and follows compression continuations. Chat Completions echoes the explicit session ID you supplied in both JSON and streaming responses; keep sending that ID even after compression.

A completion never starts an unsolicited model turn or bypasses a pending human confirmation. The client owns the next turn. Clients that continue using their own history snapshots should use synchronous delegation rather than expecting a server-side delivery row to be merged into those snapshots.

Unconsumed event buffers expire after five minutes so a detached client cannot grow memory indefinitely. This expires transport state only: a run that is still executing remains visible to status polling, approval, stop control, and concurrency accounting until its executor work actually exits. A connected SSE subscriber continues draining normally.

POST /v1/runs/{run_id}/stop

Interrupt a running agent turn. The endpoint returns immediately with {"status": "stopping"} while Nastech asks the active agent to stop at the next safe interruption point. The run stays tracked as stopping until the executor-backed work exits, then settles as cancelled; requesting stop never hides a worker that is still running.

POST /v1/runs/{run_id}/approval

Resolve a pending approval for a run that is waiting on a human decision (for example, a tool call gated behind an approval policy). The body carries the approval decision; the run resumes once the decision is recorded. This endpoint is advertised in /v1/capabilities as the run_approval feature so external UIs can detect support before surfacing an approval prompt.

MCP trust-gate consent — a write-capable tool on a server configured trust: untrusted — surfaces the same way: the run emits an approval.request event and parks in waiting_for_approval until this endpoint resolves it (once runs the tool, deny blocks it).

Jobs API (background scheduled work)

The server exposes a lightweight jobs CRUD surface for managing scheduled / background agent runs from a remote client. All endpoints are gated behind the same bearer auth.

GET /api/jobs

List all scheduled jobs.

POST /api/jobs

Create a new scheduled job. Body accepts the same shape as nastech cron — prompt, schedule, skills, provider override, delivery target.

GET /api/jobs/{job_id}

Fetch a single job's definition and last-run state.

PATCH /api/jobs/{job_id}

Update fields on an existing job (prompt, schedule, etc.). Partial updates are merged.

DELETE /api/jobs/{job_id}

Remove a job. Also cancels any in-flight run.

POST /api/jobs/{job_id}/pause

Pause a job without deleting it. Next-scheduled-run timestamps are suspended until resumed.

POST /api/jobs/{job_id}/resume

Resume a previously paused job.

POST /api/jobs/{job_id}/run

Trigger the job to run immediately, out of schedule.

Sessions API (session control over REST)

External UIs can manage Nastech sessions over REST without standing up the dashboard. All endpoints are gated by API_SERVER_KEY and live under /api/sessions/*.

Method	Path	Description
GET	/api/sessions	List sessions (paginated — limit, offset, source, include_children)
POST	/api/sessions	Create an empty session
GET	/api/sessions/{id}	Read session metadata
PATCH	/api/sessions/{id}	Update title or end_reason
DELETE	/api/sessions/{id}	Delete a session
GET	/api/sessions/{id}/messages	Message history for a session
POST	/api/sessions/{id}/fork	Branch the session via SessionDB lineage (matches CLI /branch semantics)
POST	/api/sessions/{id}/chat	Run one synchronous agent turn
POST	/api/sessions/{id}/chat/stream	SSE wrapper over a single turn — emits assistant.delta, tool.started, tool.completed, then a terminal run.completed / run.failed / run.cancelled event that matches how the turn ended (see Terminal run status)

/v1/capabilities advertises the full surface via session_* feature flags and endpoints.session_* entries so external UIs can detect support and fall back safely. Inline images are supported in chat and chat/stream payloads (multimodal-aware path).

# fork a session and run one turn
curl -X POST http://localhost:8642/api/sessions/$ID/fork \
  -H "Authorization: Bearer $API_SERVER_KEY" \
  -d '{"title": "explore alt path"}'

# stream a turn over SSE
curl -N -X POST http://localhost:8642/api/sessions/$ID/chat/stream \
  -H "Authorization: Bearer $API_SERVER_KEY" \
  -d '{"input": "what files changed in the last hour?"}'

Skills and toolsets discovery

GET /v1/skills and GET /v1/toolsets let external clients enumerate the agent's capabilities deterministically over REST instead of asking the model. Both are read-only and gated by API_SERVER_KEY.

curl http://localhost:8642/v1/skills \
  -H "Authorization: Bearer $API_SERVER_KEY"
# → [{"name": "github-pr-workflow", "description": "...", "category": "..."}, ...]

curl http://localhost:8642/v1/toolsets \
  -H "Authorization: Bearer $API_SERVER_KEY"
# → [{"name": "core", "label": "...", "description": "...", "enabled": true,
#     "configured": true, "tools": ["read_file", "write_file", ...]}, ...]

/v1/skills returns the same metadata the skills hub uses internally. /v1/toolsets returns toolsets resolved for the api_server platform with the concrete tools list each one expands to. Both are advertised under endpoints.* in /v1/capabilities.

Long-term memory scoping (X-Nastech-Session-Key)

Multi-user frontends like Open WebUI need a stable per-channel identifier for long-term memory (Honcho, etc.) that is independent of the transcript-scoped X-Nastech-Session-Id (which rotates on /new). Pass X-Nastech-Session-Key on /v1/chat/completions, /v1/responses, or /v1/runs and Nastech threads it through to AIAgent(gateway_session_key=...), where the Honcho memory provider uses it to derive a stable scope.

POST /v1/chat/completions HTTP/1.1
Authorization: Bearer ***
X-Nastech-Session-Id: transcript-alpha
X-Nastech-Session-Key: agent:main:webui:dm:user-42

Rules: max 256 chars, control characters (\r, \n, \x00) are rejected, and the value is echoed back on responses (JSON + SSE). /v1/capabilities advertises support via "session_key_header": "X-Nastech-Session-Key". Without the key, Honcho's per-session strategy produces a different scope per session_id — exactly the behavior Nastech had before.

System Prompt Handling

When a frontend sends a system message (Chat Completions) or instructions field (Responses API), nastech-agent layers it on top of its core system prompt. Your agent keeps all its tools, memory, and skills — the frontend's system prompt adds extra instructions.

This means you can customize behavior per-frontend without losing capabilities:

• Open WebUI system prompt: "You are a Python expert. Always include type hints."
• The agent still has terminal, file tools, web search, memory, etc.

Authentication

Bearer token auth via the Authorization header:

Authorization: Bearer ***

Configure the key via API_SERVER_KEY env var. If you need a browser to call Nastech directly, also set API_SERVER_CORS_ORIGINS to an explicit allowlist.

Multi-profile routing (/p/<profile>/…)

When multi-profile gateway routing is enabled (gateway.multiplex_profiles), the shared listener serves every profile through a /p/<profile>/ URL prefix — and authentication is bound to the routed profile:

• Requests to /p/<profile>/v1/... must present that profile's own API_SERVER_KEY (from ~/.nastech/profiles/<profile>/.env). The default listener's key is rejected on named-profile prefixes.
• Unprefixed routes and /p/default/... keep using the default profile's key.
• A named profile with no API_SERVER_KEY of its own fails closed — its prefix is unreachable until you set one.
• Runs are per-profile scoped: /v1/runs/{run_id} and its events, stop, steer, and approval routes only answer for the profile that created the run (including runs started via /api/sessions/{id}/chat/stream); another profile's run id returns 404, never 403.

Breaking change (July 2026)

Before this fix, a valid default-profile key was accepted on any /p/<profile>/ prefix. If you relied on one shared key across profile prefixes, set a distinct API_SERVER_KEY in each profile's .env — reused default keys on named prefixes now return 401.

Security

The API server gives full access to nastech-agent's toolset, including terminal commands. API_SERVER_KEY is required for every deployment, including the default loopback bind on 127.0.0.1. Keep API_SERVER_CORS_ORIGINS narrow to control browser access when you explicitly allow browser callers.

Configuration

Environment Variables

Variable	Default	Description
API_SERVER_ENABLED	false	Enable the API server
API_SERVER_PORT	8642	HTTP server port
API_SERVER_HOST	127.0.0.1	Bind address (localhost only by default)
API_SERVER_KEY	(required)	Bearer token for auth
API_SERVER_CORS_ORIGINS	(none)	Comma-separated allowed browser origins
API_SERVER_MODEL_NAME	(profile name)	Model name on /v1/models. Defaults to profile name, or nastech-agent for default profile.

config.yaml

The same settings can live in ~/.nastech/config.yaml under a nested gateway.api_server: section:

gateway:
  api_server:
    enabled: true
    port: 8642
    host: 127.0.0.1
    key: your-secret-key
    cors_origins: http://localhost:3000
    model_name: my-nastech
    max_concurrent_runs: 10   # concurrent-run cap; 0 disables the limit

port, key, host, cors_origins, and model_name are automatically bridged into the platform's extra settings, so they behave exactly like their API_SERVER_* environment-variable counterparts. Environment variables take precedence over config.yaml values. The block is also accepted under gateway.platforms.api_server: or a top-level platforms.api_server: section.

Concurrent-run cap

The API server limits how many agent runs may execute at once across the endpoints that start one directly: the OpenAI-compatible endpoints, the Runs endpoints, and the session-chat endpoints (POST /api/sessions/{id}/chat and its /stream variant, which carry cross-machine agent DMs). Cron-triggered runs (POST /api/jobs/{id}/run, POST /api/cron/fire) go through the cron scheduler and are governed by cron's own limits, not this cap. The cap is read from gateway.api_server.max_concurrent_runs (default 10; 0 disables the limit, negative values clamp to 0). When the cap is reached, new run-starting requests are rejected with HTTP 429 Too many concurrent runs (max N) — clients should back off and retry.

Security Headers

All responses include security headers:

• X-Content-Type-Options: nosniff — prevents MIME type sniffing
• Referrer-Policy: no-referrer — prevents referrer leakage

CORS

The API server does not enable browser CORS by default.

For direct browser access, set an explicit allowlist:

API_SERVER_CORS_ORIGINS=http://localhost:3000,http://127.0.0.1:3000

When CORS is enabled:

• Preflight responses include Access-Control-Max-Age: 600 (10 minute cache)
• SSE streaming responses include CORS headers so browser EventSource clients work correctly
• X-Nastech-Session-Id is an allowed request header, so browsers on an allowlisted origin can request session continuation.
• Idempotency-Key is an allowed request header — clients can send it for deduplication (responses are cached by key for 5 minutes)

Most documented frontends such as Open WebUI connect server-to-server and do not need CORS at all.

Compatible Frontends

Any frontend that supports the OpenAI API format works. Tested/documented integrations:

Frontend	Stars	Connection
Open WebUI	126k	Full guide available
LobeChat	73k	Custom provider endpoint
LibreChat	34k	Custom endpoint in librechat.yaml
AnythingLLM	56k	Generic OpenAI provider
NextChat	87k	BASE_URL env var
ChatBox	39k	API Host setting
Jan	26k	Remote model config
HF Chat-UI	8k	OPENAI_BASE_URL
big-AGI	7k	Custom endpoint
OpenAI Python SDK	—	OpenAI(base_url="http://localhost:8642/v1")
curl	—	Direct HTTP requests

Multi-User Setup with Profiles

To give multiple users their own isolated Nastech instance (separate config, memory, skills), use profiles:

# Create a profile per user
nastech profile create alice
nastech profile create bob

# Configure each profile's API server on a different port. API_SERVER_* are env
# vars (not config.yaml keys), so write them to each profile's .env:
cat >> ~/.nastech/profiles/alice/.env <<EOF
API_SERVER_ENABLED=true
API_SERVER_PORT=8643
API_SERVER_KEY=alice-secret
EOF

cat >> ~/.nastech/profiles/bob/.env <<EOF
API_SERVER_ENABLED=true
API_SERVER_PORT=8644
API_SERVER_KEY=bob-secret
EOF

# Start each profile's gateway
nastech -p alice gateway &
nastech -p bob gateway &

Each profile's API server automatically advertises the profile name as the model ID:

• http://localhost:8643/v1/models → model alice
• http://localhost:8644/v1/models → model bob

In Open WebUI, add each as a separate connection. The model dropdown shows alice and bob as distinct models, each backed by a fully isolated Nastech instance. See the Open WebUI guide for details.

Limitations

• Response storage — stored responses (for previous_response_id) are persisted in SQLite and survive gateway restarts. Max 100 stored responses (LRU eviction).
• No file upload — inline images are supported on both /v1/chat/completions and /v1/responses, but uploaded files (file, input_file, file_id) and non-image document inputs are not supported through the API.
• Simple OpenAI clients still see an alias — /v1/models advertises the stable Nastech alias (nastech-agent or the active profile name). Richer clients can send explicit provider / model_options overrides on requests.

Proxy Mode

The API server also serves as the backend for gateway proxy mode. When another Nastech gateway instance is configured with GATEWAY_PROXY_URL pointing at this API server, it forwards all messages here instead of running its own agent. This enables split deployments — for example, a Docker container handling Matrix E2EE that relays to a host-side agent.

See Matrix Proxy Mode for the full setup guide.