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Codeman/docs/wiki/Custom-Model-Endpoints.md
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DevvynandClaude Sonnet 5 b45a96358e feat(custom-model): warn before launching Claude on a model too small for its own overhead
Claude Code's own fixed per-turn overhead (system prompt + tool schemas,
~36.4K tokens measured live) can exceed a small local model's entire real
context before any conversation history exists to compact — confirmed
live twice as an in:0 out:0 failure on the very first message sent.
CLAUDE_CODE_MAX_CONTEXT_TOKENS cannot fix this: it only governs when
history gets compacted, and there is none on message one.

- exceedsSafeContextFloor() (custom-model-routes.ts): true when a CLI's
  registry entry declares contextLengthVar (currently only claude) and
  the model's discovered context is below CLAUDE_MIN_SAFE_CONTEXT_TOKENS
  (40000). A no-op for every other CLI by construction.
- Both apply routes (POST /api/sessions/:id/custom-model and the
  quick-start customModel path) check this before the swap-conflict
  check and before launching/restarting anything, returning
  {requiresContextWarning, modelId, contextLength, minSafeContextTokens}
  — skipped when confirmed:true.
- Frontend: #customModelContextWarningModal + _confirmContextWarning/
  _resolveContextWarningConfirm (session-ui.js), wired into both
  _quickStartWithCustomModelConfirm and _runCustomModelEntryViaRestart
  (the path Claude actually uses) ahead of the swap-confirmation check.
  Explains the fix in-modal: give the model an explicit larger -c/
  --ctx-size in llama-swap instead of relying on --fit-ctx, which
  optimizes for the biggest model that fits rather than the biggest
  context.

Tests added for the route-level warning/confirm/skip cases and the
frontend modal + launch-flow wiring. Docs updated (custom-model-
endpoints.md, wiki/Custom-Model-Endpoints.md) and the PR's running
changeset extended.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RqZeHrRS6DYcGcGX2p9EwG
2026-09-17 07:36:57 +08:00

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# Custom Model Endpoints
Point a harness at your own OpenAI-compatible server instead of its native cloud backend, for
one session at a time. "Custom endpoint" covers **local** hardware (llama.cpp, Ollama, vLLM,
a home GPU rig, DGX Spark, Strix Halo) and **cloud** services (Azure AI Foundry's
OpenAI-compatible endpoint, OpenRouter, a company gateway) alike, anything answering
`GET /v1/models` and `POST /v1/chat/completions` in the standard shape.
**Off by default.** Turn it on in App Settings → Models → **Custom model endpoints**.
## Adding an endpoint
Still in App Settings → Models → Custom model endpoints:
1. **+ Add endpoint** — give it an id, a label, and the base URL (`http://192.168.1.50:8080`,
say). An API key is optional; most local servers don't check one.
2. **Discover** — fetches the endpoint's own model list over `GET /v1/models` and stores it.
3. Pick a **default model** from what was discovered. This is the model the Run-menu entry
applies directly when only one model is discovered; with two or more, it's just the one
pre-marked in the picker dialog described below, not a silent default.
Endpoint management is admin-only in multi-user mode, the same as remote hosts and Docker
hosts — these are machine-level infra, not a per-user setting.
**Model lists refresh themselves.** Every saved endpoint is re-discovered automatically every
5 minutes in the background, so a model the server starts serving later — or stops serving —
shows up without another manual click of **Discover**. One endpoint being unreachable on a
given cycle (powered off, wrong network) never blocks the others from refreshing.
**Context length is picked up automatically where it can be, safely.** Against a
llama.cpp/llama-swap server, discovery also learns each _currently loaded_ model's real
context window and applies it to the launched session (Claude Code today — see below), so
the harness stops assuming a large default window for a model name it doesn't recognise and
overflowing a much smaller real one. It's deliberately never probed for a model that isn't
already loaded, since asking a llama-swap server about an unloaded model can trigger an
actual, slow model swap as a side effect — a model just not currently loaded keeps whatever
context length an earlier cycle already learned for it instead.
## Running a session against one
With the setting on and at least one endpoint carrying a discovered model, the **Run**
dropdown grows a **Custom Endpoints** section: one entry per harness that can redirect to a
custom endpoint, per saved endpoint, e.g. "Claude Code (llama.cpp)". Picking one starts a
session on that harness exactly the way its own entry would. It is a one-off "try this
endpoint" action, not a sticky mode — the plain **Run** button still means "this harness,
native cloud" afterward, and a fresh session never inherits whatever the last one was
pointed at.
**Which model it uses depends on how many the endpoint has discovered.** With exactly one,
the session launches straight away on that model — nothing to choose. With two or more, a
small dialog asks which one to use for this launch before starting the session; the
endpoint's default model, if set, is marked but not auto-picked, so a launch can deliberately
use a different one without changing the saved default.
**For opencode, Codex, Gemini, Pi, Grok, DeepSeek and OMP, picking an entry launches
straight onto the endpoint** — no restart, because the endpoint is applied before the
session's process ever starts. **Claude still restarts the harness's process in place** —
same tab, same conversation (`--resume`) — after a normal native launch, since that restart
is far less jarring for Claude than for the other seven, whose own TUI can fully
reinitialize on a restart. Either way, every supported harness reads its endpoint config at
process start, never per turn, so there is no live hot-swap while a turn is running.
Picking an entry that launches a **brand-new** Claude session waits (up to 20 seconds) for it to
finish its own startup before applying — a freshly started CLI reports itself as busy for its
boot sequence, and applying to a genuinely busy session is refused so a real, in-progress
turn is never interrupted out from under you. A session that is still busy after that wait
(a very slow-starting CLI, or one you started typing into right away) surfaces that refusal
as an ordinary error, which now stays on screen with a close button instead of vanishing
after a few seconds — read it, it names the actual reason rather than a generic failure.
Entries are hidden entirely for a session in a **remote (SSH) or Docker case** — support for
redirecting those hasn't landed yet, see below. The picker also only appears in the desktop
**Run** dropdown; the phone home screen builds its own run picker separately and does not
currently offer these entries.
**Against llama-swap, applying a selection also starts the actual model load, rather than
waiting on your first prompt to do it.** llama-swap has no "switch model" button of its own
— the only thing that starts a swap is a real request naming the model, and confirmed live:
just applying a selection never reached llama-swap's own logs at all until something asked
it to load. Picking an entry now also sends the smallest real request that will trigger
that load, in the background, the moment the target model isn't already loaded and ready.
**The centred loading banner shows a live countdown, and a real timeout is an error, not a
shrug.** When it knows the model's discovered file size (its GB figure, when llama-swap
states one), it shows both a rough expected-time estimate and a live countdown against it —
e.g. "Loading qwen3.8-27b (16.4 GB, typically ~1–3 min) on llama-swap — 47s remaining". If
the countdown reaches zero and the model still isn't ready, the banner turns into a sticky
error telling you to check the llama-swap server's own logs, and **the session that load was
for is closed automatically** — a console left open and pointed at a model that never
finished loading would just be confusing to leave sitting there.
**Claude Code specifically gets two extra fixes applied automatically:**
- Its discovered context length (see above) is passed through as
`CLAUDE_CODE_MAX_CONTEXT_TOKENS`, so it doesn't send a full-size prompt against a much
smaller real local context and overflow it.
- Its session runs with an isolated `CLAUDE_CONFIG_DIR`, so the injected API key never sits
in the same directory as a stored claude.ai login — that combination is harmless for actual
requests (the API key wins) but the CLI still prints a "both claude.ai and
ANTHROPIC_API_KEY set" warning about it, which this avoids entirely. The isolated directory
keeps a link back to your real session history so the response viewer and similar features
still work for that session. That isolated directory starts with no prior approvals of its
own, so Codeman also pre-approves the injected key the same way answering Claude Code's own
"Detected a custom API key" prompt once would — without it, that prompt would otherwise
reappear on every single launch with nobody there to answer it.
**If a model's real context is too small for Claude Code to even get started, you get a
warning instead of a confusing failure.** Claude Code's own system prompt and tools take up
roughly 40K tokens on their own, before you've typed anything — a small local model with a
smaller real context than that fails outright on the very first message, no matter what
context size Codeman tells it to expect (raising the declared context only changes when
Claude Code trims _conversation history_, and there is none yet on message one). Picking
such a model now shows an in-app dialog naming the model, its discovered context and what's
needed, before anything launches or restarts, with the fix spelled out: reconfigure
llama-swap to give that model (or a smaller one) an explicit larger context instead of
relying on auto-fit (`--fit-ctx`), which sizes the context around fitting the biggest model
rather than the biggest context — for example adding `-c 65536` to that model's llama-swap
entry. "Launch anyway" is still there if you want to try regardless.
## Which harnesses actually work
| Harness | Status |
| ---------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------- |
| **Claude Code, opencode, Pi, Grok, OMP** | Verified end-to-end against a real local server. |
| **Codex** | Config is correct, but Codex only speaks the Responses API, which llama.cpp-style servers don't implement. A protocol gap, not a Codeman bug. |
| **Gemini** | Fails with an auth error gemini-cli raises once redirected. Unresolved; don't rely on it yet. |
| **DeepSeek** | Reaches the server but gets a consistent 404. Root cause not identified. |
| **Antigravity** | No known custom-endpoint mechanism at all. Not offered. |
Which harnesses show up in the Run-menu picker is read live off Codeman's own CLI registry,
not a fixed list here, so this table can go stale before this page does — a greyed-out or
missing entry is the more current answer.
## What it does not do
- **No remote or Docker sessions yet.** Both restart their agent differently under the hood
(reattaching a durable tmux session rather than relaunching the process), so redirecting
them needs its own plumbing that hasn't been built.
- **No live hot-swap mid-conversation.** Applying a selection always restarts the process.
- **No button to un-point a session from the UI yet.** Clearing back to native cloud is an
HTTP call (`POST .../custom-model {"clear": true}`) or deleting the session; the settings
panel manages saved endpoints, not what a running session is currently pointed at.
- **Nothing is shared with your real cloud credentials.** The endpoint's own key, if any,
never touches your Anthropic/OpenAI/Google login — a custom endpoint is a separate,
explicit choice per session.
## Security
An endpoint's base URL can't point at a link-local or cloud-metadata address (both at save
time and against the address it actually resolves to), the same guard Web Tabs uses for
saved dashboards. Endpoint records and any per-session config files a harness needs are
written with owner-only permissions. See
[custom-model-endpoints-plan.md](https://github.com/Ark0N/Codeman/blob/master/docs/custom-model-endpoints-plan.md)
in the repository for the full design reasoning, including why this feature closed a
pre-existing gap in how session environment overrides were guarded rather than opening a new
one.