billion-context

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📄 Paper / Preprint

• Model-Driven Incremental Hierarchical Compression: Training-Free Multi-Generational Context Management for Long-Lived Coding Agents (English, v0.2)

📝 The paper itself is open-sourced under the MIT License as part of the codebase (paper/). It is a living document — anyone may edit it; improvements are welcome via pull request.

A production-scale longitudinal study: 4.5 months, three hosts, 174,327 model calls, 18.76B cumulative input tokens (~24.7B across all hosts), zero window violations on 204,800-token models, marathon sessions of 8,584–12,049 calls.

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billion-context sits between any agent and its model API, rewriting Anthropic/OpenAI streams with acp-kernel compression. The model decides when and what to compress into high-fidelity summaries — not a hard truncation limit.

Community

Discussion, help, and updates on QQ — one group covers all three projects (billion-context, billion-context-pi, opencode-acp):

QQ Group: 1056132097

Why

Long coding sessions blow up context. Each provider charges per token, and once you pass the context window the session degrades or dies. billion-context compresses consumed conversation into layered summaries so you can run a single session for days — billions of tokens through one context window.

Unlike a host's built-in summarizer, compression here is incremental, reversible, and prefix-cache friendly: summaries are written in small ranges, can be decompressed on demand, and the cache prefix stays intact.

How it works

Agent (Claude Code / Codex / Cursor / Aider ...)
        │  you point the agent's base URL at the proxy
        ▼
┌─────────────────┐
│  billion-context│   1. parse the request (Anthropic or OpenAI shape)
│     proxy       │   2. run acp-kernel compression on the conversation
│                 │   3. inject a `compress` tool + compression philosophy
│                 │   4. forward to the real model API
│                 │   5. rewrite the streaming response
└─────────────────┘
        │
        ▼
   real model API (Anthropic / OpenAI / compatible)

The proxy injects four context-management tools (compress, decompress, search_context, acp_status) into the conversation. The model calls compress when the conversation grows, and the proxy executes it server-side — the compressed ranges are folded into the conversation history before the next turn.

An opt-in fifth tool, absorb (compress.absorb.enabled: true — see CONFIGURATION.md), compresses individual tool results the moment they arrive: large results (builds, logs, greps) get a forced absorb instruction, the model distills each into a compact summary, and the original pair is hidden from the wire from the next turn on — keeping mid-session pressure lower between fold rounds (#605).

Two compression modes — who executes compress

The proxy runs in one of two modes, and the mode decides who executes compress, which in turn decides how the summary travels to the model (the "carrier"). This distinction is the root of #377.

	Launcher / plugin mode (bili pi, bili codex, …)	Proxy mode (plain client → /bili/)
Client	ACP-native agent with the bili extension (pi/omp)	Any OpenAI/Anthropic client, no extension
Who executes compress	The agent (pi runs it locally)	The proxy (server-side compress loop)
compress tool call in the re-sent history?	Yes — part of the agent's own conversation	No — ephemeral proxy-loop traffic
Preflight blocks (no tool call)?	Last-resort backstop — the agent normally compresses on its own compress calls, but src/preflight.ts still fires (in both modes) when the input alone exceeds the window (#470)	Yes — src/preflight.ts compresses behind the client's back
Summary carrier on the wire	the compress tool call	an acp_summary user message
System messages on the wire	always exactly 1 (client + prompt)	always exactly 1 (client + prompt) — summaries ride on user messages
SGLang "single system" 400 (#377)	cannot happen	cannot happen (summaries are user messages, not system)
Proxy-injected compress tools	none — the agent registers the 4 ACP tools natively	the 4 context tools (when enabled)
Proxy-injected nudge	yes — the agent has no nudge channel of its own, so the proxy-side nudge is the proactive compression trigger (preflight alone only fires at the hard limit; #451)	yes (when enabled)

Why the carriers differ. In plugin mode the agent owns compression: the compress call + result live in the agent's own history and are re-sent every turn, so the summary rides on the tool call and the agent's view never renders the kernel's acp_summary fallback (billion-context-pi src/messages.ts skips acp_summary_*). In proxy mode the client is not ACP-native, so the proxy executes compress server-side; the tool call never enters the client's history, and preflight blocks have no tool call at all — so the kernel's acp_summary message is the only carrier. The kernel renders it as role system, but strict OpenAI-compatible backends (SGLang) require exactly one system message at index 0, so systemToUser (src/util.ts) re-voices it as a user message, leaving it at its anchor position. This keeps the head system message (the prefix-cache anchor) byte-stable across compress turns, so a new block does not invalidate the whole-conversation prefix.

Why user, not system or a forged tool call. A mid-stream system message is what SGLang rejects (#377). A forged compress tool call would be the "pure" carrier, but in proxy mode it requires fabricating an assistant tool_calls + user tool_result pair by id, declaring the tool in the request, and handling preflight blocks that have no authentic call — far more invasive than re-voicing a standalone note. A user message is allowed anywhere in the conversation, so it is the minimal change that satisfies both SGLang's one-system rule and prefix-cache stability. The accepted trade-off: a summary is a stand-in for the folded history, and re-voicing it as a user turn is a semantic mismatch the model tolerates (it is clearly marked [Compressed conversation section]).

Do the two modes coexist?

• Same proxy instance: yes, by design. One proxy serves plugin and plain clients at once; pluginMode is decided per request (x-bili-plugin header) and bound per session (session.metadata.pluginAgent). The launcher reuses a running proxy.
• Same session: the mode is sticky. A session created in plugin mode stays plugin mode (metadata inheritance); a plain session can only be upgraded to plugin mode if a plugin request arrives with a matching conversation id (the header outranks) — and never downgraded. In practice a plain→plugin upgrade requires the plugin client's conversation id to match an existing plain session id, which doesn't happen (each client generates its own id).
• Cross-mode block hazard: theoretical only. It would require the same conversation id to span a mode switch. plugin→proxy is safe (the tool call is in the shared history); proxy→plugin could orphan proxy-created block summaries (their tool call isn't in the agent's history and the agent's view skips acp_summary) — but that needs the id match above, which doesn't occur.

Verifying that a compression actually landed. After executing compress, the proxy emits a confirmation marker (📦 [ACP] Compressed …) as plain assistant text — but under sustained context pressure a model was observed writing that marker format itself without ever calling the tool (#717): 17 fake "compressions" over ~2 hours while real usage climbed to 89%. A marker line visible in the transcript is therefore not proof of persistence — verify with acp_status (block count increased, compressible-range start advanced) before trusting it. As a backstop, the proxy strips any marker-shaped line the model emits on its own and logs a [marker-echo] warning, and both the nudge and the injected prompt state explicitly that markers are proxy-emitted only.

Which do I need?

Pick by your client:

Client	Use
pi	billion-context-pi (in-process extension)
opencode (1.x / 2.x)	billion-context — bili opencode (launcher) or bili plugin install opencode (native, no launcher); standalone opencode-acp remains usable on 1.x. Full guide: OpenCode
omp	billion-context via bili omp (built-in plugin) or bili plugin install omp (self-spawning native plugin, no launcher)
dsh	bili dsh (launcher — full native plugin via --patch: tools, session-bound /acp, fetch intercept) or bili plugin install dsh ≡ dsh plugin --profile <name> add billion-context (one unified lane — pnpm-installs the package into each profile so dsh mounts the bundled patch layer; the bili form just drives dsh's own channel per profile and migrates legacy managed blocks)
kimi	bili plugin install kimi (self-spawning native plugin, no launcher — Kimi Code ≥ 2.0.0; per-session routing block in ~/.kimi-code/config.toml) or bili kimi (launcher, cert-MITM) or /bili/ prefix
claude	bili claude (launcher) or bili plugin install claude (native posture, #964 — managed settings block + session-owned proxy; see the notes below)
everything else (no context hook)	billion-context — bili <client> (launcher, preferred) or /bili/ prefix

Native mode vs standalone extensions. The host-native plugins (bili plugin install pi / opencode — they spawn the proxy inside the host process) and the standalone in-process extensions (billion-context-pi, opencode-acp) are mutually exclusive: both active means double compression. The installer makes the switch: bili plugin install pi replaces the legacy npm:billion-context-pi entry (with a reminder that a project-scope entry in <project>/.pi/settings.json from pi install -l lives outside the global settings), and bili plugin install opencode strips legacy opencode-acp entries from the global opencode.json — bare name, npm: alias, versioned (opencode-acp@stable), or path form, array or object shape; the original config is snapshotted to .bili-bak once. A project-local install (opencode plugin opencode-acp writes <project>/.opencode/opencode.json, not the global config) is not touched — remove it by hand; the installer note reminds you. As a runtime safety net for manual installs, the native entries set BILLION_CONTEXT_NATIVE=<host> synchronously at load so a standalone extension can stand down at action time — its own load-time BILLION_CONTEXT_PROXY check cannot see a proxy that native mode spawns asynchronously, and its /bili/ baseUrl check never sees the fetch-layer rewrite. On the pi side the marker needs billion-context-pi 0.1.72+ (the per-event re-check landed after 0.1.71); the pi-native entry additionally scans both pi settings files once its proxy is up and warns loudly when it spots a co-resident legacy entry the installer never saw — that warning is the only visible signal while an old billion-context-pi silently double-compresses.

Install

npm install -g billion-context

This installs the bili command (bili-proxy is kept as an alias).

Quickstart

Three ways to use it — pick one:

• Native plugin (no launcher): bili plugin install <client> — bili becomes a plugin inside the client; start the client as usual.
• Launcher (easiest): one bili <client> command brings up the proxy and the client together — no real config file is ever touched.
• URL change (persistent): prefix your client's baseURL with the proxy origin + /bili/.

Mechanism details behind these three options (plugin lifecycle, runtime-info protocol, injection priority) live in TECHNICAL-NOTES.md.

Option 1 — Native plugin (bili plugin install pi / omp / opencode / dsh / kimi)

The proxy lives inside the client: install once, then start the client exactly as you always do — no launcher command, no env vars, no fixed port, no URL edits. Supported today for pi, omp, opencode (1.x and 2.x), dsh and kimi:

bili plugin install pi          # registers a "billion-context" entry in pi's settings (npm form when bili itself was npm-installed)
bili plugin install omp         # registers an extensions entry in omp's config.yml (~/.omp/agent/config.yml)
bili plugin install opencode    # registers the plugin in opencode's real config + disables native auto-compaction
bili plugin install dsh         # runs 'dsh plugin --profile <name> add billion-context' for every existing profile
bili plugin install kimi        # writes $KIMI_CODE_HOME/plugins/managed/billion-context/kimi.plugin.json (+ installed.json record); per-session routing block lands in config.toml on first start (Kimi Code >= 2.0.0)
bili plugin remove <client>     # undo (dsh removes through the same channel; config snapshots go to .bili-bak)
bili plugin update [client]     # bring every lane's bili presence up to date, each through its own owner (see below)

Where a client has its own plugin channel you can also install natively, skipping bili commands entirely:

• dsh: dsh plugin --profile <name> add billion-context is the very command bili plugin install dsh drives per profile — same end state either way (pnpm into the profile, bundled patch layer mounted by dsh itself); remove through the same channel. See the dsh section below.
• opencode: add the bare npm name to your real config's plugin list — "plugin": ["billion-context"] (npm form only; a git checkout has no published entry). The package publishes exports["./server"] → dist/agent/opencode-native.js, so opencode loads it through its own Npm.add machinery and the plugin self-spawns exactly like the bili-installed form. Do the two things the bili installer would have done for you too: set "compaction": { "auto": false } in the same config (otherwise OpenCode's native auto-compaction double-compresses) and keep a manual backup of the file first.

For pi / omp / kimi / claude there is no client-side channel — bili plugin install <client> writes their config entries for you (kimi's declarative kimi.plugin.json + registry record, claude's managed settings block, …).

Single-writer: who owns which copy (#991)

Every bili presence on a machine has exactly one writer — the thing that installed it is the thing that updates it, and nothing else ever overwrites that copy in place:

Lane	Copy lives in	Updated by
global bili	npm global (npm i -g billion-context)	bili update / background auto-update
pi	pi's package manager (npm form)	pi update — bili never overwrites it
opencode	opencode's plugin dir	opencode's plugin manager — bili never overwrites it
dsh	each profile's pnpm store	global bili self-update re-runs dsh's plugin channel per profile (or dsh plugin add billion-context@latest); pnpm's hardlinked store must never be copied over in place
omp / claude / codex / kimi	no copy — entries point at the global bili install	they update together with the global copy

This is enforced in code, not just convention: the self-updater (src/update.ts → hostManagedInstall) detects install dirs under a pnpm virtual store (.pnpm) or a host agent tree (pi / opencode / dsh / kimi / omp homes) and skips them; installViaTarball refuses them structurally so direct callers cannot corrupt a store either. Mixing commands is fine (dsh plugin add ≡ bili plugin install dsh — same channel, same records); mixing writers is what the guard forbids. bili plugin update [client] is the one command that drives every lane through its own owner and prints the per-lane update path (bili plugin list shows the same per-lane channel).

At load the plugin spawns its own proxy (attaches to a healthy running one if present; a parent-pid watchdog tears it down when the client exits), rewrites model traffic to <proxy>/bili/<upstream-url>, registers compress / decompress / acp_status as native client tools (plugin mode), and reports the client's own model config to the proxy so compression budgets use the real window instead of a registry guess. Opt-out envs: BILI_NATIVE_PI=0, BILI_NATIVE_OMP=0, BILI_NATIVE_OPENCODE=0, BILI_NATIVE_DSH=0, BILI_NATIVE_KIMI=0. Full mechanics: TECHNICAL-NOTES.md.

Runtime-info protocol (#955). A native plugin reads the model config the client itself will use and pushes it to the proxy (per-request headers

• bootstrap report); the proxy prefers that truth over the models.dev registry / built-in table when resolving the context window. Protocol details, resolution order, and implementations: TECHNICAL-NOTES.md.

Notes:

• Native mode is mutually exclusive with the standalone in-process extensions (billion-context-pi, opencode-acp) — the installer swaps the entries and snapshots the original config (.bili-bak); migration details in the client table above (pi needs billion-context-pi 0.1.72+ to stand down cleanly).
• OpenCode: legacy opencode-acp sessions, the V1/V2 plugin shapes, and all caveats are consolidated in the OpenCode section.
• kimi reports runtime-info at bootstrap only (static custom_headers can't carry per-request window/model headers without going stale on model switch) and binds subagent conversations by per-call conversation_id — full mechanics in the "Kimi Code" section below.
• codex has a companion install too (an MCP shell), but it needs a running proxy — it is not native mode.
• claude also has a native posture (#964): bili plugin install claude writes a managed settings block (static /bili/ URL + SessionStart hook) plus an MCP shell pinned to a stable port — the proxy lives and dies with the session. Opt out with BILI_NATIVE_CLAUDE=0 (passthrough). Mechanics: TECHNICAL-NOTES.md.

Option 2 — Launcher (bili pi / bili codex / bili claude / bili omp / bili opencode / bili hermes / bili dsh / bili codebuddy / bili qoder / bili trae / bili jcode / bili kimi)

The launcher wraps a client in one command: it starts a proxy on an independent port (a fresh instance is always spawned — a port is never reused), then points the client at it — certificate-based MITM where the client honors proxy/CA env vars, or an isolated /bili/ config rewrite where it doesn't. No real config file is ever edited; the client's own config is READ to discover which HTTPS upstream hosts it talks to, and those hosts are whitelisted for MITM so the proxy can TLS-terminate exactly them and blind-tunnel everything else.

bili pi                               # launch pi through the proxy — file-free (#535): env + extension registerProvider, real ~/.pi untouched
bili codex                            # launch codex through the proxy
bili claude                           # launch claude through the proxy
bili omp                              # pi-style, file-free (#535): env + extension registerProvider + compaction cancel, real ~/.omp untouched
bili opencode                         # OpenCode (1.x & 2.x): full guide in the [OpenCode](#opencode) section below
bili hermes                           # file-free (#535): hermes proxy env (HTTPS_PROXY + HERMES_CA_BUNDLE) — https via CONNECT MITM, http via absolute-form forward proxy; real ~/.hermes untouched
bili dsh                              # deepseek-harness: full native plugin injected via --patch (#941) — compress/decompress/acp_status registered as real dsh tools, requests stamped with the dsh session id (plugin mode), /acp session-bound; non-loopback upstreams ride proxy envs (https MITM, http absolute-form), loopback keeps the overlay DSH_HOME (~/.dsh-bili) rewrite (#535), built-in deepseek route via DEEPSEEK_BASE_URL; dsh native auto-compaction disabled (compaction-basic auto:false)
bili codebuddy                        # Tencent CodeBuddy Code CLI: CODEBUDDY_BASE_URL /bili/ rewrite (OpenAI chat completions wire), budget aligned via CODEBUDDY_AUTO_COMPACT_WINDOW; real ~/.codebuddy untouched
bili qoder                            # qoder: model endpoint is hardcoded https (no /bili/ rewrite possible) — cert-MITM via HTTPS_PROXY + NODE_EXTRA_CA_CERTS, default model hosts whitelisted (#653)
bili trae                             # Trae CLI (ByteDance, closed Go binary, no base-URL override) — cert-MITM via HTTPS_PROXY + SSL_CERT_FILE, model host from TRAE_CLI_API_HOST or the default enterprise gateway (#655)
bili jcode                            # jcode (Rust agent harness) — env-only cert-MITM launch: HTTPS_PROXY + SSL_CERT_FILE, model host api.z.ai whitelisted, local loopback providers stay direct via NO_PROXY
bili kimi                             # Kimi Code CLI (Moonshot): honors standard proxy envs for all traffic EXCEPT an unconditional loopback bypass — non-loopback https via cert-MITM (HTTPS_PROXY + NODE_EXTRA_CA_CERTS/SSL_CERT_FILE), non-loopback http via absolute-form forward proxy; provider/model hosts from ~/.kimi-code/config.toml (KIMI_CODE_HOME respected) or the managed OAuth endpoints when none declared; loopback endpoints inventoried with a manual /bili/ prefix hint (#757)
bili pi --mitm-domain api.foo.com     # add a domain to the MITM whitelist

Option 3 — URL change (/bili/ prefix)

Start the proxy:

bili

Then just prefix your client's existing baseURL with http://localhost:8787/bili/. The full upstream URL is embedded in the path, so the proxy knows where to forward without any config:

client baseURL before:  https://api.openai.com/v1
client baseURL after:   http://localhost:8787/bili/https://api.openai.com/v1

That's it — put your real API key in the client config as usual (the proxy passes it through untouched). Context windows (gpt-5.1-codex=400K, glm-5.2=1M, claude-opus-4=200K, …) are looked up from models.dev automatically.

For per-client configuration examples (OpenCode, Codex, Pi, login-client MITM, …) see the web UI guide at http://localhost:8787.

Verify. With the proxy running and your config saved, check it answers and that your first real request shows compression activity in the log:

# Health check (proxy up + where it forwards)
curl -s http://localhost:8787/__bili/health
# → {"ok":true,"upstream":"https://api.anthropic.com"}

# Live session stats (after a real request)
curl -s http://localhost:8787/__bili/stats

Then send one message from your client and watch the log (~/.local/state/billion-context/bili.log, also printed to stderr). You should see a processTurn line per request, and once the conversation grows, [acp-usage] round N input=X cached=Y (cache hit Z%) + a compress event.

dsh (deepseek-harness)

Two lanes, same plugin (#941):

• Launcher: bili dsh injects the full native plugin through a --patch overlay (~/.dsh-bili/.bili-acp.patch.yml) — every profile boots with the bili tools registered natively, model requests carry x-bili-plugin + the dsh session id (plugin mode), and /acp is session-bound. dsh's native auto-compaction is disabled in the same patch (compaction-basic → auto: false); manual /compact stays available.
• Profile install (no launcher) — one lane (#966): bili plugin install dsh runs dsh plugin --profile <name> add billion-context for every existing profile — pnpm installs the package into each profile's own node_modules, and dsh mounts the bundled patch layer (dsh.bundle.patch.yml) automatically. The spec follows how bili itself was installed (#925): an npm-form install passes the registry name, a checkout/dev build passes its absolute path (a link: dependency, so local work stays live). Legacy managed blocks (# bili begin / # bili end, written by pre-#966 installs) are stripped on install and remove — user entries and comments survive, an emptied file gets its placeholder [] back. Run dsh once in each profile first so the profile dirs exist. The plugin spawns its own proxy at load (attaches to a healthy one instead of doubling; parent-pid watchdog), rewrites model-API traffic to <proxy>/bili/<upstream-url> via a global fetch patch, registers the manifest tools verbatim, and gates plugin-mode headers on tool readiness (round 1 rides wire mode). Opt-out: BILI_NATIVE_DSH=0. Remove with bili plugin remove dsh or dsh plugin --profile <name> remove billion-context — both go through the same channel. Registry installs require a published release that carries dsh.bundle.patch.yml.
• Auto-update keeps profiles in lockstep: after a global self-update, bili scans ~/.dsh/profiles/*/package.json and brings any registry-pinned billion-context dependency back to the new global version, so the loaded plugin and the proxy never drift apart again (#953); profiles pinned to a local source are left alone. The refresh is best-effort and never fails the update itself.

Under a bili dsh launch the plugin ATTACHES to the launcher's proxy (no second spawn). Raw upstream URLs rewrite to <proxy>/bili/<url> like spawn mode (a loopback proxy target is never proxied, so the MITM envs are simply bypassed); already-routed /bili/-prefixed requests pass through untouched except for header stamping. Known limitation: manual /compact has no dsh-side event hook, so its boundary is left to the kernel's natural ingest diff (auto-compaction is off, so this is rare).

Kimi Code (Moonshot)

Three aligned modes: bili kimi (launcher, cert-MITM — Option 2), /bili/ URL prefix, and native plugin mode (bili plugin install kimi, #963). Kimi Code v2's plugin system is declarative only (kimi.plugin.json: MCP servers, hooks, skills — no in-process JS execution), so bili cannot patch the client's fetch stack like it does for pi/opencode/dsh. Instead the plugin ships two small node scripts that do the work around the client:

• Install: bili plugin install kimi writes $KIMI_CODE_HOME/plugins/managed/billion-context/kimi.plugin.json declaring a stdio MCP server (node <root>/dist/kimi/native-mcp.js) plus a SessionStart hook (node <root>/dist/kimi/bootstrap-hook.js, 30 s timeout), and registers the plugin in $KIMI_CODE_HOME/plugins/installed.json. The installer requires kimi --version ≥ 2.0.0 and refuses below that (the launcher still works either way). Remove with bili plugin remove kimi (managed dir + registry record + config restore).
• Per-session bootstrap: kimi spawns the MCP server as a direct child for each session; at startup it attaches to a healthy proxy (BILLION_CONTEXT_PROXY) or spawns its own on an ephemeral port, then rewrites the client's routing with an idempotent, line-surgical managed block in ~/.kimi-code/config.toml: an own provider [providers.bili] (base_url = http://127.0.0.1:<port>/bili/<upstream>, cloning the active provider's oauth / api_key reference verbatim), a [models.bili-kimi] alias, and a top-level default_model redirect with the previous value recorded inside the block. The original file is snapshotted to config.toml.bili-bak once; every write happens under a mkdir lockfile and user content outside the block is never touched. Kimi's config hot-reload applies the change to live sessions. The SessionStart hook runs the same bootstrap opportunistically (attach-only — it never spawns); its non-blocking race is tolerated by design: round 1 may ride direct/wire mode, and the invariant is never pointing base_url at a dead port.
• Plugin-mode stamping: the block gains custom_headers = { x-bili-plugin = "kimi" } ONLY after the ACP tool list has been verified against the live proxy manifest — until then traffic rides wire mode. Because custom_headers are static per provider they cannot carry per-request window/model headers without going stale on model switch; the runtime-info report therefore happens at bootstrap only (model + context window + max output from the client's own config whenever present).
• Watchdog & lifecycle: the MCP child probes the proxy every 30 s. In attach mode it waits forever (it never touches a user-owned proxy); in spawn mode a dead proxy is respawned and the routing rewritten to the new origin. If recovery fails, the managed block is removed so traffic degrades back to direct upstream rather than hitting a dead port. When a session ends, kimi kills the MCP child and the parent-pid watchdog tears down the spawned proxy. Multiple concurrent TUIs share the first-spawned proxy; when it goes away the remaining sessions respawn and re-route automatically.
• Known limitations: subagent conversations get their own derived proxy sessions (kimi exposes no stable session id; tool calls bind via the per-call conversation_id argument), and kimi's native auto-compaction is NOT pushed out — ACP compression simply fires first, as in launcher mode. Opt-out: BILI_NATIVE_KIMI=0.

Client uses http.proxy (CONNECT) but nothing compresses

Some clients (VS Code-based IDEs: CodeBuddy, Cursor, Windsurf, …) only offer an HTTP proxy setting (http.proxy, codingcopilot.httpProxyURL, …) — no model base-URL to rewrite. Such clients send CONNECT <model-host>:443 through the proxy instead of plain /bili/… requests. That path is only decrypted when the model host is on bili's MITM whitelist; otherwise bili blind-tunnels the TLS bytes (opaque relay) and can never see — or compress — the model requests (#897).

This failure mode is now loud instead of silent:

• a one-time BLIND TUNNEL WARNING per target host in the log, with the fix steps;
• blindTunnels (count + exact target hosts) in curl -s http://localhost:8787/__bili/health and /__bili/stats (loopback-only);
• an UNDECRYPTED TRAFFIC (instance-level) section in acp_status output while such tunnels exist.

To actually compress such a client: add its model domain to "mitm".domains in billion-context.json (e.g. "mitm": { "domains": ["copilot.tencent.com"] }) or via BILI_MITM_DOMAINS, restart bili, and make the client trust bili's root CA (NODE_EXTRA_CA_CERTS=~/.local/share/billion-context/ca/root-ca.pem for Node-based clients, or the client's own CA-path setting). The /bili/ prefix trick does not apply here — there is no URL to change. Details: CONFIGURATION.md → MITM.

OpenCode

One bundled plugin serves both OpenCode generations: the agent file keeps the V1 server() export alongside the V2 setup(), so hosts ≥ 1.18.29 load the V1 shape and 2.x hosts load the V2 setup(). The standalone opencode-acp extension is V1-only and does not load under 2.x — for OpenCode 2.x, billion-context is the recommended context manager. Everything below is verified end-to-end on @opencode/cli 2.0.3 (V1 lane: 1.14.46 and 1.18.31).

Path	Command	When
Launcher (easiest)	bili opencode	one command brings up proxy + client; real config untouched
Native (no launcher)	bili plugin install opencode	self-spawning plugin in your real config; start opencode as usual
Pure proxy (fallback)	baseURL /bili/ prefix	no plugin — wire-level tool injection

Launcher — bili opencode

HTTPS rides cert-MITM, HTTP a temp opencode.json clone with /bili/ (JSONC comments accepted, merged the way opencode itself merges them; relative local plugin specs re-anchored to absolute paths in the clone — opencode resolves them against the declaring config file's dir, #826). Host generation is detected with a --version probe (failed probe defaults to 1.x): on a 2.x host the built-in V2 plugin (dist/agent/opencode.js) is injected as a temp wrapper directory whose index.js re-exports the plugin file (2.x rejects bare file paths in the config plugin array); 1.x hosts get the bare file path.

What the plugin does (both generations): registers the bili tools natively in-host — compress / decompress / search_context / acp_status (+ absorb) — and stamps the proxy headers on every outgoing provider request, including context-window / max-output read from the host's own model catalog (ctx.catalog.model.list(), refreshed every 60s) and reported to the proxy as runtime-info (#955) — compression runs in plugin mode with no wire-level tool injection. Native auto-compaction is disabled automatically (compaction.auto: false). Every registration is defensive (optional chaining): on any 2.x build where a seam is missing or never fires, the plugin stays inert and the session transparently runs in plain proxy mode instead of breaking — observed across adjacent dev builds whose API surfaces differ from each other (#754 review probes).

1.x specifics (verified 1.14.46 + 1.18.31): the V1 .server() hooks rewrite every provider options.baseURL to <proxy>/bili/… in-process and set compaction.auto: false; chat.headers stamps the plugin headers per request; tool registers the bili tools with real zod shapes (zod is a runtime dependency — when it cannot be resolved the plugin degrades to rewrite-only). Providers without an explicit baseURL (SDK defaults, e.g. bare @ai-sdk/openai → api.openai.com) are caught by a global fetch patch (log: v1: fetch patch installed) — idempotent, passes /bili/-wrapped URLs through untouched; verified including the OpenAI Responses endpoint.

Native (no launcher) — bili plugin install opencode

Registers a self-spawning plugin in your real opencode config and sets compaction.auto: false; afterwards plain opencode works as-is. No MCP face is added by default (the native plugin already provides the bili tools, session-bound); pass --with-mcp to add one — the entry then carries no origin pin, so it survives the plugin's ephemeral-port proxy restarts (#926). Entry form depends on how THIS bili was installed: an npm install writes the bare package name ("plugin": ["billion-context"]) — the package publishes exports["./server"] → dist/agent/opencode-native.js, so opencode loads it through its own Npm.add machinery; zero absolute paths, portable. (That exact bare-name entry doubles as a hand-install without bili — see Option 1.) A git checkout / dev build falls back to a local shim dir (<configDir>/plugins/billion-context/index.js → this checkout's dist/agent/opencode-native.js) — machine-local by construction; re-running install from an npm install migrates the entry back to the bare name.

At load the plugin bootstraps its own proxy (attaches to a healthy instance instead of doubling; parent-pid watchdog kills it when opencode exits), routes model-API traffic to <proxy>/bili/<upstream-url>, and exposes the same native bili tools as launcher mode — no fixed port, no env var, no launcher. Opt-out: BILI_NATIVE_OPENCODE=0. If no proxy can be made healthy, requests go direct (uncompressed) with a one-time warning and recover automatically. Under a bili opencode launch this entry is skipped entirely (the launcher owns the proxy).

Pure proxy (no plugin)

Point the provider baseURL at the proxy like any other client:

{
  "provider": {
    "myprovider": {
      "npm": "@ai-sdk/openai-compatible",
      "options": {
        "baseURL": "http://localhost:8787/bili/http://upstream.example/v1",
        "apiKey": "sk-any"
      }
    }
  }
}

Note: 2.0 AI-SDK providers require an apiKey field even for local endpoints that never check it — set any non-empty value.

Status: /acp and acp_status

The /acp panel is session-bound in all modes, and the acp_status tool is its in-host equivalent everywhere. On 2.0.x stable, where the command editor supports adding entries (editor.add), the V2 plugin additionally registers an /acp slash command — rendered as a synthetic non-model message, panel-first like the acp_status tool; on older shapes the registration stays inert. Note opencode run mode dispatches no slash commands at all (they pass through to the model) — use the TUI.

Legacy opencode-acp sessions (#920)

On 1.x hosts, pre-migration opencode-acp sessions keep working under both lanes: the launcher strips the opencode-acp entry from its temp config clone (the host never loads it armed), and each lane absorbs the installed package (imported directly from node_modules — .opencode/node_modules, project node_modules, global npm root, or opencode's config-scope modules, first hit wins). A session is legacy iff opencode-acp's persisted state file exists (<XDG_DATA_HOME>/opencode/storage/plugin/acp/<sessionID>.json, or the dir from storagePath in acp.jsonc):

• Legacy session — compression runs through the absorbed opencode-acp (its own refs and block store keep working: compress / decompress / search_context / acp_status / acp_context_recap all execute in it). Its model requests carry x-bili-plugin-bypass: 1; the proxy forwards them VERBATIM — no wire injection, no nudge, no session binding.
• New session — bili owns it: tool calls forward to the proxy's plugin endpoints (plugin mode). The executor routes by session lane, so a new session's compress reaches the proxy while a legacy session's reaches opencode-acp. acp_context_recap has no proxy counterpart — on new sessions the proxy answers with its unknown-tool message.

/acp and /dcp route the same way. Adoption of new sessions into opencode-acp's registry is prevented by gating its transforms (system / messages / text.complete) on the legacy predicate. Degradation: when the package is absent or fails to import (or isn't v1), bili runs alone and legacy sessions behave as read-only archives (old tags render, decompress returns [Block … not found], new refs restart from m00001).

Caveats

• The 2.x line publishes as npm package @opencode/cli, and its plugin API surface is still moving between builds (adjacent dev-channel builds expose different ctx shapes) — the hook/tool details above are version-specific observations, not a stable contract.
• Design note: the V2 plugin is a thin protocol client (no acp-kernel inside) because the proxy stays the single compression authority — that eliminates kernel-version drift between agent and proxy; it does not rely on the plugin API being unable to mutate context (that capability varies by 2.x build).

Running the proxy

Flags

bili --port 9000              # change listen port
bili --host 0.0.0.0           # listen on all interfaces (see host note below)
bili --debug                 # verbose logging (also: set "debug": true in config)
bili --passthrough           # forward without compression (smoke-test mode)
bili --config ~/my-bili.json # use a different config file
bili update                  # check & install a newer version now (bypasses throttle)
bili --no-auto-update        # disable self-update for this run

Flags override env vars and the config file. bili --help lists them all.

Remote agents (--host)

By default the proxy binds 127.0.0.1 and only accepts loopback connections. To serve agents on other machines, bind a non-loopback host:

bili --host 0.0.0.0           # all interfaces (or use your LAN IP)

• Remote agents point their model baseURL at http://<this-host>:<port>/bili/….
• MITM-mode CONNECT then also accepts remote clients — for whitelisted model hosts only. Blind tunnels to arbitrary hosts stay loopback-only, so the proxy can never be used as an open relay.
• The /bili/<absolute-url> tunnel has destination admission (#409): the proxy itself and link-local/metadata addresses are always denied; loopback/private destinations are allowed for local clients (self-hosted upstreams) and denied for remote clients unless listed in BILI_TUNNEL_ALLOWED_HOSTS (host or host:port, comma-separated) — a remote peer must not use the proxy as an SSRF pivot into your LAN, and the management plane is unreachable through the tunnel even via NAT hairpin (tunneled requests carry an internal x-bili-tunnel marker that /__bili/ rejects).
• There is no authentication: only do this on a trusted LAN or behind a firewall. The /__bili/ management endpoints remain loopback-only.
• A startup [security] warning reminds you of the above.

Debugging

Three ways to enable verbose logging (priority: flag > env > config):

1. CLI flag (quickest): bili --debug
2. Env var: ACP_DEBUG=1 bili
3. Config file: "debug": true in billion-context.json

Verbose mode logs every processTurn (tag counts, token usage), the nudge decision (growth/usage/pendingT1/shouldInject), client headers, and SSE rewrites.

Log file

All logs are tee'd to a file by default: ~/.local/state/billion-context/bili.log (XDG state dir). They also still print to stderr so a foreground bili start shows them in the terminal.

# Config:  "logFile": "/custom/path.log"
# Env:     ACP_LOG_FILE=/custom/path.log   (or ACP_LOG_FILE=off to disable the file)

The file auto-rotates at 10 MB (renamed to bili.log.old). Cache-hit stats per request are logged as [acp-usage] round N input=X cached=Y (cache hit Z%) so you can measure prefix-cache health directly from the log.

Self-update

The proxy checks npm for a newer version on startup and every 3 minutes. When a newer version is found it installs it globally (npm install -g) and logs a notice — restart bili to pick up the new version.

Disable permanently via config ("autoUpdate": false) or env (ACP_AUTO_UPDATE=0).

Configuration

The full configuration reference — config file location, top-level keys, providers, compression tuning, environment variables — lives in CONFIGURATION.md.

Upstream proxy (firewall / GFW)

If the proxy's own outbound connections to a model provider are blocked (e.g. api.openai.com from inside the GFW), configure an upstream proxy (the local v2rayA / clash HTTP port) so the proxy reaches the provider:

{
  // Global default: ALL providers route through this proxy
  "proxy": "http://127.0.0.1:20172",
  "providers": {
    "https://api.openai.com/v1": {
      // Per-URL overrides global (use a different proxy for this host)
      "proxy": "http://127.0.0.1:20173",
      "models": { "gpt-5": { "context": 400000 } }
    },
    "https://open.bigmodel.cn/api/anthropic": {
      // Empty string = explicitly DIRECT, overriding the global proxy
      "proxy": "",
      "models": { "glm-5.2": { "context": 1000000 } }
    }
  }
}

Rules:

• Per-URL proxy has the highest priority for its matching provider URL.
• Remaining priority is BILI_UPSTREAM_PROXY → Web UI manual proxy → top-level proxy → HTTPS_PROXY / HTTP_PROXY / ALL_PROXY → Windows system proxy → direct.
• Empty string "" means explicitly direct (override-and-disable).
• Auto mode honors NO_PROXY and the Windows proxy bypass list for environment/system fallbacks. A proxy pointing back to bili's own local port is ignored or rejected to prevent a loop.
• HTTP and HTTPS proxy origins are supported. SOCKS5 is not supported yet.
• Both outbound paths are covered: /bili/ path-mode (fetch) AND MITM CONNECT tunnels (the proxy's connection to the real upstream goes through the HTTP CONNECT proxy).
• The auto-updater's own egress (npm registry check + tarball download) uses the same decision for its hosts, so bili update and auto-update work on hosts where npm is only reachable through the proxy (#609).

Env override: BILI_UPSTREAM_PROXY=http://127.0.0.1:20172 (higher priority than the config file). On Windows, common Clash/Mihomo static system proxies are discovered automatically; the Web UI shows the effective source and any PAC URL detected in Internet Settings.

MITM vs /bili/ — distinguishing the key scheme. A login client (ZCode via MITM) and an API-key client can both hit the same host (open.bigmodel.cn). To let their config differ, MITM traffic uses a mitm:// scheme in the lookup key while /bili/ traffic uses the real https://:

Client	Lookup key example
ZCode (MITM, login)	mitm://open.bigmodel.cn
API-key client (/bili/)	https://open.bigmodel.cn/api/anthropic

So you can give ZCode its own proxy without affecting API-key clients:

{
  "providers": {
    "mitm://open.bigmodel.cn":            { "proxy": "http://127.0.0.1:20173" },
    "https://open.bigmodel.cn/api/anthropic": { "proxy": "http://127.0.0.1:20172" }
  }
}

Wire-compat role rewrite (compat.roles)

Some upstreams reject the developer role newer codex clients send on the Responses API (400 Invalid role: developer). compat.roles maps roles to what the upstream accepts — applied at the forward boundary to the final openai/responses body (client-sent roles and bili's own injected prompt alike), global or per-provider, default off = byte-for-byte:

{
  "compat": { "roles": { "developer": "system" } },
  "providers": {
    "https://picky.example.com": { "compat": { "roles": { "developer": "user" } } }
  }
}

No configuration needed for the common case. When an upstream answers a request with 400 Invalid role: …, bili auto-rewrites the offending role to system, retries the request once, and — if the retry succeeds — remembers the mapping for that session only (nothing is written to your config). Later requests in the session skip the 400 round-trip. The log line printed when the auto-fix fires includes a copy-paste per-provider snippet if you want the mapping permanently.

How sessions work

The proxy needs a stable per-conversation identifier to isolate compression state across concurrent users/accounts. It derives one from four dimensions (see src/session-id.ts): protocol × upstream origin × API key × conversation. The first three prevent cross-account / cross-provider bleeding; the conversation dimension comes from whatever the client sends.

Clients differ in what they send:

Client	Sends conversation id?	Source	Safety
Codex (0.147+)	✅ yes	body.session_id (per-conversation UUID)	✅ safe
OpenCode	✅ yes	x-session-affinity header (ses_…)	✅ safe
pi	❌ no	nothing	⚠️ collision risk

When the client sends an explicit id, the proxy uses it directly. When it does not (pi), the proxy falls back to hashing the first user message — so two conversations that start with the same opener collapse onto the same session. This does not corrupt data (per-message refs use a separate content fingerprint that stays stable), but it can skew nudge/compression timing and occasionally over-eagerly reap a block. It is self-healing: the worst case is reduced compression efficiency, never data loss.

For upstream sticky-routing, when the client sends no session header the proxy synthesizes one (x-session-id: ses_<hash>) so cache pools / load balancers still get a stable key.

Recommendation: Codex and OpenCode are safe to run many concurrent conversations through the proxy. pi is fine for a single agent, but is not recommended for many concurrent conversations because of the collision risk — until pi grows its own session-id signal. For pi multi-agent use, pass an explicit x-acp-session header per conversation to avoid collisions.

Windows: exclude the sessions dir from antivirus (#362)

The proxy persists each session's compression state to the sessions dir (%USERPROFILE%\.local\share\billion-context\ by default) and rewrites the file every turn of a long session. Persisted per session: the compression state (block summaries), the compressed originals cache (blockContents, what bili export --full recovers), and a bounded folded-view snapshot of the recent conversation (newest BILI_PERSIST_TAIL_TOKENS tokens, default 16k) — the raw full history is never duplicated on disk (#401). On Windows, real-time antivirus (Windows Defender), the search indexer, or a sync tool (OneDrive) can lock that directory mid-write, so the rename fails with EPERM and every persist for that session fails until the lock clears.

When the same session fails N consecutive writes (default 5), the proxy logs a one-time, actionable alert naming the directory to exclude. To fix it at the root: add %USERPROFILE%\.local\share\billion-context\ to your antivirus exclusions (Windows Defender: Settings → Virus & threat protection → Manage settings → Exclusions → Add an exclusion → Folder) and make sure no sync tool (OneDrive / Dropbox / …) is syncing that path. Full steps in CONFIGURATION.md.

Status

Early. Protocol handling and compression work against mock tests (500+ passing). Real-model integration testing is the next milestone. Expect rough edges.

Client-side plugins for pi / omp / opencode ship inside billion-context (dist/agent/*.js) for the cooperative-proxy path. See the "Which do I need?" section above for how billion-context, the standalone billion-context-pi, and opencode-acp relate.

Community

QQ group — one shared group for all three projects (billion-context, billion-context-pi, opencode-acp): 1056132097

License

MIT