T3 Chat Router & Wire Protocol Research: t3router & pi-t3chat (2026)

This document provides the line-verified reverse-engineering specification of vibheksoni/t3router (~/dev/t3router, commit 5314bbbf0af66e724e3e07ffd458ef5919d1eed1) and vibheksoni/pi-t3chat (~/dev/pi-t3chat, commit b39873245362c33f68a9a3e044423f69769069f9). It documents the POST https://t3.chat/api/chat wire contract, Chrome 136 TLS impersonation (rquest::Impersonate::Chrome136), WorkOS x-workos-session automatic rotation, the /assets/*.js regex bundle scraper (eval_js_number vs parseFloat), all 6 tRPC endpoints, poll_credit_delta, ToolCallTranslator, ToolRefusalDetector, and the 3-tool lazy MCP wrapper (list_mcps, list_mcp_tools, call_mcp).

1. Repository & Module Inventory

1.1 vibheksoni/t3router (~/dev/t3router — Rust 2021)

• src/lib.rs & src/t3/mod.rs:1-10: Declares pub mod client; pub mod config; pub mod history; pub mod message; pub mod models; pub mod repl; pub mod session; pub mod usage; (with zero pub use re-exports in mod.rs).
• src/t3/config.rs:1-58: Defines ReasoningEffort (Low, Medium, High, Default = Medium) and Config (include_search: bool, reasoning_effort: ReasoningEffort).
• src/t3/client.rs:174-792: Defines ChatResponse (message: Message, thread_id: String, model: String, credits_before: Option<f64>, credits_after: Option<f64>, credits_deducted: Option<f64>, finish_reason: Option<String>), SseAccumulator, poll_credit_delta, and Client (new, warmup, init, refresh_session, send, send_stream, send_with_credits, send_with_credits_stream, send_with_image_download, finalize_credits, parse_response, new_conversation, resume_conversation, append_message, get_messages, clear_messages, download_image, get_thread_id).
• src/t3/models.rs:1-665: ModelsClient, ModelInfo, ModelCost, AttachmentSupport, ModelStatus, ModelBenchmarkEntry, BenchmarkMetric, parse_models_from_bundle, eval_js_number.
• src/t3/usage.rs:1-415: UsageClient, CustomerData, SubscriptionData, PricingData, CreditPack, TopUpInfo, SessionInfo (session_id, created_at, expires_at, ip_address, user_agent), UsageSummary, extract_trpc_result.
• src/t3/session.rs:1-114: SavedSession, SavedMessage, default_session_path() (reads T3CHAT_SESSION_PATH before falling back to ~/.t3chat_session.json), save_session(&SavedSession), load_session().
• src/t3/repl.rs:36-45, 176-254: Interactive REPL supporting /help, /new, /resume, /save, /model [name], /credits, and /quit (alias /exit). (Implementation note: repl.rs:250 calls poll_credit_delta a second time after client.send_with_credits_stream already invoked it at client.rs:744.)
• src/bin/t3chat.rs: Full CLI binary supporting --list-models, --status, --benchmarks, --usage, --credits, --effort, --search, --save, --resume, and interactive REPL mode.

1.2 vibheksoni/pi-t3chat (~/dev/pi-t3chat — TypeScript)

• index.ts:118-191: Pi coding-agent extension entrypoint registering flags --t3chat-login and --t3chat-cookies and slash commands /t3chat-status, /t3chat-logout, and /t3chat-refresh.
• auth.ts: Playwright browser login (loginWithBrowser), ~/.pi/agent/t3chat-auth.json persistence (chmod 0o600), and refreshSession (auth.getActiveSessions).
• catalog.ts:147-276: Exports getCachedCatalog (L262) and clearCachedCatalog (L276), wrapping internal fetchCatalog (L231, scanning up to 12 JS chunks in parallel via chunkPaths.slice(0, 12)).
• config.ts:1-28: Exports type ReasoningEffort, interface ChatConfig, defaultConfig(), and buildConfigObject().
• chat.ts:59-108 & sse.ts:1-95: chat.ts defines T3_BASE_URL = "https://t3.chat", mapSSEEvent (L85–108), and streamT3Chat; sse.ts defines SSEEvent (text-delta, reasoning-delta, finish-step, finish, error) and parseSSEStream.
• tools.ts:1-310: ToolRegistry, ToolCallTranslator, ToolCallDeltaAccumulator, and ToolRefusalDetector.
• mcp.ts:1-210: Lazy MCP wrapper (list_mcps, list_mcp_tools, call_mcp, MAX_WRAPPER_ROUNDS = 6).
• proxy.ts:40-48, 704-733: Localhost OpenAI-compatible HTTP proxy (T3_PROXY_HOST = "127.0.0.1", T3_PROXY_PORT = 42101, fallback to server.listen(0) on EADDRINUSE) exporting startProxy, stopProxy, PROXY_SECRET (32-byte random hex verified via crypto.timingSafeEqual), proxyCredentials, and setProxyCredentials.
• tokens.ts, usage.ts, log.ts:1-32: log.ts exports setNotifier, logInfo, logWarn, logError with a pre-session _buffer queue.

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2. POST https://t3.chat/api/chat Wire Contract & WorkOS Rotation

• TLS Fingerprint (t3router/src/t3/client.rs:205): Uses rquest::Impersonate::Chrome136 to satisfy Cloudflare JA3/JA4/HTTP2 checks.
• Automatic Session Rotation (client.rs:235-252 & pi-t3chat/auth.ts:112-160): Calls GET https://t3.chat/api/trpc/auth.getActiveSessions?batch=1&input=%7B%220%22%3A%7B%22json%22%3Anull%2C%22meta%22%3A%7B%22values%22%3A%5B%22undefined%22%5D%7D%7D%7D. If the response carries x-workos-session or set-cookie: wos-session=..., the client hot-swaps wos-session in memory and persists it.
• Request Payload (POST https://t3.chat/api/chat):

  {
    "messages": [
      {
        "id": "<uuid-v4>",
        "role": "user",
        "parts": [{ "type": "text", "text": "..." }],
        "attachments": []
      }
    ],
    "threadMetadata": { "id": "<thread-uuid-v4>" },
    "responseMessageId": "<response-uuid-v4>",
    "model": "claude-sonnet-4-6",
    "convexSessionId": "<session-uuid-v4>",
    "modelParams": {
      "reasoningEffort": "medium",
      "includeSearch": false
    },
    "preferences": {
      "name": "",
      "occupation": "",
      "selectedTraits": [],
      "additionalInfo": ""
    },
    "userInfo": { "timezone": "America/Los_Angeles" },
    "isEphemeral": false
  }

• SSE Event Stream (client.rs:60-170, sse.ts:1-95): Emits data: {"type":"reasoning-delta","delta":"..."}, data: {"type":"text-delta","delta":"..."}, data: {"type":"finish-step",...} (mapped to null by mapSSEEvent in chat.ts:104-105), data: {"type":"finish","finishReason":"stop"}, and data: [DONE].

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3. Dynamic JS Bundle Scraper & tRPC Procedures

3.1 /assets/*.js Scraper Differences (t3router/src/t3/models.rs vs pi-t3chat/catalog.ts)

Both scrapers fetch https://t3.chat/, extract /assets/[^"]+\.js[^"]*, locate the chunk containing usdCostPerToken and modelToInternalId, and extract model entries:

• t3router/src/t3/models.rs:437-662:
  • eval_js_number (L647–662) explicitly evaluates /1e6 and /1e3 division expressions in usdCostPerToken: { input: 3/1e6, output: 15/1e6 }.
  • Handles both features: new Set([...]) and features: [...] (L437–449).
• pi-t3chat/catalog.ts:147-253:
  • Scans up to 12 chunks in parallel (chunkPaths.slice(0, 12) via Promise.all), filters out image-only models (features.every(f => f === "images")) and retired models (retiredOn), and parses usdCostPerToken with parseFloat(costMatch[1]) (which drops /1e6 suffixes).

3.2 tRPC Endpoints & Header Differences (t3router/src/t3/usage.rs vs pi-t3chat/usage.ts)

1. auth.getActiveSessions: Client::refresh_session (client.rs:237-246) sends trpc-accept: application/jsonl, whereas UsageClient::get_active_sessions (usage.rs:397-408) sends x-trpc-source: web-client without trpc-accept.
2. getCustomerData: Returns creditsRemaining, totalCredits, NextCreditRefill, TopUpInfo.
3. getSubscriptionData: t3router (usage.rs:367-368) sends x-trpc-batch: true + trpc-accept: application/jsonl; pi-t3chat (usage.ts:204) calls trpcCall(cookies, "getSubscriptionData", null, false).
4. getPricingProducts: t3router (usage.rs:309) sends {"0":{"json":{"sessionId":null},"meta":{"values":{"sessionId":["undefined"]}}}}; pi-t3chat (usage.ts:214) sends {"0":{"json":null,"meta":{"values":["undefined"]}}}.
5. getModelStatuses & getAllModelBenchmarks (t3router/src/t3/models.rs:212-345): Returns live status (operational, degraded, outage) and benchmark scores across Artificial Analysis, LiveBench, SweBench, SnitchBench, SkateBench, etc.

3.3 Post-Turn Credit Delta Polling (t3router/src/t3/client.rs:770-792)

• poll_credit_delta loops for attempt in 0..8, sleeping 200ms only when attempt + 1 < 8 (7 sleeps = 1.4s max sleep). If none of the 8 loop checks observes (before - after).abs() > 0.000_1, line 786 performs a 9th unconditional usage_client.get_balance().await.ok() call and returns (final_after, final_after.map(|after| before - after)).

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4. Coding-Agent Tool Emulation, Refusal Auto-Correction & Lazy MCP (pi-t3chat)

• ToolCallTranslator (tools.ts:45-210): Serializes OpenAI tool definitions into system prompt instructions requiring ```tool:<exact_tool_name>\n{...}\n``` fenced blocks.
• ToolRefusalDetector (tools.ts:265-305): Detects false refusals in the first 350 characters when tools.length > 0, toolCallsFound === 0, and text.length < 700 using two exact regexes (tools.ts:270-271):
  • REFUSAL_RE = /\b(can't|cannot|can not|don't have|do not have|unable to|not able to|no access|without access|can't actually|cannot actually)\b/i
  • CAPABILITY_RE = /\b(tool|terminal|shell|command|run|execute|file|filesystem|browse|browser|web search|search|calendar|schedule|environment)\b/i
  • When both match (!retriedRefusal), proxy.ts discards the refusal and retries once with a corrective system reminder listing the available tool names.
• Lazy MCP Wrapper (mcp.ts:1-210): Collapses all mcp__<server>__<tool> tools into 3 lightweight meta-tools (list_mcps, list_mcp_tools, call_mcp) resolved locally in proxy.ts up to MAX_WRAPPER_ROUNDS = 6.