taodengandClaude <claude-opus-4-8> <noreply@anthropic.com>
8405e30d0e
Maintainer directive (2026-07-18): the hand-set 150,000-char default (~37.5k English
tokens) is obsolete in the long-context era. Instead of a new constant that would rot
the same way, the default now derives from the SPOT:
MAX_PROMPT_CHARS (default) = max(models.json contextWindow) x 3 chars/token
= 200000 x 3 = 600,000 chars today (~150-200k tokens)
x3 is the CJK-safe multiplier: English runs ~4 chars/token, CJK ~1-1.5, so a
1M-token-derived char cap would let CJK text sail past the model's real window into
an upstream rejection; at x3 the cap fires at roughly the model's true window and OCP
truncates gracefully (tail-first) instead. Pure derivePromptCharBudget() in
lib/prompt.mjs with a 150k floor guarding degenerate SPOT states (empty models[],
absent contextWindow) - a zero budget would truncate every request to nothing.
CLAUDE_MAX_PROMPT_CHARS (env) and the runtime settings API remain ABSOLUTE overrides;
derivation applies only when neither is set. If models.json ever advertises a larger
window (e.g. 1M for the 1M-native models), the budget scales automatically - that
advertisement is a separate deliberate decision (quota burn, OpenClaw compaction, TUI
paste limits) explicitly NOT made here; see ADR 0009.
Behavior change (intended): requests between 150k and 600k chars previously truncated
now pass through whole - longer TTFT + higher quota use for those requests. Truncation
mechanism/logging unchanged; only the default's provenance changed.
ALIGNMENT.md Rule 2: no cli.js citation applies - the truncation guard is OCP-internal
prompt shaping; no endpoint, header, or wire field changes.
Tests: +4, doubly mutation-proven (max->min fails the largest-window test; dropping
the floor fails the floor test). Suite 347 passed / 0 failed. ADR 0009 + index row +
README env-table row included (release_kit: env var default change documented).
Co-Authored-By: Claude <claude-opus-4-8> <noreply@anthropic.com>
3.1 KiB
ADR 0009 — Prompt-char budget derives from the models.json SPOT
Date: 2026-07-18 Status: Accepted (maintainer directive, 2026-07-18: "37.5k 截断未免太短了吧 … 这个在现在还适用吗")
Context
MAX_PROMPT_CHARS (the tail-first truncation guard in messagesToPrompt) defaulted to a
hand-set constant of 150,000 chars ≈ 37.5k English tokens — set in the 200k-window era as a
runaway-context guard. Meanwhile models.json advertises contextWindow: 200000 for every
model (and the underlying CLI registry carries 1M native windows for Opus 4.8 / Sonnet 5), and
scripts/sync-openclaw.mjs feeds that 200k into OpenClaw's compaction budget. The result was
a standing dishonesty identified in the PR #152 review: no advertised contextWindow value was
true, because the proxy silently guillotined every request at ~37.5k tokens — roughly 5×
below the advertised window — logging only a server-side warning the client never sees.
Raising the constant to another hand-set number would rot the same way. Following the model's native 1M directly is also wrong: chars ≠ tokens (CJK runs ~1–1.5 chars/token vs ~4 for English, so a 1M-token char cap would let CJK text sail past the model's real window into an upstream rejection), single near-window requests can consume a large fraction of a 5-hour subscription quota window, and the TUI paste path is untested at megabyte scale.
Decision
The default budget derives from the SPOT instead of being a constant:
MAX_PROMPT_CHARS (default) = max(models.json models[].contextWindow) × 3 chars/token
= 200000 × 3 = 600,000 chars today
Implemented as the pure derivePromptCharBudget(models, {charsPerToken = 3, floor = 150000})
in lib/prompt.mjs (unit-tested; floor guards degenerate SPOT states). The multiplier ×3 is
deliberately conservative: full window for English, and CJK text reaches the model's real
window at roughly the same point the cap fires — so OCP truncates gracefully (tail-first)
instead of the upstream rejecting outright.
CLAUDE_MAX_PROMPT_CHARS (env) and the runtime settings API remain absolute overrides;
the derivation applies only when neither is set.
Consequences
- The advertised
contextWindow: 200000becomes honest: the proxy now actually accepts prompts of that order (English ≈150–200k tokens) before truncating. - If
models.jsonever advertises a larger window (e.g. 1M for the 1M-native models), the budget scales automatically — no code change. Whether to advertise 1M is a separate, deliberate decision (quota burn per request, OpenClaw compaction memory, TUI paste limits) and is explicitly NOT made by this ADR; the current recommendation is to keep 200000 advertised until a real >200k use case appears. - One-time behavior change: requests between 150k and 600k chars that were previously truncated now pass through whole — longer TTFT and higher quota consumption for those requests, by design.
- The truncation mechanism, logging, and the multimodal-path budget threading (PR #154's F2, pending) are unchanged — only the default value's provenance changed.