# pxpipe

**Cut Claude Code's input tokens by rendering bulky context as images — the same system prompt, tool docs, and history, in a fraction of the tokens.**

An image's token cost is fixed by its pixel dimensions, not by how much text
is inside it. Dense content (code, JSON, tool output) packs ~3.1 chars per
image-token vs ~1 char per text-token on real Claude Code traffic. The
reader is the same vision channel that Anthropic's computer use already
relies on for screenshots. pxpipe is a local proxy that uses that channel
for context: it rewrites the bulky parts of each request into compact PNGs
before it leaves your machine. At current Fable
list prices that lands as a **~59–70% lower end-to-end bill** — but prices
move and workloads differ, so the durable number is the token cut itself,
measured per-request against a free `count_tokens` counterfactual in
`~/.pxpipe/events.jsonl`.

This is what the model sees instead of text:

![example: a real `transformRequest` output: system prompt + tool docs reflowed into one dense page, instruction banner on top, ↵ marking original newlines](https://raw.githubusercontent.com/teamchong/pxpipe/main/docs/assets/example-render.png)

*~48k chars of system prompt + tool docs: ≈25k tokens as text, ≈2.7k image
tokens as this page. Real pipeline output; the model reads renders like this
at 100/100 (see benchmarks).*

![chart: characters a frontier context window holds, 2018–2026 — vendor text series including Grok 4.5; orange measured overlay is Fable 5 [1m] + pxpipe ~18M (4.6×)](docs/assets/context-window-chars.png)

*Eight years of context growth, in characters. Every text line tops out near
~4M chars (a 1M-token window at ~4 chars/token); **Grok 4.5** is shown as a
text-window point only (500K). The orange overlay is the **same Fable 5 1M
window** read through pxpipe images — ~18M chars at the measured Anthropic
density (**4.6×** the text ceiling). Density is measured from a live render at
generation time, not hand-typed: regenerate with
`npx tsx scripts/gen-context-chart.ts`
([source](scripts/gen-context-chart.ts)).*

## Demo

**Fable 5 (the default, 100/100 reader) — plain left, pxpipe right:**

https://github.com/user-attachments/assets/1c8ee63a-fcd7-4958-917b-da788d718349

pxpipe counts an exact token **10/10** across 39 imaged filler files
(matches `grep` line-for-line), gets the multi-step ledger arithmetic right,
and ends the session at **$6.06** with context to spare (73.5k/1M) vs
**$42.21** at 96% full. One caveat visible in the clip: the pxpipe arm
needed a nudge to match the requested one-line output format.

**Opus 4.8 (disabled by default) — same layout:**

https://github.com/user-attachments/assets/f4e50137-31b5-426f-a6ed-b83f829b4a2c

Text needles read fine on both arms; the imaged phrase-count doesn't read on
Opus — and pxpipe **says so instead of fabricating a number**. That misread
rate is why Opus is opt-in.

## Try it (30 seconds)

```bash
npx pxpipe-proxy                                  # proxy on 127.0.0.1:47821
ANTHROPIC_BASE_URL=http://127.0.0.1:47821 claude  # point Claude Code at it
```

Dashboard at <http://127.0.0.1:47821/>: tokens saved, every text→image
conversion side by side, kill switch, live model chips. Responses stream
normally — pxpipe compresses the *request* only, never the model's output.
Recent turns stay text; the system prompt, tool docs, and older bulk history
are imaged.

## The honest part

- **It is lossy.** Exact 12-char hex strings in dense imaged content:
  **13/15** on Fable 5, **0/15** on Opus, and **0/15** on Sol — misses are *silent
  confabulations*, not errors. Byte-exact values (IDs, hashes, secrets)
  must stay text; recent turns do. A dedicated verbatim-risk guard is not
  built yet.
- **Escape hatch:** subagents on non-allowlisted models pass through as
  text — route byte-exact work there
  (`CLAUDE_CODE_SUBAGENT_MODEL=claude-sonnet-4-6`, or `model: sonnet` in
  agent frontmatter).
- **Real work:** SWE-bench Lite pilot **10/10 both arms** at −65% request
  size; SWE-bench Pro **14/19 ON vs 15/19 OFF** at −60%, verdicts agree
  18/19, and the single split re-resolved 3/3 on replication — run-to-run
  variance, not compression. Small n; receipts in `eval/`.
- **Workload-dependent.** Wins on token-dense content (~1 char/token),
  loses money on sparse prose (~3.5 chars/token); a profitability gate
  (calibrated on N=391 production rows) images only where the math wins.
- **Client-dependent, not product-name-dependent.** Savings track uncached
  bulk the client still re-sends as text. Claude Code re-sends system + tools
  + history on `/anthropic/messages` and typically lands ~60–70%. Codex on
  `/v1/responses` is supported; when the prompt is already ~98%
  `cached_tokens`, only the static slab (and rare history collapses) remain
  to image, so Saved can honestly sit near 1%. The same Responses path saves
  tens of percent when history collapse fires, and an OpenAI client that
  re-sends the full transcript as plain text each turn is in the same high-
  savings class as Claude Code. Details and measured splits:
  [docs/CACHING_AND_SAVINGS.md](docs/CACHING_AND_SAVINGS.md#openai-responses-path-codex-and-friends).
- **Model scope:** default `PXPIPE_MODELS=claude-fable-5`. Sol, Opus
  4.7/4.8, GPT 5.5, and **Grok** are opt-in only (dashboard chips or
  `PXPIPE_MODELS`) — not good enough as silent defaults for imaged context.
  Grok packing + factsheet helps exact IDs, but quality remains below Fable:
  82/100 arithmetic, 83/98 gist, and 13/18 state tracking. The exact Sol id
  still matters. Sibling variants such as `gpt-5.6-terra` do not
  inherit Sol's allowlist or render profile. `PXPIPE_MODELS=off` disables
  imaging. Everything else passes through byte-identical. On the GPT path,
  tool definitions stay native JSON and no Anthropic `cache_control`
  markers are used. Responses history compression recognizes adjacent completed
  `function_call`/`function_call_output` pairs: only old closed pairs are imaged;
  the newest six completed pairs, every open call, and malformed/orphan state
  remain native. The default history budget is 32 images; opt-in long-session
  coverage can be raised (defensive cap 100) with
  `PXPIPE_GPT_HISTORY_MAX_IMAGES=48` after validating the provider's request cap.
- **Per-model rendering:** opt-in `gpt-5.6-sol` uses a 152-column,
  5×8 Spleen profile; Claude keeps its 312-column 5×8 Spleen profile. These
  are selected by exact model id, including history pages and profitability
  math. **Sol quality:** production 5×8 scored 98/100 arithmetic and 79/93
  completed gist, 18/18 state, 4/15 completed never-stated confabulations,
  and 0/15 dense hex. Exact IDs therefore use the verbatim factsheet, and recent/open tool state stays native.
  [Sol receipts](eval/sol-profile/QUALITY_RESULTS.md) and
  [profile evidence](docs/MODEL_RENDER_PROFILES.md).
- **Grok 4.5 (opt-in):** same production recipe as Sol (5×8 Spleen, IDS, text
  factsheet; Grok strip maxH 512). Off by default (not Fable-level pure-image).
  Measured production results are 82/100 arithmetic, 83/98 gist, and 13/18
  state tracking. Enable with
  `PXPIPE_MODELS=claude-fable-5,grok-4.5` or the dashboard chip.
  [eval/grok-density/QUALITY_RESULTS.md](eval/grok-density/QUALITY_RESULTS.md).

## Benchmarks (reproducible)

### Model quality (does the model read the images?)

Every model row below uses the same production recipe unless a pure-image
research arm is called out: **5×8 Spleen + IDS block + adjacent text factsheet**.
Claude numbers are novel problems the model cannot have memorized. Sol and Grok
quality use Codex’s Responses provider; Fable/Opus use Claude. Token deltas
compare matched input arms: negative saves tokens; positive costs more. The
historical GSM8K run measured −38%, but it is a different corpus and is not
used for these novel-arithmetic rows.

| test | model | N | text | pxpipe (image) | tokens |
|---|---|---:|---:|---:|---|
| novel arithmetic | `claude-fable-5` | 100 | 100% | **100%** | not measured |
| novel arithmetic | `gpt-5.6-sol` | 100 | 100% | **98%** | **+32%** |
| novel arithmetic | `claude-opus-4-8` | 100 | 100% | 93% | not measured |
| novel arithmetic | `grok-4.5` | 100 | 100% | **82%** | **+7%** |
| gist recall A/B (decisions, values, paths, names, negations; distractors; 15k–45k char sessions) | Fable 5 | 98/arm | 98/98 | **98/98** | not measured |
| same gist corpus, production images + factsheet | `gpt-5.6-sol` | 98 | not measured | **79/93 completed; 1 session error** | not measured |
| same gist corpus, production images + factsheet | `grok-4.5` | 98 | 98/98 | **83/98** | not measured |
| state tracking (value mutated 3×, final/first/count) | Fable 5 | 18/arm | 18/18 | **18/18** | not measured |
| same state-tracking corpus | `gpt-5.6-sol` | 18 | not measured | **18/18 latest** | not measured |
| same state-tracking corpus | `grok-4.5` | 18 | 18/18 | **13/18** | not measured |
| confabulation on never-stated facts (lower is better) | Fable 5 | 16/arm | 0/16 | **0/16** | not measured |
| same never-stated probes (lower is better) | `gpt-5.6-sol` | 16 | not measured | **4/15 completed; 1 session error** | not measured |
| same never-stated probes (lower is better) | `grok-4.5` | 16 | 0/16 | **0/16** | not measured |
| verbatim 12-char hex, dense render | Opus | 15 | 15/15 | **0/15** | not measured |
| verbatim 12-char hex, dense render | Fable 5 | 15 | not measured | **13/15** | not measured |
| verbatim 12-char hex, same dense pages | `gpt-5.6-sol` | 15 | not measured | **0/15** | not measured |
| verbatim 12-char hex, same dense pages | `grok-4.5` | 15 | 15/15 | **0/6 completed; 9 transport errors** | not measured |

**Harness split:** Fable/Opus quality and SWE-bench rows use **Claude**; Sol and Grok quality use
**Codex’s Responses provider** (`OPENAI_BASE_URL`, typically ocproxy) — see
[`eval/grok-density/QUALITY_SUITE.md`](eval/grok-density/QUALITY_SUITE.md).

Sol receipts: [`eval/sol-profile/QUALITY_RESULTS.md`](eval/sol-profile/QUALITY_RESULTS.md).
Grok receipts: [`eval/grok-density/QUALITY_RESULTS.md`](eval/grok-density/QUALITY_RESULTS.md).
SWE-bench is not copied to Sol: its runner is Claude Code/Fable-specific
(`ANTHROPIC_BASE_URL`, Claude CLI, official Docker grading), and no Sol ON/OFF
run exists yet. Pure-image-only is **not** Fable-grade on live Grok.

### Capacity / density (how many chars per vision-token?)

Measured by rendering this repo’s dense fixture through the real pipeline and
pricing pixels at each family’s vision rate. Multiplier = measured
chars/vision-token ÷ 4 (prose text baseline). Not a model-quality score.

| family | window | as text (@4 c/tok) | as pxpipe images | density | multiplier |
|---|---:|---:|---:|---:|---:|
| **`claude-fable-5[1m]`** (default) | 1M | ~4.0M | **~18.3M** | ~18.3 c/vt (px÷750) | **~4.6×** |

Regenerate: `npx tsx scripts/gen-context-chart.ts` · chart PNG
[`docs/assets/context-window-chars.png`](docs/assets/context-window-chars.png).

SWE-bench run totals, receipts, and caveats:
[`eval/swe-bench/`](eval/swe-bench/) ·
[`eval/swe-bench-pro/`](eval/swe-bench-pro/) ·
[`eval/needle-haystack/`](eval/needle-haystack/) ·
[`eval/gist-recall/`](eval/gist-recall/) ·
[`eval/grok-density/`](eval/grok-density/) · analysis in
[`FINDINGS.md`](FINDINGS.md). (GSM8K scored 96% imaged, but it's in training
data — memorized answers survive misreads — so we lead with the novel-number
evals.)

## How it works

```
model id ──► render profile ──► wrap/reflow bulk context ──► PNG[] + exact-token factsheet
```

The proxy intercepts `/v1/messages`, rewrites eligible bulk into image
blocks, splices them back cache-friendly (static prefix preserved, prompt
caching keeps working), and forwards. Every enabled model gets the same
production stack: 5×8 Spleen pages, in-image IDS block, and adjacent text
factsheet. Claude uses 1568×728 pages; GPT 5.6 Sol uses 768px-wide portrait
strips; opt-in Grok 4.5 uses 152-col strips (maxH 512). A
per-request estimator uses that same resolved profile, so sparse prose stays
text. Events log to `~/.pxpipe/events.jsonl`.

## Library use (no proxy)

```ts
import { renderTextToImages, transformAnthropicMessages } from "pxpipe-proxy";

const { pages } = await renderTextToImages(toolResultText);     // pages[i].png: Uint8Array
const { body, applied, info } = await transformAnthropicMessages({
  body: requestBytes,
  model: "claude-fable-5",
});
```

`options.keepSharp(block)` pins blocks as text; `options.emitRecoverable`
returns the originals of imaged blocks. Pure-JS runtime (Node and
edge/Workers); `@napi-rs/canvas` is build-time only. Full API:
`src/core/index.ts`.

## Development

```bash
pnpm install && pnpm test
pnpm run build                # regenerates dist/
```

## FAQ

**Is the headline end-to-end, or only on the requests you touched?**
End-to-end, the whole bill. Most compression tools report savings only on
the input slice they touched, which flatters the number. The end-to-end
denominator is *every* production request: the small ones pxpipe correctly
left untouched, all cache writes and reads, and all output tokens (which the
proxy never compresses). On a 13,709-request snapshot that was 59% ($100 →
~$41); a later 8,904-compressed-request trace measured ~70%. Compressed-only
runs higher (~72–74%) and is quoted separately, never as the headline. The
exact figure is workload-dependent — reproduce it on your own log.

**How is the math measured?**
Both sides of the same request, at the same moment. For every `/v1/messages`
POST the proxy fires a free `count_tokens` probe on the original uncompressed
body (the counterfactual) in parallel with the real forward, and reads
Anthropic's actually-billed usage block off the response. Both land in the
same row of `~/.pxpipe/events.jsonl`, so there is no turn-count or
run-to-run confound. Dollar conversion uses Fable 5 list ratios: input ×1.0,
cache write ×1.25, cache read ×0.1, output ×5. Cache pricing is applied
identically to both sides, so the caching discount cancels and cannot be
double-counted as "savings". Re-derive it yourself from the events log: the
formula and field names are documented in `src/core/baseline.ts`.

**What does it actually compress?**
Three kinds of *input* blocks, each behind a profitability gate:

1. large `tool_result` bodies (file reads, command output, logs) above
   ~6k chars of token-dense content
2. older collapsed history: turns behind the live tail get re-rendered as
   image pages, recent turns always stay text
3. the static system prompt + tool docs slab

Everything else passes through byte-identical: your messages, recent turns,
the model's output (it is the response, the proxy never touches it), sparse
prose, and anything too small to win. Fable 5 is the only built-in default. Sol,
Opus, GPT 5.5, and Grok remain explicit opt-ins. Sol's production 5×8 run
scored 98/100 arithmetic, 79/93 completed gist, 18/18 state, 4/15 completed
never-stated confabulations, and 0/15 dense hex. Grok scored 82/100
arithmetic, 83/98 gist, and 13/18 state.

**Has it ever failed for real, outside the benchmarks?**
Yes, once in weeks of daily use: the model recalled a person's name from
imaged chat history and got it confidently wrong. No error, just a
plausible wrong name. That is the documented failure mode: exact strings
in imaged content are not byte-safe. Coding sessions tolerate this because
the agent re-reads files before editing; pure chat recall has no such check.
This failure mode is measured, not anecdotal:
[the legibility audit](docs/LEGIBILITY-AUDIT-2026-07-01.md) quantifies
exact-string recall off rendered pages (blind reads top out at 63% on dense
identifiers, with every miss predicted by a glyph-confusability matrix) and
documents the shipped mitigations — page geometry clamped to the API's
resample cap so billed pixels actually reach the vision encoder, and exact
identifiers (SHAs, numbers) riding alongside as text.

**Why are misses silent confabulations instead of read errors?**
Because model vision is not OCR: the image becomes patch embeddings, never
discrete characters, so there is no per-glyph confidence to fail loudly
on. When pixels underdetermine a glyph, the language prior fills the gap
with something plausible. Mechanism and receipts:
[docs/NOT-OCR.md](docs/NOT-OCR.md).

**Didn't DeepSeek-OCR show this doesn't hold up in practice?**
No: it proved the channel works, using an encoder/decoder pair trained for
the job. The skepticism dates from October 2025, when no stock production
model could read dense renders; that changed with Fable 5 (0/15 verbatim
hex on Opus 4.8 vs 13/15 on Fable 5, same pages). Timeline and per-model
numbers: [docs/NOT-OCR.md](docs/NOT-OCR.md).

**Why does the README read like an AI wrote it?**
Because one did. Most of this repo's commits — the code and the docs — were
authored by Opus/Fable agent sessions running behind pxpipe itself, reading
their own collapsed history as image pages while they worked.

## Limitations

- Lossy (above); verbatim recall from images is unreliable.
- PNG encoding adds latency to large requests before they leave.
- ASCII/Latin-1 well tested; CJK works but conservatively.

## Roadmap

Rendering research is parked as of 2026-07-05: verbatim misreads are
capacity-bound, not trick-bound, so no font/color/layout change fixes
exact-string recall at profitable density. The why is in
[docs/NOT-OCR.md](docs/NOT-OCR.md); the dated analysis and the three
documented follow-up threads (glyph-style A/B with banked pages, runtime
canary + re-fetch, surrogate-reader pre-flight) are in
[FINDINGS.md](FINDINGS.md), 2026-07-05 entry. Watch condition: re-run the
resolution sweep per model release; readable density moved ~4x in glyph
area from Opus 4.8 to Fable 5, and a model that reads production cells
near 100% means savings rise for free.

Still open, unchanged: whether imaged bulk stretches effective context (~2x
the real content in the same 1M window), and whether a smaller active
context improves long-task accuracy. Hypotheses, not claims — they ship as
numbers with an n or they get cut.

## License

MIT.