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feat(proxy): report new-content-relative input savings rate in /stats (#2058)
## Description The whole-request savings ratios in `/stats` (`proxy_savings_percent`, `savings_percent`) divide by a per-request recount of the full transcript: a session at turn 200 has had its history counted 200 times into the denominator. Long-running cached sessions — 1M-context models especially, since they never compact — therefore read as ~0% savings no matter how well compression performs on content that actually newly enters context. Field example that motivated this: one day of 1M-context Claude Code traffic saved 641K tokens against ~13.4M tokens of genuinely new content (~4.8%), but displayed as 0.14% because the summed full-transcript denominator was 475M. This PR adds a new-content-relative rate alongside the existing fields: - `tokens.new_input_tokens` — provider-billed non-cache-read input (uncached + cache-write tokens, summed from response usage across providers; the cache accumulators already track both). - `tokens.new_input_savings_percent` — `saved / (new_input + saved)`. Tokens Headroom removed never reached the provider, so they're added back to form the baseline: "of the input that would have newly entered context, what fraction did Headroom remove?" Purely additive — no existing field changes, no new accumulators. ## Type of Change - [ ] Bug fix (non-breaking change that fixes an issue) - [x] New feature (non-breaking change that adds functionality) - [ ] Breaking change (fix or feature that would cause existing functionality to change) - [ ] Documentation update - [ ] Performance improvement - [ ] Code refactoring (no functional changes) ## Changes Made - `headroom/proxy/server.py`: compute `new_input_tokens` from `prefix_cache_stats["totals"]` (already built for `/stats`) and emit the two new fields in the `tokens` block. Rate is guarded on `new_input_tokens > 0`: the cache accumulators only see requests with cache activity, so a deployment with no cache metrics (e.g. Bedrock) would otherwise divide savings by themselves and report ~100% — it reports 0 instead. - `tests/test_stats_new_input_savings_rate.py`: endpoint-level tests via `TestClient(create_app(...))` — a long-cached-session request shows 9.09% new-content rate while `proxy_savings_percent` stays diluted at 0.5%; and the no-cache-usage-data case reports 0. - `CHANGELOG.md`: Features entry. ## Testing - [x] Unit tests pass (`pytest`) - [x] Linting passes (`ruff check .`) - [x] Type checking passes (`mypy headroom`) - [x] New tests added for new functionality - [ ] Manual testing performed ### Test Output ```text $ uv run --frozen --extra dev pytest tests/test_stats_new_input_savings_rate.py -v tests/test_stats_new_input_savings_rate.py::test_stats_reports_new_input_savings_rate PASSED tests/test_stats_new_input_savings_rate.py::test_stats_new_input_rate_is_zero_without_cache_usage_data PASSED ========================= 2 passed, 1 warning in 6.78s ========================= $ uv run --frozen --extra dev pytest tests/test_proxy_savings_history.py tests/test_dashboard_token_savings.py tests/test_proxy_cache_ttl_metrics.py ======================== 57 passed, 1 warning in 10.70s ======================== $ uv run --frozen --extra dev mypy headroom/proxy/server.py Success: no issues found in 1 source file $ ruff check headroom/proxy/server.py tests/test_stats_new_input_savings_rate.py All checks passed! $ ruff format --check headroom/proxy/server.py tests/test_stats_new_input_savings_rate.py 2 files already formatted ``` ## Real Behavior Proof - Environment: macOS 15 (darwin 24.6.0), Python 3.10 via `uv run --frozen --extra dev`. - Exact command / steps: `TestClient(create_app(config))`, record a request shaped like a late turn of a long cached session (`input_tokens=1_000_000, tokens_saved=5_000, cache_read=900_000, cache_write=45_000, uncached=5_000`), then `GET /stats`. - Observed result: `tokens.new_input_tokens == 50_000`, `tokens.new_input_savings_percent == 9.09`, while `proxy_savings_percent` stays `0.5` — the dilution the new field exists to correct, reproduced side by side. - Not tested: not run against a live proxy with real provider traffic; `ruff`/`mypy` run scoped to the changed files rather than the whole repo. ## Review Readiness - [x] I have performed a self-review - [x] This PR is ready for human review ## Checklist - [x] My code follows the project's style guidelines - [x] I have performed a self-review of my code - [x] I have commented my code, particularly in hard-to-understand areas - [x] I have made corresponding changes to the documentation - [x] My changes generate no new warnings - [x] I have added tests that prove my fix is effective or that my feature works - [x] New and existing unit tests pass locally with my changes - [x] I have updated the CHANGELOG.md if applicable ## Screenshots (if applicable) N/A — JSON API addition; dashboard adoption can follow separately. ## Additional Notes - No linked issue; companion to the nested tool_result image token-counting fix (same investigation — that PR fixes the inflated numerator/denominator counts, this one fixes the metric that divides by transcript recounts). - Caveat worth a reviewer's eye: the numerator (`tokens_saved_total`, local tokenizer) and denominator (provider-reported usage) come from different counters. They're on the same scale, but the rate is honest-approximate rather than exact — comment in code says so. - Deliberately did not change the dashboard headline or any existing field semantics; consumers can opt into the new rate. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: Claude Fable 5 <noreply@anthropic.com> Co-authored-by: JerrettDavis <mxjerrett@gmail.com>
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@ -81,6 +81,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
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### Features
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* **proxy:** report a new-content-relative input savings rate in `/stats`: `tokens.new_input_tokens` (provider-billed non-cache-read input: uncached + cache-write tokens, from response usage) and `tokens.new_input_savings_percent` (savings as a fraction of new input plus the tokens compression removed before they could be billed). The existing whole-request ratios recount the full transcript on every turn, so a 200-turn session counts its history 200x into the denominator and long-running cached sessions (especially 1M-context models, which never compact) dilute toward ~0% regardless of how well compression performs on content newly entering context. Purely additive; existing fields unchanged. Reports 0 when no cache usage data exists (e.g. providers without cache metrics) rather than dividing savings by themselves.
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* **transforms:** first-class C# support in `CodeAwareCompressor` via the tree-sitter `csharp` grammar already shipped in the pinned `tree-sitter-language-pack` — no new dependencies ([#1664](https://github.com/headroomlabs-ai/headroom/issues/1664)). Parity with Java/C++/Rust: signatures preserved verbatim, method/constructor/destructor/operator/local-function bodies compressed; block-scoped and file-scoped namespaces, records, structs, interfaces, and enums handled; C#-distinctive auto-detection. Preprocessor conditionals (`#if`…`#endif`) are preserved verbatim as opaque regions (blocks wrapping only `using` directives stay with the imports), `#region` markers no longer swallow the following line during class-member extraction, and top-of-file license banners / `#region License` headers stay on top instead of being relocated below the code. Real-repo runs: 16.1% tokens saved on Newtonsoft.Json (945 files), 37.8% on Polly (797 files), output syntax-valid for 1742/1742 files.
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* **proxy:** add provider-only HTTP proxy routing via `--http-proxy` and `HEADROOM_HTTP_PROXY`. Upstream LLM provider calls can now use an HTTP proxy without setting process-wide `HTTP_PROXY`/`HTTPS_PROXY` variables that are inherited by tool executions; proxied provider clients use HTTP/1.1 so HTTPS provider APIs can tunnel through CONNECT.
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* **proxy:** add output shaping for OpenAI Responses traffic on `/v1/responses` HTTP requests and Codex WebSocket `response.create` frames, with stable output-savings holdout keys and counted WS token strata for the experiment.
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@ -3112,6 +3112,19 @@ def create_app(config: ProxyConfig | None = None) -> FastAPI:
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# schema size. So the savings rate is plain `saved / attempted`
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# — adding `saved` again would double-count.
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attempted_input_tokens = getattr(m, "attempted_input_tokens_total", 0)
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# New-content denominator: what the provider actually billed as
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# non-cache-read input (uncached + cache-write tokens, summed
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# across providers from response usage). Unlike
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# `proxy_total_before_compression`, this does NOT recount the
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# full transcript on every turn — a long session's history is
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# served from prefix cache, not re-billed, so it doesn't belong
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# in a denominator that claims to measure what compression had
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# any power over. Tokens Headroom removed never reached the
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# provider at all, so they're added back to form the baseline.
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_pc_totals = prefix_cache_stats.get("totals", {})
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new_input_tokens = int(_pc_totals.get("uncached_input_tokens", 0) or 0) + int(
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_pc_totals.get("cache_write_tokens", 0) or 0
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)
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# Build human-readable summary
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summary = _build_session_summary(
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@ -3340,6 +3353,27 @@ def create_app(config: ProxyConfig | None = None) -> FastAPI:
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else 0,
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2,
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),
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# New-content-relative rate: savings as a fraction of the
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# input that would have newly entered context (provider-
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# billed uncached + cache-write tokens, plus the tokens
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# compression removed before they could be billed). The
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# whole-request ratios above recount the FULL transcript
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# every turn, so a 200-turn session counts its history
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# 200x into the denominator and long-running sessions
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# (1M-context models never compact) read as ~0% no
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# matter how well compression performs on new content.
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# Guarded on new_input_tokens > 0 (not the full sum): the
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# cache accumulators only see requests with cache
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# activity, so a deployment with no cache metrics (e.g.
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# Bedrock) would otherwise divide savings by themselves
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# and report ~100%. No usage data -> report 0, not a lie.
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"new_input_tokens": new_input_tokens,
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"new_input_savings_percent": round(
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(proxy_compression_tokens / (new_input_tokens + proxy_compression_tokens) * 100)
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if new_input_tokens > 0
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else 0,
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2,
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),
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"savings_percent": round(
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(all_layers_tokens_saved / total_tokens_before * 100)
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if total_tokens_before > 0
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81
tests/test_stats_new_input_savings_rate.py
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81
tests/test_stats_new_input_savings_rate.py
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@ -0,0 +1,81 @@
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"""New-content-relative savings rate in /stats (tokens.new_input_savings_percent).
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The whole-request ratios recount the full transcript on every turn, so long
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cached sessions dilute toward 0% regardless of how well compression performs
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on content that newly enters context. The new rate divides by provider-billed
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non-cache-read input (uncached + cache-write) plus the tokens compression
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removed before they could be billed.
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"""
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from __future__ import annotations
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import asyncio
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from fastapi.testclient import TestClient
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from headroom.proxy.server import ProxyConfig, create_app
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def _make_client(tmp_path, monkeypatch) -> TestClient:
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monkeypatch.setenv("HEADROOM_SAVINGS_PATH", str(tmp_path / "proxy_savings.json"))
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config = ProxyConfig(
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cache_enabled=False,
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rate_limit_enabled=False,
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log_requests=False,
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)
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return TestClient(create_app(config))
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def test_stats_reports_new_input_savings_rate(tmp_path, monkeypatch):
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with _make_client(tmp_path, monkeypatch) as client:
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proxy = client.app.state.proxy
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# A late turn of a long cached session: the local transcript recount
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# (input_tokens) dwarfs what the provider newly billed (uncached +
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# cache_write = 50k), so the whole-request ratio dilutes to ~0.5%
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# while the new-content rate reports the undiluted 9.09%.
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asyncio.run(
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proxy.metrics.record_request(
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provider="anthropic",
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model="claude-opus-4-6",
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input_tokens=1_000_000,
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output_tokens=200,
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tokens_saved=5_000,
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latency_ms=10.0,
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cache_read_tokens=900_000,
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cache_write_tokens=45_000,
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uncached_input_tokens=5_000,
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)
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)
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stats = client.get("/stats")
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assert stats.status_code == 200
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tokens = stats.json()["tokens"]
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assert tokens["new_input_tokens"] == 50_000
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# 5_000 saved / (50_000 billed-new + 5_000 saved) = 9.09%
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assert tokens["new_input_savings_percent"] == 9.09
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# The transcript-diluted ratio stays as-is — the new rate sits alongside,
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# it does not replace existing fields.
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assert tokens["proxy_savings_percent"] == 0.5
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def test_stats_new_input_rate_is_zero_without_cache_usage_data(tmp_path, monkeypatch):
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with _make_client(tmp_path, monkeypatch) as client:
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proxy = client.app.state.proxy
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# Savings recorded but no cache usage observed (provider without
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# cache metrics): the rate must report 0, not savings/savings=100%.
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asyncio.run(
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proxy.metrics.record_request(
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provider="bedrock",
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model="claude-opus-4-6",
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input_tokens=10_000,
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output_tokens=200,
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tokens_saved=2_000,
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latency_ms=10.0,
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)
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)
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tokens = client.get("/stats").json()["tokens"]
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assert tokens["new_input_tokens"] == 0
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assert tokens["new_input_savings_percent"] == 0
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