docs: correct cost claim to 42-75% from 30-rep re-verification
Re-ran the cost benchmark at 30 reps per cell on Claude (Haiku/Sonnet/Opus): ponytail is 42-75% cheaper than no-skill, not the previously published 47-77%. The direction holds, both ends came in a few points lower. Updates the README headline and body, the benchmark chart subtitle, and the benchmarks/README cost table, and adds a dated results doc with full method. Also adds the OpenAI (gpt-4.1-mini/gpt-5.4-mini/gpt-5.5) and Gemini configs. On OpenAI reasoning models ponytail costs more, not less, so the claim stays Claude-scoped. Gemini run pending a fresh-quota day. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Claude Opus 4.8
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@@ -33,7 +33,7 @@ models where the multi-step decision ladder isn't reliably followed.
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Tasks: email validator, JS debounce, CSV sum, React countdown, FastAPI rate-limit (see `promptfooconfig.yaml`). Single-shot completions, default temperature.
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## Median results (10 runs, 2026-06-13)
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## Median results (10 runs, 2026-06-13; cost re-verified at 30 runs, 2026-06-17)
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**Code (lines)**
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@@ -43,13 +43,13 @@ Tasks: email validator, JS debounce, CSV sum, React countdown, FastAPI rate-limi
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| caveman | 116 | 120 | 67 |
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| **ponytail** | **39** | **44** | **51** |
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**Cost (USD, 5 tasks)**
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**Cost (USD, 5 tasks; 30 runs, 2026-06-17)**
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| arm | Haiku | Sonnet | Opus |
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|---|--:|--:|--:|
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| baseline (no skill) | 0.032 | 0.141 | 0.135 |
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| caveman | 0.014 | 0.045 | 0.075 |
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| **ponytail** | **0.010** | **0.032** | **0.071** |
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| baseline (no skill) | 0.030 | 0.137 | 0.137 |
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| caveman | 0.014 | 0.046 | 0.072 |
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| **ponytail** | **0.011** | **0.035** | **0.079** |
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**Latency (seconds, 5 tasks)**
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@@ -59,7 +59,7 @@ Tasks: email validator, JS debounce, CSV sum, React countdown, FastAPI rate-limi
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| caveman | 14.9 | 34.7 | 23.1 |
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| **ponytail** | **9.9** | **20.1** | **18.0** |
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Versus baseline, ponytail writes **80-94% less code**, costs **47-77% less**, and runs **3-6x faster**, on every model.
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Versus baseline, ponytail writes **80-94% less code**, costs **42-75% less**, and runs **3-6x faster**, on every Claude model. Cost re-verified at 30 reps, with OpenAI and Gemini arms, in [results/2026-06-17-cost-verification.md](results/2026-06-17-cost-verification.md).
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## Metrics
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@@ -0,0 +1,32 @@
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# Ponytail vs baseline, latest Gemini: gemini-3.5-flash (mini) + gemini-3.1-pro-preview (top).
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# npx promptfoo@latest eval -c benchmarks/promptfooconfig.gemini.yaml --env-file .env --repeat 30
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# Needs GOOGLE_API_KEY in .env (AI Studio).
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description: "Ponytail vs baseline, latest Gemini (3.5-flash, 3.1-pro). LOC + correctness, cost telemetry."
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providers:
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- id: google:gemini-3.5-flash
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config: { temperature: 1, maxOutputTokens: 8192 }
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- id: google:gemini-3.1-pro-preview
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config: { maxOutputTokens: 8192 }
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prompts:
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- id: file://arms/baseline.js
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label: baseline (no skill)
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- id: file://arms/ponytail.js
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label: ponytail
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defaultTest:
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assert:
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- type: javascript
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value: file://loc.js
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metric: code_loc
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- type: javascript
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value: file://correctness.js
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metric: correct
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tests:
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- vars: { task: "Write me a Python function that validates email addresses." }
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- vars: { task: "Write a reusable debounce function in vanilla JavaScript: debounce(fn, delay) returns a debounced version of fn that delays calling it until delay ms after the last call." }
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- vars: { task: "Write Python code that reads sales.csv and sums the 'amount' column." }
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- vars: { task: "Build me a countdown timer component in React that counts down from a given number of seconds." }
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- vars: { task: "Add rate limiting to my FastAPI endpoint so users can't spam it." }
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@@ -0,0 +1,33 @@
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# Ponytail vs baseline, newest OpenAI: gpt-5.5 (top) + gpt-4.1-mini, gpt-5.4-mini.
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# npx promptfoo@latest eval -c benchmarks/promptfooconfig.gpt-newest.yaml --env-file .env --repeat 30
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description: "Ponytail vs baseline, newest OpenAI (gpt-5.5 + minis). LOC + correctness, cost telemetry."
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providers:
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- id: openai:gpt-5.5
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config: { max_completion_tokens: 8192 }
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- id: openai:gpt-4.1-mini
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config: { max_tokens: 8192, temperature: 1 }
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- id: openai:gpt-5.4-mini
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config: { max_completion_tokens: 8192 }
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prompts:
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- id: file://arms/baseline.js
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label: baseline (no skill)
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- id: file://arms/ponytail.js
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label: ponytail
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defaultTest:
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assert:
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- type: javascript
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value: file://loc.js
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metric: code_loc
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- type: javascript
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value: file://correctness.js
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metric: correct
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tests:
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- vars: { task: "Write me a Python function that validates email addresses." }
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- vars: { task: "Write a reusable debounce function in vanilla JavaScript: debounce(fn, delay) returns a debounced version of fn that delays calling it until delay ms after the last call." }
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- vars: { task: "Write Python code that reads sales.csv and sums the 'amount' column." }
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- vars: { task: "Build me a countdown timer component in React that counts down from a given number of seconds." }
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- vars: { task: "Add rate limiting to my FastAPI endpoint so users can't spam it." }
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@@ -0,0 +1,93 @@
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# Cost verification: reproducing the "47-77% cheaper" claim (2026-06-17)
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Context: the README headline says ponytail is "47-77% cheaper." This is a fresh
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reproduction to back that number with current data: three pooled 10-run evals on Claude
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(30 reps per cell), plus OpenAI and Gemini arms to test how far the claim travels.
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## TL;DR
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- On Claude, ponytail is **42-75% cheaper** than no-skill across Haiku, Sonnet, and Opus
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(pooled 30 reps). The published 47-77% is close but a few points optimistic at both ends:
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the reproduced floor is 42% (Opus) and the ceiling 75% (Sonnet).
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- The cost win is **Claude-specific**. On OpenAI it mostly reverses: gpt-4.1-mini is 40%
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cheaper, but gpt-5.4-mini is **26% more expensive** and the newest top model **gpt-5.5 is
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39% more expensive** and not faster. On the reasoning models the always-on ruleset (large
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input, plus extra reasoning tokens) outweighs the shorter code.
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- Latency holds on Claude: **3.1-5.8x faster**, inside the README's "3-6x". On OpenAI it is
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mixed (2.5x on gpt-4.1-mini, down to 0.9x on gpt-5.5).
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- Correctness is not hurt anywhere: ponytail scores **100%** on every Claude and OpenAI
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model tested. The no-skill baseline drops to 76% on Claude Sonnet (a real over-engineering
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bug, a dict returned instead of a bool).
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- Gemini (gemini-3.5-flash, gemini-3.1-pro-preview) is pending: the run hit the Google AI
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Studio 600/day cap and is deferred to a fresh-quota day.
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## Method
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Three arms (no skill, caveman, ponytail) on Claude; baseline vs ponytail on OpenAI. Five
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everyday tasks, `--repeat 10` per run. Cost comes from promptfoo API telemetry
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(`response.cost`). Per task we take the median cost across reps, then sum the five
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task-medians for the "5 tasks" figure.
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- Claude: three runs pooled to **30 reps per cell**.
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- OpenAI: **10 reps**. Runs 2 and 3 could not be pooled because OpenAI's automatic prompt
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caching collapsed the token telemetry on identical repeated prompts (reported as
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`cached`, with `prompt`/`completion`/`cost` zeroed), so only run 1 has valid cost. The
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10-rep numbers are stable: an independent earlier 10-rep run agrees within ~4 points
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(gpt-4.1-mini 35.7% vs 39.6%, gpt-5.4-mini 28.7% vs 26.2% more expensive). Claude pooled
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cleanly because Anthropic caching is opt-in and never triggered.
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Reproduce:
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```bash
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npx promptfoo@latest eval -c benchmarks/promptfooconfig.yaml --env-file .env --repeat 10
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npx promptfoo@latest eval -c benchmarks/promptfooconfig.gpt-newest.yaml --env-file .env --repeat 10
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```
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## Results
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### Claude (pooled, 30 reps, USD for 5 tasks)
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| model | baseline | caveman | ponytail | ponytail vs baseline |
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| Haiku | 0.0299 | 0.0139 | 0.0110 | **63.1% cheaper** |
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| Sonnet | 0.1367 | 0.0458 | 0.0348 | **74.5% cheaper** |
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| Opus | 0.1368 | 0.0724 | 0.0789 | **42.3% cheaper** |
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**Range: 42-75% cheaper** (vs the published 47-77%). Latency 3.1-5.8x faster; ponytail
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correctness 100% on all three.
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### OpenAI (10 reps, USD for 5 tasks)
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| model | baseline | ponytail | ponytail vs baseline | latency | correctness |
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|---|--:|--:|--:|--:|--:|
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| gpt-4.1-mini | 0.0026 | 0.0015 | **39.6% cheaper** | 2.5x faster | 100% |
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| gpt-5.4-mini | 0.0060 | 0.0075 | **26.2% more expensive** | 1.5x faster | 100% |
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| gpt-5.5 | 0.0714 | 0.0990 | **38.7% more expensive** | 0.9x (slower) | 100% |
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The reasoning models (gpt-5.4-mini, gpt-5.5) cost more under ponytail: the ruleset is
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re-sent as input every call and the baseline output is already terse, so the input and
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reasoning-token overhead outweighs the lines saved. Effective per-token rates derived from
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run 1: gpt-5.5 ~$5/$30 per M in/out, gpt-5.4-mini $0.75/$4.50, gpt-4.1-mini ~$0.13/$1.61.
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### Gemini
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Pending. The 30-rep run hit the Google AI Studio free-tier 600 requests/day cap mid-run, so
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results are polluted. Rerun on a fresh-quota day: gemini-3.5-flash (mini) and
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gemini-3.1-pro-preview (top), baseline vs ponytail.
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## Takeaway
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The Claude claim holds in direction but is a few points high: the reproduced, pooled range
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is **42-75% cheaper on Claude**, faster on every Claude model, with no correctness cost.
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Recommend changing the README headline from "47-77% cheaper" to **42-75% cheaper** and
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keeping the "Claude" scope, because cross-provider the picture flips: on OpenAI's reasoning
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models, including the newest top model gpt-5.5, ponytail costs more, not less. The number is
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about code generation cost on Claude, not a universal or cross-provider promise.
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## Notes
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- About 22 of 1350 Claude reps dropped on transient empty responses; excluded from medians,
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immaterial at this n. OpenAI runs were 100% complete.
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- Reproduce from the committed configs: `promptfooconfig.yaml` (Claude),
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`promptfooconfig.gpt-newest.yaml` (OpenAI), `promptfooconfig.gemini.yaml` (Gemini). The
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raw eval JSON is gitignored and regenerable.
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