cost-cliff

Would the cheap model really have been cheaper? cost-cliff replays your own Claude Code and Codex sessions against other models' price tables. It includes the prompt-length tiers that list prices hide: the Haiku 5.5 line at 100K tokens and the GPT-6 line at 272K.

Also a Claude Code skill. cost-cliff is part of agent-preflight, 16 offline checks for coding agents: /plugin marketplace add thinx-pro/agent-preflight then /plugin install cost-cliff@agent-preflight, and ask Claude in plain words.

_{The screenshot shows the bundled synthetic demo: three agent sessions whose context grows a few K tokens per turn and gets compacted. Run cost-cliff on your own logs to get your own numbers.}

Why

Claude Haiku 5.5 costs $0.10 / $0.50 per million tokens, but only for prompts up to 100,000 tokens. A longer prompt is billed entirely at $0.50 / $2.50, five times as much (Anthropic pricing). GPT-6 Luna and Sol do the same thing above 272K (OpenAI pricing). Agent sessions resend their whole context every turn, so a long session spends most of its turns over 100K.

When Haiku 5.5 launched, a widely discussed r/ClaudeAI comparison found the same task cost 12.7× more on Haiku 5.5 than on GPT-6 Luna, The prompt wasn't published, but commenters agreed the 100K tier was the main reason. You can't tell from a price page which model is cheaper for your work. Your logs can tell you, because they record every request's prompt size and cache split.

Quick start

npx github:thinx-pro/cost-cliff

This reads ~/.claude/projects and ~/.codex/sessions for the last 30 days and prints a report. Nothing leaves your machine.

npx github:thinx-pro/cost-cliff --since all --html report.html   # all history + HTML report

What you get

cost-cliff 0.1.0  470 requests · 3 sessions · 2026-10-01 → 2026-10-01
sources: Claude Code 470 · prices as of 2026-10-08

Prompt size per request   p50 108K · p90 175K · max 215K
  0–50K      █████                               44    9%
  50–100K    ████████████████████               167   36%
  100–200K   ██████████████████████████████     248   53%
  200–272K   █                                   11    2%
  272K–500K                                       0    0%
  500K+                                           0    0%

Same trajectory, replayed on
  model          est. cost   requests over cliff   cliff premium
  Opus 5.5          $35.95   no tier               —
  Sonnet 5.5        $17.97   no tier               —
  Haiku 5.5          $4.04   259 (55%) >100K       $2.89 (72% of bill)
  GPT-6 Sol         $19.87   0 >272K               —
  GPT-6 Luna        $0.993   0 >272K               —

Actual list-price cost of what ran: $17.97 over 470 requests
→ Haiku 5.5: 55% of your requests are over its 100K line, and that is 72% of its bill.

(This output is from the synthetic demo in demo/. To reproduce it, clone the repo and run node bin/cost-cliff.js demo --since all. scripts/make-demo.js regenerates the demo sessions.)

• Prompt-size histogram of every request, colored by which tier lines it crosses.
• Replay table: the same requests priced on each model, how many cross that model's tier line, and the cliff premium, meaning the extra you'd pay because those requests went over the line.
• Actual cost of what ran, at list price for the model that actually served each request. This includes Opus fast mode and the 1.1× US-only inference multiplier when the log records them.
• --json for scripts and --html for a self-contained report you can share.

Options

--since <30d|12h|YYYY-MM-DD|all>  time window (default: 30d)
--source <claude|codex|all>       which default log dirs to read
--project <text>                  only sessions whose project name contains text
--models <id,id,...>              models to replay on (see --list-models)
--openai-ratio <n>                GPT tokens per Claude token (default: 1, an assumption)
--no-sidechain                    ignore subagent (sidechain) requests
--prices <file>                   your own price table (same shape as prices.json)
--json / --html <file>            machine-readable output / HTML report

You can also pass .jsonl files or directories as arguments, and cost-cliff detects the format of each file.

How it works

1. Parse. For Claude Code, cost-cliff reads assistant lines and their usage. It dedupes on message id, because Claude Code writes one line per content block, and it treats each server-side iteration as its own model call. For Codex, it reads token_count events (last_token_usage), dedupes repeated snapshots, and takes the model from turn_context.
2. Size each request. Prompt size = uncached input + cache writes (5m and 1h) + cache reads. This is the number vendors use to pick a tier.
3. Price it. For each target model, cost-cliff picks the tier from the prompt size and bills the whole request at that tier. It keeps the original cache split and uses each model's own cache-hit multiplier (0.05× on Opus/Sonnet 5.5, 0.1× elsewhere).
4. Convert tokenizers when needed. Claude 4.7 and later produce about 30% more tokens than earlier Claude models (Anthropic's figure), and cost-cliff applies that. Vendors publish no Claude↔GPT ratio, so the default is 1.0 and you can override it with --openai-ratio.

All prices are in prices.json, with source links and a retrieval date. To use your own (for example, negotiated rates), pass --prices my.json.

Limitations

• Same trajectory. A different model would write different output, take a different number of turns and compact at different times. The replay tells you what these requests would cost, not what a whole session on that model would cost.
• Context-window limits are not checked.
• Effort level isn't modeled separately. Thinking tokens are already counted in the logged output.
• List prices only: no batch, Flex, Priority, enterprise discounts or subscription plans. For subscription users, the "actual" number is what the same usage would cost on the API, not what you paid.
• OpenAI lists no cache-write price for gpt-5.5, so those writes are billed at the input rate. GPT-5.6 Sol pricing is promotional.
• The log formats are undocumented and could change. Please open an issue with a redacted line if parsing breaks.

Roadmap

• --what-if-compact <N>: estimate savings from compacting before a tier line.
• Per-session and per-project breakdowns, plus "which sessions would suit Haiku" hints.
• A price-table update command and more vendors (Gemini, DeepSeek).
• Read AUDR records.

License

MIT. Prices belong to their vendors and are reproduced for comparison. Check the linked pages before you make budget decisions.