Token Price Index Methodology
Version 1.2 · Updated September 30, 2026 · Base: March 2023 = 100
1. Universe
The index universe is a curated registry of notable commercial models with dated price histories (src/data/pricingHistory.json), joined to BenchLM's live pricing table for the current month. New models enter the registry at launch; the registry is refreshed from the live table on each monthly release, recording price changes at the date they were observed — never back-dated.
2. Blended price
Each constituent's price is blended as (3 × input + output) / 4 per 1M tokens, assuming a 3:1 input:output token ratio. This matches the blending used across BenchLM's pricing statistics.
3. Activity rules
A constituent is active in month M if it launched on or before M, has not been superseded (an explicit supersession in its history exits it that month), and its price was confirmed within the trailing 12 months. Stale listings are treated as deprecated and drop out.
4. Index formula
Each tier's sub-index for month M is the median blended price of its active constituents, normalized so the tier's first month with data = 100. The headline index is the frontier tier, based at March 2023 = 100 (GPT-4 launch). Medians, not means, so a single extreme price cannot move the index.
5. Tiers
Every constituent carries a published tier: frontier (flagship, top-capability line), mid-tier (workhorse models), or budget (small/cheap models). Assignments are versioned in code and listed below; a model's tier does not change after entry unless the methodology version is bumped.
6. Revisions
The index is fully recomputed from source data on every site build — there are no frozen vintages. Rule or constituent changes revise history and are tracked in git with a methodology version bump. A build-time validator fails the build if the published series drifts from a fresh recomputation.
7. Revision log
v1.2 (September 22, 2026): Claude Opus 5.5 entered the frontier constituent tier at its confirmed launch list price. v1.1 (September 2, 2026): the constituent universe was extended to the 2026 flagship, workhorse, and small lines (GPT-5.5 and 5.6, Claude Opus 4.8 and 5, Claude Fable 5 and 5.1, Claude Sonnet 5, Grok 4.6, Kimi K3, Gemini 3.6 Flash). Each enters at its confirmed release date at the list price recorded in the pricing table; introductory rates are recorded where the provider published them. Provider retirements recorded in the model lifecycle registry now exit constituents on their effective date (Claude 3 Sonnet, Claude 3.5 Sonnet, Claude 3 Haiku), and Gemini 1.5 Pro and Flash are superseded by their 2.5 successors at the successors' registry date, matching the existing GPT-4 and Claude 3 Opus convention. The live-price join keeps the first (standard-rate) row when a model is listed more than once. History was recomputed under these rules. v1.0 (initial release) tracked 34 constituents through mid-2026.
8. Caveats
Early history is thin: March 2023 opens with a single frontier constituent (GPT-4), and sub-indexes begin when their tiers first have data. Prices are list prices for standard API tiers — caching, batch, and volume discounts are out of scope for v1.
Current constituents and tier assignments
Frontier (22)
| Model | Creator | Blended $/1M |
|---|---|---|
| DeepSeek R1 | DeepSeek | $0.96 |
| Grok 4.6 | xAI | $3.00 |
| GPT-5.1 | OpenAI | $3.44 |
| Gemini 2.5 Pro | $3.44 | |
| o3 | OpenAI | $3.50 |
| GPT-4o | OpenAI | $4.38 |
| Gemini 3.1 Pro | $4.50 | |
| GPT-5.2 | OpenAI | $4.81 |
| GPT-5.4 | OpenAI | $5.63 |
| Grok 4.1 | xAI | $6.00 |
| Kimi K3 | Moonshot AI | $6.00 |
| Claude Opus 5.5 | Anthropic | $8.00 |
| GPT-5.6 Sol | OpenAI | $8.00 |
| Claude Opus 4.6 | Anthropic | $10.00 |
| Claude Opus 4.8 | Anthropic | $10.00 |
| Claude Opus 5 | Anthropic | $10.00 |
| GPT-5.5 | OpenAI | $11.25 |
| Claude Fable 5 | Anthropic | $20.00 |
| Claude Fable 5.1 | Anthropic | $20.00 |
| o1 | OpenAI | $26.25 |
| GPT-5.4 Pro | OpenAI | $67.50 |
| GPT-5.5 Pro | OpenAI | $67.50 |
Mid-tier (11)
| Model | Creator | Blended $/1M |
|---|---|---|
| DeepSeek V3 | DeepSeek | $0.48 |
| Mistral Large 3 | Mistral | $0.75 |
| Gemini 3 Flash | $1.13 | |
| Gemini 3.6 Flash | $1.50 | |
| GPT-5.4 mini | OpenAI | $1.69 |
| o3-mini | OpenAI | $1.93 |
| GPT-4.1 | OpenAI | $3.50 |
| Claude Sonnet 5 | Anthropic | $4.00 |
| GPT-5.6 Terra | OpenAI | $4.50 |
| Claude Sonnet 4.5 | Anthropic | $6.00 |
| Claude Sonnet 4.6 | Anthropic | $6.00 |
Budget (8)
| Model | Creator | Blended $/1M |
|---|---|---|
| GPT-4.1 nano | OpenAI | $0.17 |
| GPT-4o mini | OpenAI | $0.26 |
| Grok 3 Mini | xAI | $0.35 |
| GPT-5.6 Luna | OpenAI | $0.45 |
| GPT-5.4 nano | OpenAI | $0.46 |
| GPT-4.1 mini | OpenAI | $0.70 |
| Gemini 2.5 Flash | $0.85 | |
| Claude Haiku 4.5 | Anthropic | $2.00 |
Questions about a rule or a constituent? The computation lives in scripts/lib/compute-price-index.js in the site's repository and is validated on every build. See the index itself at /token-price-index or download the series at /data/price-index.json.