GPT-5.1-Codex-Max API Pricing
OpenAI · context window 400K · prices updated 2026-09-15
Where GPT-5.1-Codex-Max sits on price
At $10.00 per million output tokens, GPT-5.1-Codex-Max is a premium tier model — 4.8× the median output price of $2.08, which puts it cheaper than 22% and pricier than 78% of the models we track. It sits 59th cheapest of the 92 OpenAI models we track. Output costs 8.0× more than input here, so anything that makes the model write less — tighter instructions, structured output, lower max_tokens — moves the bill more than trimming the prompt.
Cached input is 90% cheaper. On an input-heavy workload you need roughly a 28% cache-hit rate to take 25% off the input line — reachable for chatbots and agents that resend the same system prompt and history.
What real workloads cost on GPT-5.1-Codex-Max
These three workloads are the ones teams actually run on a premium-priced model — a $10.00/1M model is not bought for the same job as one ten times the price.
| Workload | Per request | Per month |
|---|---|---|
| Support chatbot — 500 conversations/day (5K in / 1.4K out) Conversation history re-sent each turn — the classic prompt-caching win. | $0.0203 | $304 |
| Coding agent — 300 sessions/day (60K in / 12K out) Multi-step loops re-read the same files; caching matters more than raw price. | $0.195 | $1755 |
| Long-context analysis — 200 runs/day (250K in / 4K out) Only possible on large-context models; input cost is nearly the whole bill. | $0.3525 | $2115 |
Model your exact traffic in the API cost calculator — it preloads GPT-5.1-Codex-Max with caching and batch options.
GPT-5.1-Codex-Max price history
GPT-5.1-Codex-Max's price has not moved since we began tracking it on Aug 2, 2026 — 44 days of stability in a market where 78 of the 334 models we track have repriced over the same period, including 9 of OpenAI's own 92 models.
Change-points from our daily price snapshots (tracking since Aug 2, 2026; intraday moves between snapshots are not captured).
GPT-5.1-Codex-Max vs Claude Sonnet 5
The closest-priced alternative from another vendor is Claude Sonnet 5 (Anthropic) — priced within a rounding error on output, with $0.75 more per million input tokens. When two models land this close on price, the decision is quality on your own workload, not the price sheet: run 50 real requests through both and compare.
See Claude Sonnet 5 pricing →Cheaper alternatives
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Frequently asked questions
› How much does the GPT-5.1-Codex-Max API cost?
GPT-5.1-Codex-Max costs $1.25 per million input tokens and $10.00 per million output tokens, with cached input at $0.125 per million (90% cheaper). That works out to roughly 100,000 output tokens per dollar.
› What does the support chatbot workload cost on GPT-5.1-Codex-Max?
Support chatbot — 500 conversations/day (5K in / 1.4K out) costs about $0.0203 per request and $304 per month on GPT-5.1-Codex-Max. Conversation history re-sent each turn — the classic prompt-caching win.
› What does it cost to fill GPT-5.1-Codex-Max's 400K context window?
Sending 400K of input in a single request costs $0.5 at $1.25 per million tokens — before any output. With prompt caching that same fill drops to about $0.05 on repeat requests. This is why large context windows are cheap to advertise and expensive to actually use.
› Is GPT-5.1-Codex-Max worth the price?
GPT-5.1-Codex-Max sits in the middle of the market (59 of 92 by price within OpenAI). The honest test is a routing experiment: send the same 200 real requests to this model and to a tier below, and compare failure rate against the price gap — most teams find a majority of traffic never needed the pricier model.