USE CASE · VERIFIED 2 OCT 2026
What's the cheapest AI API for a coding assistant?
For a coding workload of 200M input and 40M output tokens a month, GPT-6 Luna is the cheapest at $40/mo, followed closely by Qwen3.8 Flash ($49/mo) and GLM 5.3 Flash ($50/mo). GPT-4o mini and DeepSeek V4.1 Flash tie at $54/mo, so there are now five budget models under $55/mo for this workload.
Worked example: 200M input, 40M output tokens/month
A coding assistant with moderate codebase context reused across many requests. The six cheapest of the 30 models we track, plus two flagships for scale. Open-weight models are priced at the original provider's own list price.
Why coding workloads favor cheap input pricing
Coding assistants typically send a lot of context — open files, surrounding code, project structure — on every request, but generate relatively short completions in comparison. That means the input price per 1M tokens matters more than the output price for most of these workloads, and it's why models like GPT-6 Luna ($0.1/$0.5) and Qwen3.8 Flash ($0.15/$0.47) come out ahead of models with flashier output but pricier input. If your assistant generates longer responses — full file rewrites, long diffs, verbose explanations — the output price starts to matter more, and something like DeepSeek V3 ($0.27/$0.41) with its unusually low output cost relative to input can look more attractive despite a higher input rate.
Budget, mid, and flagship: what you give up by going cheap
The budget tier (GPT-6 Luna, Qwen3.8 Flash, GLM 5.3 Flash, GPT-4o mini, DeepSeek V4.1 Flash, DeepSeek V3, MiniMax M3, MiMo V2.6 Pro, Gemini 2.5 Flash) covers this workload for $40–$160/mo. Mid-tier models like DeepSeek V4 Pro, Gemini 3 Flash, Claude Sonnet 5/5.5, and GPT-6.1 Sol run $211–$800/mo, and flagship models like Claude Opus 5, GPT-5.5, and GPT-6 Astra run up to $4,000/mo for the identical token volume. Cheaper models aren't automatically worse for coding — several budget options here have 1M context windows, same as many flagships — but this data only tracks price, not output quality, so you still need to test a model against your actual codebase and task mix before committing.
Context window, caching, and batching change the real cost
Context window size matters separately from price: GPT-4o mini and GPT-4o are capped at 128K, while most other models here — including several of the cheapest ones — offer 1M or more, which matters if your assistant needs to hold a large codebase or long conversation history in context. Beyond the headline per-token price, two things can lower your real bill further: prompt caching, which many providers offer for repeated or reused context (common in coding assistants that resend similar codebase context across requests) and often cuts the effective cost of that reused input by around half or more, and batching, which can reduce cost for non-interactive or async requests. Neither is reflected in the numbers above, so your actual monthly cost may be lower than the flat-rate figures shown here if your provider supports caching and you're reusing context heavily.
How we'd actually decide
- Situation: You want the absolute lowest cost and don't need huge context — GPT-6 Luna — cheapest overall at $40/mo with a 1M context window.
- Situation: You want a budget model but prefer an established provider ecosystem — GPT-4o mini — $54/mo, OpenAI's budget tier, though limited to 128K context.
- Situation: Your assistant generates long outputs (full rewrites, long explanations) rather than short diffs — DeepSeek V3 — $0.41 per 1M output is the lowest output price among budget models, giving you $70/mo even with a higher input rate.
- Situation: You need a large context window plus very low cost, no tradeoff — Qwen3.8 Flash or GLM 5.3 Flash — both offer 1M context at $49–$50/mo, nearly matching GPT-6 Luna.
Worked example uses standard (non-batch, non-cached) list pricing verified 2 October 2026. Prices change; use the calculator for today's numbers with your own volume.