Chat & text model pricing
Every chat model charges a flat credit amount per assistant message — from 0.5 credits on lightweight models up to 12 on flagship models.
Last updated Sep 6, 2026
Chat and Tutor conversations bill chat credits. The cost depends on which
model answers your message — not on how many tokens you typed, though longer
conversations carry more history into each request.
Credit range (0.5 – 12)
All text models are priced on a compressed 0.5–12 scale:
| Tier | Credits per message | Example models |
|---|---|---|
| Budget | 0.5 | GPT-5 Nano, Gemini 2.5 Flash Lite, DeepSeek V3/V3.1/V3.2/V4 Flash, Qwen3 32B, Qwen3.5 Flash, Tencent Hy3, Mistral Nemo, Llama 4 Scout/Maverick |
| Low | 1.5 | GPT-5 Mini, Gemini 2.5 Flash, Gemini 3 Flash, DeepSeek R1/V4 Pro/Flash, Mistral Medium 3.1 |
| Mid-low | 2 – 2.5 | Claude 3.5 Haiku (2), Qwen3 Max (2), Zack (auto) 2.5, Grok 4.3, GPT-5.6 Luna, GLM 5.2 |
| Mid | 3 – 3.5 | GPT-5, GPT-5.1, Gemini 2.5 Pro, Gemini 3.5 Flash |
| Mid-high | 4.5 – 5.5 | Grok 4.5, Claude Sonnet 5, GPT-5.2, GPT-5.3 Chat, Gemini 3.1 Pro |
| High | 7 – 9 | GPT-5.4, GPT-5.6 Terra, Kimi K3, Claude Sonnet 4 / 4.5 / 4.6 |
| Flagship | 12 | GPT-5.5, GPT-5.6 Sol, Claude Opus 4.8, Fugu Ultra |
Reasoning depth — many models offer a reasoning-level picker (None → Max). Higher
depth can improve hard problems but does not change the per-message credit — you
always pay the flat model rate in the picker. Legacy separate "Medium" model rows
(e.g. GPT-5.2 Medium) were folded into one model + a reasoning picker.
Zack (auto-router) is priced at 2.5 credits per message.
Retired models
Older keys (GPT-4.x, o3, o4-mini, Grok 4) are no longer in the
picker. Old conversations may resolve to successors such as GPT-5.6 Terra or
Grok 4.3 — switch to a current model when prompted.
Default vs named models
| Choice | Best for | Typical cost |
|---|---|---|
| Zack | Everyday use — auto model selection + tools | 2.5 credits |
| Named model | A specific provider / capability | Flat rate shown in the picker |
| + Reasoning | Harder problems on supported models | Same flat rate (no extra credit) |
There are no separate Chat-Thinking / Chat-Fast / Chat-Chinese modes —
use Zack, a named Chinese-capable model (e.g. DeepSeek / Qwen), or raise
Reasoning when you need deeper thinking.
Agent tools (also chat credits)
Agent tools run during a chat message and add to the message's chat credit
total. They are tracked separately in transaction history but draw from the same
chat pool.
| Tool | Credits | Notes |
|---|---|---|
| Web search | 10 per search | Charged per search call |
| Website crawl | 2 per URL | Charged per crawled page |
| YouTube transcript | 2.5 per video | Per transcript fetch |
| Image generation (in chat) | 10 per image | Uses chat credits, not Image Studio pool |
| Image edit (in chat) | 10 per image | Same as in-chat generation |
Other agent tools (flashcards, notes, mind maps, slides, etc.) follow the
underlying model's per-message rate for the generation step.
How the per-message cost is calculated (technical)
For each model, Zense AI:
- Reads OpenRouter price per million input/output tokens.
- Applies the representative profile (12k in / 1k out per message).
- Targets ~25% margin against the Pro-plan credit value (0.0495 HKD/credit).
- Compresses the raw cost onto the 0.5–12 table so everyday models stay
affordable and flagships are subsidized by cheaper tiers.
You are billed the final compressed credit, not the raw token math.
Tokens you will see in the UI
Even though billing is per message, each turn records token usage for debugging
and analytics:
- promptTokens — system prompt + history + attachments + tool context sent to
the model. - completionTokens — the assistant's reply.
- reasoningTokens — extra tokens on reasoning models (GPT-5.6, thinking modes, etc.).
A long thread increases promptTokens on later messages, which is why the
pricing formula assumes a heavy input profile — but your credit charge stays the
flat model rate unless you also invoke paid agent tools.
Tips to manage chat spend
- Use Zack or 0.5-credit models for simple questions.
- Reserve flagship models (9–12 credits) for work that needs top quality.
- Web search (10 credits) adds up quickly — ask Chat to search only when needed.
- School admins: set per-user chat caps and monitor the shared pool in School
Management → Users.
Full model-by-model table lives in the engineering docs (
chat-pricing.md). Rates
may be retuned when OpenRouter prices change — check the model picker for live costs.
