GPT-5.1 vs GLM-5.1
OpenAI against Z.ai (GLM), costed on the same three workloads. GLM-5.1 is cheaper on all three workloads.
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Monthly bill, side by side
| Workload | GPT-5.1 | GLM-5.1 | Difference |
|---|---|---|---|
| Support chatbot 2,500 six-turn conversations a day |
$6,553 | $4,586 | $1,968 (+43%) |
| Document summarizer 1,000 single-shot summaries a day |
$698 | $618 | $79.50 (+13%) |
| Coding agent 200 twelve-turn sessions a day |
$4,185 | $3,463 | $722 (+21%) |
No prompt caching and no batch discount on either side, so the comparison is like for like. Both figures assume 30 days a month.
The rate cards
| GPT-5.1 | GLM-5.1 | |
|---|---|---|
| Input, per 1M tokens | $1.25 | $1.4 |
| Output, per 1M tokens | $10 | $4.4 |
| Cached input | $0.125 | $0.26 |
| Context window | 272K | 200K |
| Maximum output | 128K | 128K |
| Reasoning model | yes | yes |
| Vision | yes | no |
Beyond the price
- GPT-5.1 reads up to 272K tokens of context in one request; GLM-5.1 stops at 200K.
- Only GPT-5.1 accepts images as input.
- Cached input costs 90% less than fresh input on GPT-5.1 and 81% less on GLM-5.1, which matters most for workloads that resend the same prompt.
Run this comparison on your own numbers
Full detail: GPT-5.1 pricing · GLM-5.1 pricing
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Common questions
Which is cheaper, GPT-5.1 or GLM-5.1?
GLM-5.1 is cheaper on all three workloads.
How much would GPT-5.1 and GLM-5.1 cost each month?
On PromptSpend's standard workloads, per month: support chatbot: GPT-5.1 $6,553, GLM-5.1 $4,586 (GLM-5.1 is cheaper by $1,968); document summarizer: GPT-5.1 $698, GLM-5.1 $618 (GLM-5.1 is cheaper by $79.50); coding agent: GPT-5.1 $4,185, GLM-5.1 $3,463 (GLM-5.1 is cheaper by $722). No prompt caching and no batch discount is assumed.
How do GPT-5.1 and GLM-5.1 differ apart from price?
GPT-5.1 reads up to 272K tokens of context in one request; GLM-5.1 stops at 200K. Only GPT-5.1 accepts images as input. Cached input costs 90% less than fresh input on GPT-5.1 and 81% less on GLM-5.1, which matters most for workloads that resend the same prompt.