GLM-5.1 vs GPT-5.5 Instant
GLM-5.1 (2026) and GPT-5.5 Instant (2026) are frontier reasoning models from Zhipu AI and OpenAI. GLM-5.1 ships a 200k-token context window, while GPT-5.5 Instant ships a 400k-token context window. On pricing, GLM-5.1 costs $1.05/1M input tokens versus $5/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing.
GLM-5.1 is ~376% cheaper at $1.05/1M; pay for GPT-5.5 Instant only for coding workflow support.
Decision scorecard
Local evidence first| Signal | GLM-5.1 | GPT-5.5 Instant |
|---|---|---|
| Best for | reasoning-heavy apps, tool-calling agents, and provider-routed production | multimodal apps and tool-calling agents |
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 200k | 400k |
| Cheapest output | $3.50/1M tokens | $30/1M tokens |
| Provider routes | 5 tracked | 1 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- GLM-5.1 has the lower cheapest tracked output price at $3.50/1M tokens.
- GLM-5.1 has broader tracked provider coverage for fallback and procurement flexibility.
- GLM-5.1 uniquely exposes Reasoning in local model data.
- Local decision data tags GLM-5.1 for Coding, RAG, and Agents.
- GPT-5.5 Instant has the larger context window for long prompts, retrieval packs, or transcript analysis.
- GPT-5.5 Instant uniquely exposes Vision and Multimodal in local model data.
- Local decision data tags GPT-5.5 Instant for Coding, RAG, and Agents.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
GLM-5.1
$1,715
Cheapest tracked route/tier: OpenRouter
GPT-5.5 Instant
$11,500
Cheapest tracked route/tier: OpenAI API
Estimated monthly gap: $9,785. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for GLM-5.1 and GPT-5.5 Instant; plan for SDK, billing, or endpoint changes.
- GPT-5.5 Instant is $26.50/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Reasoning before moving production traffic.
- GPT-5.5 Instant adds Vision and Multimodal in local capability data.
- No overlapping tracked provider route is sourced for GPT-5.5 Instant and GLM-5.1; plan for SDK, billing, or endpoint changes.
- GLM-5.1 is $26.50/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Vision and Multimodal before moving production traffic.
- GLM-5.1 adds Reasoning in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-04-07 | 2026-05-05 |
| Context window | 200k | 400k |
| Parameters | 754B total, 40B active | — |
| Architecture | mixture of experts | decoder only |
| License | MIT | Proprietary |
| Knowledge cutoff | 2025-11 | 2025-08 |
Pricing and availability
| Pricing attribute | GLM-5.1 | GPT-5.5 Instant |
|---|---|---|
| Input price | $1.05/1M tokens | $5/1M tokens |
| Output price | $3.50/1M tokens | $30/1M tokens |
| Providers |
Capabilities
| Capability | GLM-5.1 | GPT-5.5 Instant |
|---|---|---|
| Vision | No | Yes |
| Multimodal | No | Yes |
| Reasoning | Yes | No |
| Function calling | Yes | Yes |
| Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | Yes | Yes |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on vision: GPT-5.5 Instant, multimodal input: GPT-5.5 Instant, and reasoning mode: GLM-5.1. Both models share function calling, tool use, structured outputs, and code execution, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
For cost, GLM-5.1 lists $1.05/1M input and $3.50/1M output tokens on the cheapest tracked provider, while GPT-5.5 Instant lists $5/1M input and $30/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts GLM-5.1 lower by about $10.71 per million blended tokens. Availability is 5 providers versus 1, so concentration risk also matters.
Choose GLM-5.1 when coding workflow support, lower input-token cost, and broader provider choice are central to the workload. Choose GPT-5.5 Instant when coding workflow support and larger context windows are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions. It also helps separate model capability from provider packaging, which can change cost and latency.
FAQ
Which has a larger context window, GLM-5.1 or GPT-5.5 Instant?
GPT-5.5 Instant supports 400k tokens, while GLM-5.1 supports 200k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is cheaper, GLM-5.1 or GPT-5.5 Instant?
GLM-5.1 is cheaper on tracked token pricing. GLM-5.1 costs $1.05/1M input and $3.50/1M output tokens. GPT-5.5 Instant costs $5/1M input and $30/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is GLM-5.1 or GPT-5.5 Instant open source?
GLM-5.1 is listed under MIT. GPT-5.5 Instant is listed under Proprietary. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for vision, GLM-5.1 or GPT-5.5 Instant?
GPT-5.5 Instant has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, GLM-5.1 or GPT-5.5 Instant?
GPT-5.5 Instant has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run GLM-5.1 and GPT-5.5 Instant?
GLM-5.1 is available on Z.ai, OpenRouter, Fireworks AI, Vercel AI Gateway, and Novita AI. GPT-5.5 Instant is available on OpenAI API. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-25. Data sourced from public model cards and provider documentation.