GLM-5.3-Flash vs GPT-6 Astra vs Claude Opus 5.5
GLM-5.3-Flash comes out ahead, 80 to 70 and 68 on our weighted score, and it is the cheaper option too.
- Our pick
Z.ai (Zhipu)GLM-5.3-Flash
80/100- ECI151.9
- Price$0.15 / $0.50
- Context1M
OpenAIGPT-6 Astra
68/100- ECI166.5
- Price$10.00 / $50.00
- Context1.05M
AnthropicClaude Opus 5.5
70/100- ECI167.4
- Price$4.00 / $20.00
- Context1M
GLM-5.3-Flash is our pick
GLM-5.3-Flash is the better all-round choice, scoring 80/100 against Claude Opus 5.5 (70) and GPT-6 Astra (68). It leads on price and inputs & features. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityClaude Opus 5.5Capabilities Index (ECI): Claude Opus 5.5 167.4 · GPT-6 Astra 166.5 · GLM-5.3-Flash 151.9
- Lowest priceGLM-5.3-FlashGLM-5.3-Flash $0.237 · Claude Opus 5.5 $8.00 · GPT-6 Astra $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6 AstraGPT-6 Astra 1,050,000 · GLM-5.3-Flash 1,000,000 · Claude Opus 5.5 1,000,000 tokens
- Widest inputsGLM-5.3-FlashGLM-5.3-Flash: Text, Images, PDFs, Video · GPT-6 Astra: Text, Images, PDFs · Claude Opus 5.5: Text, Images, PDFs
- Self-hostingGLM-5.3-FlashPublishes downloadable weights
| Measure | Weight | GLM-5.3-Flash | GPT-6 Astra | Claude Opus 5.5 |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 81 | 99 | 100 |
| Price | 25% | 79 | 0 | 7 |
| Inputs & features | 15% | 90 | 80 | 80 |
| Context window | 10% | 60 | 61 | 60 |
| Overall | 100% | 80/100 | 68/100 | 70/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | GLM-5.3-FlashZ.ai (Zhipu) | GPT-6 AstraOpenAI | Claude Opus 5.5Anthropic |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 151.9 | 166.5 | 167.4 (best) |
| ECI rank | #42 of 148 | #2 of 148 | #1 of 148 (best) |
| GPQA DiamondGraduate-level science questions | 90.2% | 95.8% (best) | 90.6% |
| FrontierMath Tiers 1–3Research-level mathematics | 55.8% | 93.7% (best) | 91.2% |
| OTIS Mock AIME 2024–2025Competition mathematics | 93.9% | 100% (best) | 100% (best) |
| SimpleQA VerifiedShort factual questions | — | 75.6% (best) | 72.2% |
| Price per million tokens | |||
| Input | $0.15 (best) | $10.00 | $4.00 |
| Output | $0.50 (best) | $50.00 | $20.00 |
| Cached input | $0.03 (best) | $1.00 | $0.20 |
| Blended (3:1) | $0.237 (best) | $20.00 | $8.00 |
| Long-context rate | Same rate | Over 272K: $20.00 / $75.00 | Same rate |
| Price source | Official Z.AI API | Official OpenAI API | Official Anthropic API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,050,000 tokens (best) | 1,000,000 tokens |
| Max output | 131,072 tokens (best) | 128,000 tokens | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | Yes |
| Audio | No | No | No |
| Video | Yes | No | No |
| Reasoning | Yeslow · high · max | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Open | Proprietary | Proprietary |
| API model ID | glm-5.3-flash | gpt-6-astra | claude-opus-5-5 |
| API providers | 65 (best) | 26 | 28 |
| Released | Aug 26, 2026 | Sep 4, 2026 | Sep 22, 2026 |
| Knowledge cutoff | — | Apr 30, 2026 | Jun 2026 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- GLM-5.3-Flash$2.50
- GPT-6 Astra$200.00
- Claude Opus 5.5$80.00
Which should you choose?
Which is better: GLM-5.3-Flash, GPT-6 Astra or Claude Opus 5.5?
GLM-5.3-Flash is the better all-round choice, scoring 80/100 against Claude Opus 5.5 (70) and GPT-6 Astra (68). It leads on price and inputs & features. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, GLM-5.3-Flash, GPT-6 Astra or Claude Opus 5.5?
GLM-5.3-Flash is cheaper at $0.15 input / $0.50 output per million tokens (official Z.AI API price). Claude Opus 5.5 costs $4.00 input / $20.00 output per million tokens (official Anthropic API price); GPT-6 Astra costs $10.00 input / $50.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $0.237 per million tokens for GLM-5.3-Flash versus $8.00 for Claude Opus 5.5 (34× as much) and $20.00 for GPT-6 Astra (84× as much).
Which scores higher on benchmarks?
Claude Opus 5.5 scores higher on the Capabilities Index (ECI): Claude Opus 5.5 167.4 (#1 of 148), GPT-6 Astra 166.5 (#2 of 148) and GLM-5.3-Flash 151.9 (#42 of 148). The confidence ranges of the top two overlap (164.0–172.0 vs 163.1–171.1), so treat the gap as small. On individual benchmarks: GPQA Diamond — GPT-6 Astra 95.8%, Claude Opus 5.5 90.6%, GLM-5.3-Flash 90.2%; FrontierMath Tiers 1–3 — GPT-6 Astra 93.7%, Claude Opus 5.5 91.2%, GLM-5.3-Flash 55.8%; OTIS Mock AIME 2024–2025 — GPT-6 Astra 100%, Claude Opus 5.5 100%, GLM-5.3-Flash 93.9%.
Which is better for coding?
There are no published SWE-bench Verified results for GLM-5.3-Flash, GPT-6 Astra and Claude Opus 5.5 yet, so there is no like-for-like coding score. On overall capability, Claude Opus 5.5 leads, which tends to carry over to coding, but test on your own codebase. All three support tool calling for agent workflows.
Which has the bigger context window?
GPT-6 Astra has the largest context window at 1,050,000 tokens, against 1,000,000 for GLM-5.3-Flash and 1,000,000 for Claude Opus 5.5. Maximum output per response: GLM-5.3-Flash up to 131,072, GPT-6 Astra up to 128,000, Claude Opus 5.5 up to 128,000 tokens.
Which can read images, PDFs, audio or video?
GLM-5.3-Flash accepts text, images, PDFs and video; GPT-6 Astra accepts text, images and PDFs; Claude Opus 5.5 accepts text, images and PDFs. GLM-5.3-Flash handles the widest range of inputs.
Are any of these open source?
GLM-5.3-Flash publishes its weights and can be self-hosted; GPT-6 Astra and Claude Opus 5.5 is proprietary.
Which is newer?
Claude Opus 5.5 is the newest, released Sep 22, 2026. GPT-6 Astra came out Sep 4, 2026; GLM-5.3-Flash came out Aug 26, 2026. Knowledge cutoff: GPT-6 Astra Apr 30, 2026, Claude Opus 5.5 Jun 2026.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
