Model comparison
Claude Mythos 5.1 vs GLM 5.3
Anthropic against Z.ai, compared on context, price, and verified benchmark results.
Catalog record checked September 3, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below
Anthropic
Claude Mythos 5.1
Frontier
Z.ai
GLM 5.3
Frontier · Open weights
| Specification | Claude Mythos 5.1 | GLM 5.3 |
|---|---|---|
| Provider | Anthropic | Z.ai |
| Tier | Frontier | Frontier |
| Context window | Not verifiedUnverified | 1M |
| Max output | Not verifiedUnverified | 128K |
| Input / 1M tokens | $10 | Winner: $1.40 |
| Output / 1M tokens | $50 | Winner: $4.40 |
| Weights | Closed | Open |
| Parameters | cyber/bio research variant of Fable 5.1 | 753B total (MoE; active count unpublished) |
| Reasoning levels | adaptive | low, high, max |
| Modalities | text, image | text |
| License | Not disclosedUnverified | glm-5.3 (custom) |
| API model id | claude-mythos-5 | glm-5.3 |
| Released | September 1, 2026 | August 14, 2026 |
| Artificial Analysis Intelligence Index [max] (2026-08-14) | Not verifiedUnverified | 60 |
| Terminal-Bench 2.1 (2026-08-14) | Not verifiedUnverified | 88.2 |
| DeepSWE 1.1 (2026-08-14) | Not verifiedUnverified | 66.9 |
| Humanity's Last Exam (2026-08-14) | Not verifiedUnverified | 62.5 |
| SWE-bench Verified (2026-09-01) | Not verifiedUnverified | 95.4 |
Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.
Benchmark receipts
- 2026-09-01: vals.ai SWE-bench Verified leaderboard (independent, mini-swe-agent bash-only); Zhipu docs list 77.8 inherited from GLM-5 — attribution contested, both notedReal GitHub issue resolution: does the model's patch pass the hidden tests. Comparability: comparable with caveat — Post-audit vendor claims and pre-audit scores sit on different task trust levels; scaffolding (agent harness, compute budget) also dominates results. Never aggregate across scaffolds.
- 2026-08-14: Z.ai GLM-5.3 blog + HF model card (vendor, with tools, full set)Agentic terminal work: multi-step tasks executed in a sandboxed shell environment. Comparability: comparable with caveat — Scores across Terminal-Bench major versions (v1 vs v2) are NOT comparable; harness configuration (container, time limits) also shifts results.
- 2026-08-14: Artificial AnalysisComposite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).
Pricing tiers: Claude Mythos 5.1: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview. · GLM 5.3: Token API listed at $1.40/$4.40 per MTok from 2026-08-18 (cached input $0.26); Coding Plan access on a points quota. 1M context, 128K max output per official docs; thinking always on. 753B total MoE per the Hugging Face card (active count unpublished).
Claude Mythos 5.1
Claude Mythos 5.1 is Anthropic's most capable model for cybersecurity and biology research — the Fable 5.1 model with fewer cyber/bio safeguards, restricted to vetted US organisations.
Best for
- Cyber-defence research
- Biology research
- Claude Security workloads
Watch out
Invite-only (vetted US organisations, verification programmes); 30-day data retention applies by default. Same underlying model as Fable 5.1 — most teams should just use Fable.
GLM 5.3
GLM 5.3 is Zhipu's flagship (~753B MoE), near the top of the leaderboards, and the current GLM Coding Plan default.
Best for
- Coding Plan subscribers
- Long-horizon coding
- Chinese + English
Watch out
Open weights dropped 2026-08-28 under Z.ai's custom glm-5.3 licence (not a standard open-source licence — review before commercial use; secondary coverage says >$10B-revenue providers need a security review). 5.2/5.1 Coding Plan requests route to 5.3.
When the cheaper one wins
GLM 5.3 is cheaper on output at $4.40 per million tokens against $50 for Claude Mythos 5.1 — about 11×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.
Run the model pickerEvidence confidence: Medium
How strong and complete the evidence behind this comparison is — not a prediction of which model is better.
- Pricing verified on both sides — Input and output rates are verified for both models.
- 3/5 core specs verified on both sides — Not published for at least one side: context window, max output.
- No shared named benchmark — No benchmark has been measured on both models.
- Verified within the last 90 days — Newest catalog check was 8 days ago.
- Both models carry source citations — Each side has at least two catalog sources on record.
Source receipts
Each catalog figure was checked against the provider or an independent second source on the date shown.
- Claude Mythos 5.1: Anthropic — Claude Mythos (accessed 2026-09-03)
- Claude Mythos 5.1: Anthropic — model deprecations (claude-mythos-5) (accessed 2026-09-03)
- GLM 5.3: Z.ai GLM-5.3 announcement (accessed 2026-08-29)
- GLM 5.3: Hugging Face — zai-org/GLM-5.3 (weights, 2026-08-28) (accessed 2026-08-30)
Related comparisons
- GLM 5.3 vs Grok 4.5
- Claude Fable 5.1 vs Claude Mythos 5.1
- Claude Fable 5.1 vs GLM 5.3
- Claude Fable 5 vs Claude Mythos 5.1
- Claude Fable 5 vs GLM 5.3
- Claude Haiku 4.5 vs Claude Mythos 5.1
Diving deeper on one model? Claude Mythos 5.1 · GLM 5.3
Common questions
Claude Mythos 5.1 vs GLM 5.3
Answered from the verified figures on this page rather than general guidance.
Is Claude Mythos 5.1 or GLM 5.3 cheaper for input?
GLM 5.3 is cheaper at $1.40 per million input tokens, against $10 for Claude Mythos 5.1 — roughly 7.1× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Mythos 5.1 has tiered pricing: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview. GLM 5.3 has tiered pricing: Token API listed at $1.40/$4.40 per MTok from 2026-08-18 (cached input $0.26); Coding Plan access on a points quota. 1M context, 128K max output per official docs; thinking always on. 753B total MoE per the Hugging Face card (active count unpublished).
Is Claude Mythos 5.1 or GLM 5.3 cheaper for output?
GLM 5.3 is cheaper at $4.40 per million output tokens, against $50 for Claude Mythos 5.1 — roughly 11× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Mythos 5.1 has tiered pricing: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview. GLM 5.3 has tiered pricing: Token API listed at $1.40/$4.40 per MTok from 2026-08-18 (cached input $0.26); Coding Plan access on a points quota. 1M context, 128K max output per official docs; thinking always on. 753B total MoE per the Hugging Face card (active count unpublished).
Do Claude Mythos 5.1 and GLM 5.3 support the same reasoning levels?
Claude Mythos 5.1 exposes adaptive, while GLM 5.3 exposes low, high, max.
Should I use Claude Mythos 5.1 or GLM 5.3?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Claude Mythos 5.1 suits cyber-defence research; GLM 5.3 suits coding plan subscribers.
Can I self-host Claude Mythos 5.1 or GLM 5.3?
GLM 5.3 publishes open weights, but self-hosting and third-party provider access depend on the licence, hardware, serving support, and availability. Claude Mythos 5.1 is a closed model whose supported access paths are controlled by its provider.
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Input price: GLM 5.3 costs $1.40 per 1M tokens versus $10 for Claude Mythos 5.1 — a 7.1x difference at the headline tier.
- Deployment: GLM 5.3 publishes weights you can self-host; the other is API-only.
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.